days of horse-drawn streetcars. There are no river barriers between it and downtown. Although elevated freeways came later, much of the local street grid maintains continuity beneath the freeway alignments. Hence there is ready accessibility to downtown and nearby neighborhoods without reliance on freeway interchanges.
The contrast with the Upper Westside Project area is stark. Upper Westside is a largely undeveloped agricultural area with a small number of riverfront residences along Garden Highway and a few farmsteads. Upper Westside is separated from downtown by the American and Sacramento rivers with just a few congested crossings. It is also separated from areas to the west by the Sacramento River barrier. To the east, only Garden Highway, West El Camino Avenue, San Juan Drive, Arena Boulevard and Del Paso Road are continuous across the alignments of I-5, I-80 or both. All but San Juan Drive have congested interchanges with one of the freeways, but San Juan drive is only one lane in each direction. This freeway and congestion barrier exists over a distance of 4.5 miles from Garden Highway to the point where I-5 and Routes 70- 99 diverge. In reality, Oak Park neighborhood is well connected to the surrounding community and downtown whereas Upper Westside is highly isolated. This portion of Master Response TR-1 is false and misleading.
In response to comments to the effect that presumed transit service will not be in place until full build-out provides the requisite ridership, Master Response TR-1a states “Transit service is expected to continue to expand as project buildout occurs. As more residences, office space, schools, and retail are added, transit ridership will grow, furthering the need for increased transit service coverage and bus frequencies.” To be accurate, however, the response should acknowledge and disclose t that initial transit services to the early stages of development will be limited in terms of frequency and destinations served.
Master Responses TR-1d and TR-1e concern the adequacy of transit mitigation and the funding of it. Although the Master Response asserts the transit mitigation services provided and the funding of it will be adequate, two problems are evident.
• The financing plan assumes that the Project will contribute approximately $12.8 million to the transit component of the Sacramento County Transportation Development Fee fund. While this superficially seems a significant amount of capital, when one realizes that a typical 40-foot zero emissions transit coach costs between $1.4 and $1.6 million (that is, the $12.8 million could buy just 8 or 9 buses),the concern for adequacy of funding remains very real.
• The financing plan also assumes that the project area will be annexed to a County Service Area or form a transportation services district through which the ultimate occupants of the project can vote to tax themselves to Mr. Patrick Soluri
Soluri Meserve
August 19, 2025
provide transit service operations. Since success of any such vote by currently unknown future occupants is speculative, transit mitigations are not presently enforceable and so the transit impact must be classified as Significant and Unavoidable.
Master Response TR-2: Garden Highway Safety
Master Response 2 is a safety analysis of Garden Highway. Two issues stand out. One is that the response does not consider the increased difficulty of safely accessing and egressing the driveways of the riverfront homes that line the west side of Garden Highway under increased traffic pressure along that roadway.
The second is that the response notes that the Street 9 connection to Garden Highway is being contemplated for removal by the project applicant. The FEIR must make clear whether the Street 9 connection is or is not being removed, otherwise the project description is shifting and unstable.
Master Response TR-3: Traffic Congestion
This master response summarizes the findings of the Local Transportation Analysis that was carried out for the Project, Identified as Appendix TR-2 in the DEIR. As noted in the master response, although congestion-based assessments are no longer a CEQA matter, it is still relevant to the development review process. It identifies deficiencies that are inconsistent with General Plan operational standards and the improvements needed to provide conformance.
While the deficiencies and effectiveness of the necessary improvements, if feasible, are not relevant to the adequacy of the CEQA document, they are highly relevant to General Plan consistency and thus whether the governing body may approve the Project.
As the master response points out, by the EIR preparers own estimates, the Project would generate over 100,000 daily trips external to the Project site. The Local Transportation Analysis (“LTA”) identifies numerous locations where improvements would be needed at numerous locations under jurisdiction of the County, the City of Sacramento or Caltrans. Although the LTA suggests possible improvements, in most cases, because of conflicts in policies and goals, right-of- way limitations, unconventional designs and compounding circumstances, the necessary improvements are infeasible.
What Master Response TR-3 fails to state is that approval of the Project would leave massive congestion on County, City and Caltrans facilities unmitigated.
Mr. Patrick Soluri
Soluri Meserve
August 19, 2025
Comment and Response 19-105
Our comment states that in light of the extensive and significant operational and safety deficiencies related to excessive freeway off and on ramp queues at several interchanges in the Project vicinity that the DEIR discloses, the Project should not be approved until there is clear agreement among the agencies having jurisdiction as to what the actual mitigation plans are, how full funding would be accomplished and when construction will take place.
The response attempts to evade the issues in the comment, stating that it is unrealistic to expect all applicable agencies to agree in advance of the project’s approval to the precise mitigation, cost, and how full funding will be achieved.
Caltrans typically does not become involved in these types of discussions until a proposed improvement is formally initiated through the Caltrans project development process.
While what the response states is typically true of Caltrans, in this case both Caltrans and the City of Sacramento have commented extensively concerning the operational and safety issues the Project causes that necessitate transportation improvements. For example, in the case of the I-80 / West El Camino interchange, Caltrans in comment 4-16 expresses skepticism regarding the unconventional Class 1 path through the interchange on the north side of West El Camino as part of the interchange reconstruction and the City, as part of Comment 12-24, notes that because the interchange is outside the County of Sacramento, thus precluding the County from serving as lead agency, and Sacramento County cannot compel the City and Caltrans to approve and allow construction of the specified improvements. The City also notes the same is true for the ramps at the interchange of I-5 with Garden Highway.
Comment and Response 19-106
This comment inquired what mitigation was proposed for the I-5 southbound off ramp at J Street which experiences excessive queuing. The FEIR responds by reference to its response to Caltrans comment 4-5. That response introduces a new analysis of the situation, which blames the queuing on backspill from a ramp farther south and also claims the queues on the J Street ramp have been reduced by the prevalence of working remotely caused by the pandemic. But the FEIR admits this condition occurred following the Project’s baseline conditions, which the FEIR concedes are pre-pandemic conditions. Thus, post-pandemic conditions are irrelevant here. And while lead agencies are sometimes allowed to base their CEQA analysis on future conditions, the EIR asserts that project build out will occur over several decades. The temporary pandemic conditions that existed in in 2021 and 2022 have already started to be reversed as more and more workers are required to report to their normal job stations.
Mr. Patrick Soluri
Soluri Meserve
August 19, 2025
Comment and Response 19-107
This comment concerned mitigation of excessive queuing at the I-5 interchanges with Arena Boulevard, and with Del Paso Road Garden Highway, the DEIR concludes that the excessive off ramp queuing is caused by backups from adjacent cross-street intersections that impair movements from the exit ramps.
The DEIR proposes at DEIR page 22-68 to pay fair share funds toward improvements to the intersections of Arena with El Centro and Arena with East Commerce Way which, according to the analysis, would allow the off ramps to operate without hazardous queue spill-backs onto the I-5 mainline.
The text on DEIR page 22-68 continues as follows:
“With respect to the off-ramp queues at the two remaining study interchanges (I-5/Arena Boulevard1 and I-5/Garden Highway) a variety of potential surface street improvements were tested along the roadways leading to this [sic] facility. This involved collaboration with staff from the City of Sacramento regarding the viability of certain improvements.
Improvements such as lane restriping, adding lanes or modifying signal phasing were either found to not to be effective or could also cause the need for additional right-of –way. At both interchanges the following conclusions were reached. First, there are no known improvements planned at either interchange. Second, the feasibility of any surface street improvements that could reduce off-ramp queuing is not known.”
Now, FEIR response states “In summary, the recommended mitigation measures are more targeted, more cost efficient, and would more effectively address the queuing issues than adding more off-ramp vehicle storage, since the queuing on the off-ramp is not due to the capacity of the off-ramp but due to the capacity of adjacent surface street intersections.
The FEIR fails to explain what changed. How did the feasibility of any surface street improvements that could reduce off-ramp queuing go from being not known to being more targeted, more cost efficient and more effectively address the queuing issues? No new analysis is indicated.
We also note the City of Sacramento’s Comment 12-24 includes the following statements. “The DEIR continues to rely on fair share contributions toward roadway widening projects within City limits without adequately addressing our concerns about implementation responsibility. ..The DEIR does not propose alternative mitigation approaches that avoid placing implementation responsibility on the City, nor does it explain how these projects would be fully funded and executed given the City's financial constraints.” The EIR therefore fails to provide
1 We think the authors meant to say I-5/Del Paso Road here.
Mr. Patrick Soluri
Soluri Meserve
August 19, 2025
adequate information demonstrating that proposed “fair share” funding will be effective.
Comment and Response 19-108
This comment concerned excessive on-ramp queues at the I-5 southbound loop on ramp from Garden Highway2 and the diagonal on ramp to southbound I-5 from Del Paso Road. The Response clarifies details and elements of confusion.
However, we note the City of Sacramento’s previously cited comments regarding reluctance to commit to paying fair share costs or commit to being lead agency for the improvements remain applicable.
Comments and Responses 19-109 and 19-110
This comment concerned queues on the southbound I-5 off ramp to Del Paso extending north past the merge point between I-5 and Routes 70/99. The Response points out that cumulative deficiencies exist both with and without the Project and Project traffic is not projected to add to these queues. Although this is not a condition the Project may be responsible for mitigating, it constitutes one of the conditions that contributes to diversions described in Comment 19-112
Comment and Response 19-111
This comment concerned issues along Garden Highway. The response is by reference to Master Response TR-2 which has been previously discussed in this letter.
Comment and Response 19-112
This comment expresses concern that, given the congestion forecast along I-5 and at surface street locations, significant numbers of knowledgeable travelers would choose to divert to a calming drive in the pleasant, scenic surroundings of Garden Highway, even though a tense drive on the congested routes might remain faster. This product of human preference could result in considerably more impactful traffic on Garden Highway than predicted in transportation models that tend to assign traffic to the fastest routes.
The response claims that the comment offers no basis for the forecast worsening congestion on I-5. However, the DEIR itself provides extensive evidence of queuing and lane blocking on I-5. For instance, see Comment and response 19- 109 and 19-110. While it is true that most trucks and long distance travelers will stick to the freeways, in the modern era many drivers rely on GPS-based
2 Queues on the diagonal ramp from Garden Highway to I-5 northbound also exceed capacity in the existing and cumulative conditions but the Project is not projected to add any traffic to this movement.
Mr. Patrick Soluri
Soluri Meserve
August 19, 2025
cellphone software to obtain real-time routings that avoid heavy congestion and delay. The response is simply a denial of present reality.
Comment and Response 19-113
This comment expressed concern that by understating the Project’s external trip generation. it avoids disclosing the full extent of the severity of the Project’s VMT and congestion impacts. The response avoids directly responding to the three paragraphs of comment it labels Comment 19-113 by mischaracterizing it a general comment and moving onto respond to sections it labels 19-114 through 19-117. In so doing, the FEIR evades directly responding in good faith to the issue that the DEIR presents no statistical evidence that the project offers a greater mix of land uses, greater overall density, greater walkability, bikeability and transit accessibility that would make it likely to have more internal and fewer external motor vehicle trips than recently developed, comparably sized developed areas to the north and east of the Project site. Consequently there is no justification for the DEIR’s transportation analysts adjusting initial trip generation estimates for the Project based on data from the Institute of Transportation Engineers formerly authoritative publication Trip Generation Manual, 10th Edition,3 by applying a procedure called MXD+ that is purported to account for the special qualities of travel in mixed use developments.
Comment and Response 19-114
This comment observed that the current version of MXD+ was recalibrated to 2019 data from 12 mixed use sites and that the size of the Upper Westside Specific Plan dwarfs the sites used in the calibration in terms of acreage, dwelling units, retail and office space. The Technical Appendix to DEIR Appendix T-1 also describes validation of the MXD+ process to 4 additional mixed use developments. The validation sites ranged in size from 4 acres to 3,000 acres with 3 of the 4 sites being less than 80 acres. Although the 3,000 acre site contains 7704 dwelling units, most are single family and the quantities of other uses (office, retail, grocery, restaurants) are very small.
Response 19-114 presents clouds of information about the development and validation of the original MXD. But the nearly two pages of information about the original MXD do not rebut the fact that the 16 sites used in the 2019 MXD+ recalibration and revalidation are, with just one exception (and in that one case solely based on acreage) are all much, much smaller developments than Upper Westside. There is every reason to believe that the MXD+ process is biased toward the travel characteristics of much smaller mixed use projects with
3 We say ‘formerly authoritative’ because in September, 2021 the Institute released Trip Generation Manual, 11th Edition that supersedes the 10th Edition.
Mr. Patrick Soluri
Soluri Meserve
August 19, 2025
predominantly multi-family housing as opposed to the scale and balance of housing types in the subject UWSP Project.
Comment and Response 19-115
This comment drew attention to the DEIR finding at page 18-30, Table TR-2, that when the UWSP project data is processed through the SACOG SACSIM19 regional transportation model, the results indicate that 15.4 percent of the Projects residential trips would be internal to the Project. If processed through the MXD+ process, the result is 22.9 percent internal trips. This difference suggests the DEIR’s transportation analyst’s choice to of the more favorable to the Project MXD+ results rather than those of the SACSIM tour-based mode is not consistent with CEQA’s requirement of a good faith effort to disclose impact.
This choice causes a critical understatement of the Project’s VMT per capita analysis. If the more conservative and likely more reliable SACSIM19 output is relied upon, the resultant VMT per capita for the Project would be 15.41 miles per capita instead of 14.34. Since 15.41 is above the significance threshold of 14.83 miles per capita, the Project would be found to have significant VMT impact and require mitigation.
Response 19-115 asserts that the difference in VMT is misleading because MDX+ considers all trips including those that are non-home-based, school trips etc., which are often internal to a project area, while implying that SACSIM does not. This is a false implication. SACSIM tours consider seven categories of activities that could be non-home-based trips and does consider school trips.
SACSIM19 also includes a commercial vehicle trip module. The response is inadequate and misleading.
Comment and Response 19-116
This comment concerned possible double counting of trip deductions for internal trips and attracted passerby trips. The point is that since there is virtually no existing traffic on most of the Project streets, any attracted passers-by would have to be internally generated trips. Since the analysis already deducts internal trips, taking a further deduction for attracted passers-by is a double counting of the same people.
The response explains that in its process, internal trips are deducted from the allowable numbers of attracted passers-by suggested by the Institution of Transportation Engineers’ publication Trip Generation Handbook. This is a credible adjustment. However, the analysts should determine whether there is sufficient non-internally generated traffic passing by to sustain the remainder of the assumed passerby deduction.
Mr. Patrick Soluri
Soluri Meserve
August 19, 2025
Comments and Responses 19-117 and 19-118
These comments concern the use of Trip Generation Manual, 10th Edition rather than the 11th Edition which became available in September, 2021. The response notes that the technical work was well under way already in June 2021,in plenty of time for the DEIR analysts to have relied on it for the UWSP work. Since the technical analysis process is highly computerized, we doubt if the task of making changes in the trip generation rates would have been quite as onerous as the response makes it seem. However, we do appreciate the calculated comparisons of the differences in net trip generation which the response provides.
Conclusion
Given the concerns above, and the serious comments made by Caltrans and the City of Sacramento, we believe the County should pause the EIR and reject the Project.
Sincerely,
Smith Engineering & Management
A California Corporation
Daniel T. Smith Jr., P.E.
President
EXHIBIT 3
August 19, 2025
Patrick Soluri
Soluri Meserve, A Law Corporation
510 8th Street
Sacramento, CA 95814
RE: Comments on Upper Westside Project and its Final Environmental Impact Report and Response to Comment 19-54
Mr. Soluri,
The assertion that airborne concentrations of ultrafine particles (UFP) may be inferred from measurements of fine particles (PM2.5) is incorrect. For example, the published research article “Land use regression model for ultrafine particles, fine particles, and black carbon in Southern California” (Science of the Total Environment, Volume 699, 10 January 2020), reports on a measurement campaign for these pollutants in the Los Angeles metropolitan area, at 215 sites across three seasons. It concludes, “UFP and PM2.5 measurements (r=0.001) and predictions (r=0.05) were uncorrelated at the sites.” This article also states, “UFP may be more toxic [than PM2.5] due to unique physiochemical properties that increase their potential for adsorption and interaction with tissues and cellular targets (Health Effects Institute, 2013). Importantly, … they are not well represented by measurements of other PM size fractions including PM10 and PM
2.5.” It also states “the major UFP exposure source is traffic, especially emissions from heavy-duty diesel trucks”, and found that “UFP concentrations were highest at the downwind sites closest to the roadway (50-150 m)”. The authors include respected University of Southern California Professor Constantinos Sioutas, whose research I managed when I was an Air Pollution Research Specialist at the California Air Resources Board’s Air Quality and Science Research Section, focusing on near-road air pollution and its health effects.
Furthermore, several recent research studies show that the health risk from UFP exposure exceeds that from fine particle exposure. For example, • “Unlike PM2.5, UFPs may have much more impacts on human health” (‘Beyond PM2.5: The role of ultrafine particles on adverse health effects of air pollution’, Biochimica et Bioophysica Acta, December 2016) • “Harmful systemic health effects of PM10 or PM2.5 are often attributable to the UFP fraction.” (‘Ultrafine particles: unique physicochemical properties relevant to health and disease’, Experimental & Molecular Medicine, Vol. 52, 2020)
• “For respiratory mortality, we found … that the smallest UFP fractions showed the largest effects.” (‘Impact of Ambient Ultrafine Particles on Soluri Meserve, A Law Corporation
August 19, 2025
Cause-Specific Mortality in Three German Cities’, American Journal of Respiratory Critical Care Medicine, Vol. 10, May 2023)
• “UFPs deposit readily in the airways and centriacinar regions of the lung and induce and incite airway diseases such as asthma and COPD [chronic obstructive pulmonary disease] and respiratory diseases. Oxidant- mediated cellular damage including the production of reactive oxygen species (ROS) and oxidative stress can lead to PM-mediated diverse health effects.” ‘Mechanisms of ultrafine particle-induced respiratory health effects’, Experimental & Molecular Medicine Vol. 52, 2020) “There is a growing body of evidence suggesting UFP may play a bigger role inflicting adverse health effects than has been recognized, and in this perspective, we highlight effects on the brain, particularly of young individuals.” ‘Air Pollution, Ultrafine Particles, and Your Brain’, Environmental Science and Technology, 2022, Vol. 56, by Alberto Ayala [Executive Officer, Sacramento Metropolitan Air Quality Management District])
Sincerely,
_____________________________
Earl Withycombe
_____________________________
Ralph Propper
Attachments:
Résumés of Earl Withycombe and Ralph Propper
Résumé
Earl Withycombe
Education
1970, B.S., Aeronautical Engineering, Massachusetts Institute of T echnology, Cambridge, Massachusetts
1989, Certificate in the Management of Hazardous Materials, University of California, Davis, California
Professional Experience
8/06 to 12/22 Air Resources Engineer
California Air Resources Board
Served as the planning liaison to the South Coast Air Quality Management District, facilitating coordination between ARB and the District in the development of the 2007 8-hour ozone and PM2.5 State Implementation Plan for the South Coast Air Basin. Served as the planning liaison to the Sacramento Metropolitan region, the Mountain Counties Air Basin, and Eastern Kern County. Provided technical oversight to windblown dust issues at Owens Lake, Mono Lake, and the Salton Sea. Served as a member of the Oceano Dunes State Vehicle Recreation Area Scientific Advisory Group, and as a member of the Salton Sea T ask Force’s Science and Air Quality Committees.
5/93 to 6/06 Partner
Sierra Research
4/88 to 5/93 Senior Engineer
Sierra Research
Worked as a partner and project manager in a consulting firm specializing in air quality analysis and management. Experience included management of regulatory development and project evaluation services for governmental clients; management of process, control, and instrumentation design; emission and impact evaluation; and compliance strategy services for private clients. Technical contributions included air quality modeling, combustion modeling, control equipment design and analysis, ambient air quality analysis, ambient and stack sampling project design, screening risk assessment, permit development, and particulate matter and fugitive dust emission factor development services for a variety of projects, including those related to power production, cogeneration, industrial boilers, geothermal activities, mineral extraction and processing, lumber production, toxic waste treatment, fugitive dust, and Superfund remediation.
-2-
7/75 to 4/88 Air Basin Engineer
Mountain Counties Air Basin,
Lake Tahoe Air Basin
Established and managed a consulting practice providing exclusive and comprehensive technical services to an association of nine county air pollution control districts in the Sierra Nevada region of California. Drafted numerous amendments to the air basin plan in implementing federal and state mandates and responding to new local problems. Developed annual budgets for a number of districts. Developed ozone nonattainment plans for El Dorado and Mariposa Counties. Drafted and implemented the first local Prevention of Significant Deterioration program in rural California. Analyzed compliance with emission limits and ambient air quality standards for all major and many minor new and modified source applications within the nine county region. Developed comprehensive stationary and area source emission inventories for the Mountain Counties Air Basin (1977) and for the Lake Tahoe Ozone Nonattainment Plan (1981). Certified all test plans and oversaw all stationary source testing in the Air Basin.
Served as the Co-Chairman of the CAPCOA-ARB New Source Review Rule Committee that developed the 1982 CAPCOA NSR rule which served for many years as a model regulation for the permitting of new sources by districts. Drafted and successfully lobbied several legislative bills amending the relationship between districts and the California Air Resources Board and authorizing experimental programs seeking innovative solutions to air quality problems. Drafted language and lobbied for passage of AB 3374 (1986), the second Calderon landfill testing bill, which refocused priorities on active landfills and adopted more cost effective monitoring protocols for small rural landfills.
8/73 to 1/75 Air Pollution Control Officer
County of Sierra
Served as the program manager of a rural county air pollution control district. Developed and implemented compliance plans for two timber processing facilities. Managed the accounting, budget, reporting, permit review, and air quality monitoring functions of the agency. Developed the technical justification for formation of the Mountain Counties Air Basin to supplant the mountain portions of the Sacramento and San Joaquin Valley Air Basins. Drafted major portions of the first Air Basin Plan and related regulations.
Credentials, Memberships, and Awards
Qualified Environmental Professional, Air Pollution; Institute of Professional Environmental Practice
Registered Civil Engineer, California
Member, Air and Waste Management Association
Outstanding Individual, 1994 Summer Smog Season Campaign, Partners for Clean Air, Sacramento, California
Clean Air Award, American Lung Association of Sacramento-Emigrant Trails, 1996 Environmentalist of the Year Award, Environmental Council of Sacramento, 1997 Pottenger Award for Volunteer Service, American Lung Association of California, 2002
Résumé of
RALPH PROPPER
Education
BA Chemistry, Brandeis University
PhD Chemistry (all but dissertation), University of Chicago MPH Environmental Health, Boston University Medical School
Professional Experience
Toxicology research assistant:
MIT, Stanford University, UC Berkeley, UC San Francisco
Air Pollution Research Specialist, CA Air Resources Board 1984-2015 Focus: Diesel Exhaust regulation, air toxics control
Chemistry Professor, UC Davis and Sacramento City College 2015-2018
Current Board Member, and past board president of both:
* Breathe California Sacramento Region, and
* Environmental Council of Sacramento
Publication
Propper, R., Wong, P., Bui, S., Austin, J., Vance, W., Alvarado, Á., Croes, B., & Luo, D. (2015). Ambient and Emission Trends of Toxic Air Contaminants in California.
Environmental science & technology, 49(19), 11329–11339. https://doi.org/10.1021/acs.est.5b02766
Tricolored blackbird survey methods
June 6, 2024
REVIEW PAPER
Daniel Airola
1 *, Edward C. Beedy
2 , Susan Sanders
3 , and Joseph Medley
4 1
Conservation Research and Planning, Sacramento, CA, USA https://orcid.org/0000-0001-6725-4230
2 Beedy Environmental Consulting, 12213 Half Moon Way, Nevada City, CA 95959, USA 3 AECOM, 2020 L Street, Suite 300, Sacramento, CA 95811, USA 4 USDA Forest Service, Bass Lake Ranger District, 57003 Road 225, North Fork, CA 93643, USA *Corresponding Author: [email protected]
Published 6 June 2024 • doi.org/10.51492/cfwj.110.6
Abstract
Surveys for the tricolored blackbird (Agelaius tricolor), a California-listed threatened species, are needed to provide essential information about its status and distribution to support conservation efforts.
Surveying for the species, however, poses challenges because of its colonial nesting habits, large flock sizes, and frequent interannual movements among colony sites. We present standardized approaches for tricolored blackbird surveys to accommodate a variety of goals, including determining potential for occurrence, detecting colonies, estimating population numbers, and assessing nesting success. Pre- survey research should assess overlap with the species’ geographic range and include database searches for recent and historical occurrences. Site surveys should assess availability of sufficient suitable foraging habitat (grasslands, irrigated pasture, shallow wetlands, agricultural fields) within 5 km of potential nesting habitat and nearby drinking water. Confirming presence or absence of nesting at a historical colony site, or at an area within the range of the tricolored blackbird that provides suitable nesting and foraging habitat, requires at least three surveys conducted about three weeks apart during the breeding season, generally April, May, and June in most of the species’ range. Colonies can be located by searching for foraging flocks and following them to colonies and by checking for nesting activity at suitable nesting substrates, especially those used in the past. Surveyors can estimate numbers from counts of foraging flocks departing and arriving at colonies, average density and area occupied by the nesting colony, and post-nesting density transects. Colony nesting success (i.e., whether a colony successfully fledged some young), is easily determined and is often the only feasible metric to attain on reproduction. Determining reproductive success (the average number of young fledged per occupied nest) may be feasible under ideal and intensive surveys but is impractical at many colonies due to accessibility limitations.
Key words: Agelaius tricolor, breeding, colonial, occurrence, population survey, reproductive success, survey methods, tricolored blackbird
Citation: Airola, D., E. C. Beedy, S. Sanders, and J. Medley. 2024. Tricolored blackbird survey methods.
California Fish and Wildlife Journal 110:e6.
Editor: Shannon Skalos, Wildlife Branch
Submitted: 28 October 2023; Accepted: 29 January 2024
Copyright: ©2024, Airola et al. This is an open access article and is considered public domain. Users have the right to read, download, copy, distribute, print, search, or link to the full texts of articles in this journal, crawl them for indexing, pass them as data to software, or use them for any other lawful purpose, provided the authors and the California Department of Fish and Wildlife are acknowledged.
Competing Interests: The authors have not declared any competing interests.
Introduction
The tricolored blackbird (Agelaius tricolor) was listed as a threatened species under the California Endangered Species Act (CESA) in 2019 because of habitat loss, nest losses to agricultural harvest, and insecticide use (Clipperton 2018; Beedy et al. 2023). The species’ conservation and legal status necessitates surveys and monitoring for a variety of purposes, including monitoring population status, determining potential for land use conflicts, and monitoring effectiveness of conservation actions.
Surveys may also be required to support impact assessments for proposed projects on public and private lands to comply with CESA, the California Environmental Quality Act (CEQA), and other environmental laws and regulations.
A variety of tricolored blackbird survey protocols have been developed for specific purposes, including methods for the statewide tricolored blackbird survey that has been conducted in California since 1994 (Kelsey 2008; Riverside County 2018; Meese 2017; Colibri Ecological Consulting 2022). Here we present standardized methods at various intensities to provide a consistent approach to tricolored blackbird surveys that can be applied throughout the species’ range.
Various types of surveys are applicable depending on goals that may include determining habitat suitability, colony detection, estimating numbers, and assessing nesting status and success. These methods may be employed sequentially, such that a site may first be evaluated for suitability and then, if found to be suitable, surveyed for presence or absence of a colony, colony size, and reproductive success. Some presented methods here, especially for colony detection and estimating numbers, overlap with the approach used in the statewide tricolored blackbird survey (Meese 2017; Colibri Ecological Consulting 2022). However, that one-weekend survey is intended primarily to acquire a statewide population number rather than definitively characterize occupation, numbers of breeders, and breeding success at individual sites, as is our focus here. We focus mostly on surveys for breeding colonies, but also offer advice for conducting surveys for winter-roosting tricolored blackbirds (Table 1).
Table 1. Summary of tricolored blackbird survey methods and key actions for various survey goals.
Survey Goal Method Key Actions
Determining
Potential for
Occurrence
Pre-survey research Check geographic range, general habitat conditions, and elevation
Determining
Potential for
Occurrence
Reconnaissance site visit
and habitat assessment
Review aerial imagery for adequate suitable open
foraging habitatCheck site and nearby areas for
suitable nesting habitat and available surface
water
Detecting Colonies Determining past site use Review historical and recent records in CNDDB, eBird, and Tricolored Blackbird Portal
Detecting Colonies Focused surveys to assess
presence/absence of
nesting colony and suitable
foraging habitat
Conduct at least 3 surveys ~ 3 weeks apart over
the breeding season within 5 km of project
sitesEvaluate suitability of foraging habitat
Detecting Colonies Colony detection surveys Survey known colony sites, suitable nesting habitat, and search suitable open foraging habitat
areas for foraging flocks
Estimating Numbers Direct counts Focus counts on lines of departing and arriving birds during the settlement and nestling
stagesAdjust counts for estimates of birds
remaining in colonies or away foraging.
Estimating Numbers Estimates from passage
rates
Count numbers flying per sample period and
multiply by the duration of departure or arrival
events
Estimating Numbers Estimates from area
occupied
Estimate area of occupied nesting habitat and
multiply by standard density estimates
Estimating Numbers Estimates from nest density
transects
Conduct sample transects after colony fledging
and multiply density by occupied area and by sex
ratio correction factor (0.67)
Estimating Numbers Counting large colonies Generate a collective estimate from multiple observers’ estimates, area occupied, and typical
density
Determining
Nesting Success
Colony success Search for fledged young or presence of feces in empty nests
Determining
Nesting Success
Reproductive success Count fledglings at 4–6-day intervals after first fledglings observedDivide number of fledglings by
the product of number of breeding birds x 0.67 (to
account for 2:1 sex ratio)
Surveying Winter
Roosts
Counts at roosts Count in areas of dense emergent vegetation at duskRecognize that little is known about night
roosting habits and habitats
Determining Potential for Occurrence
Pre-Survey Research
The first step in evaluating the potential for tricolored blackbird occurrence is to examine the species’ geographic range in relation to the site of interest and consult databases for historical and recent records of occurrence. The tricolored blackbird occurs primarily in California (Figure 1), but its geographic range is shown in its entirety by Beedy et al. (2023). Relevant databases include eBird (https://science.ebird.org/en), the California Department of Fish and Wildlife’s (CDFW’s) California Natural Diversity Database (CNDDB; https://wildlife.ca.gov/Data/CNDDB), and the Tricolored Blackbird Portal (https://tricolor.ice.ucdavis.edu/).
Figure 1. Tricolored blackbird breeding and year-round range in California. (Map created by AECOM) The species’ geographic range generally occurs in regions with extensive open grasslands and agricultural lands. Most colonies occur at lower elevations (e.g., primarily below 200 m elevation in the Central Valley and adjacent foothills), but where suitable conditions exist, nesting can occur at elevations up to 1,200 m in the foothills of the Sierra Nevada. Transverse Ranges, and Coast Range (Airola et al 2023a; Beedy et al. 2023).
Reconnaissance Site Visit and Habitat Assessment
If the survey or project area is within the range of tricolored blackbirds, aerial imagery (e.g., Google Earth) should be reviewed to assess whether extensive foraging habitat is available within 5 km of the project area. Tricolored blackbird foraging flight distances vary considerably over the course of a breeding season due to shifting food availability and the nutritional demands of nestlings and fledglings.
Most foraging occurs within 1 km from colony sites, but adults have been recorded foraging up to 8.6 km away(Hamilton and Meese 2006). We consider 5 km from the nesting colony as the most relevant distance within which to assess habitat conditions because it is consistent with typical foraging distances reported (Orians 1961; Crase and DeHaven 1977; Hamilton and Meese 2006; Wilsey et al. 2019; Airola et al. 2023a).
In the Sierra Nevada foothills where concentrated food sources such as feed lots, dairies, and organically farmed rice fields are mostly absent, areas in which at least 60% of the area within 5 km (i.e., 2,400 ha) support suitable foraging habitat (described below) could support a tricolored blackbird colony (Airola et al. 2023a) and warrant reconnaissance surveys. The minimum amount of foraging habitat to support colonies is not well documented in other portions of the species’ range, but we recommend reconnaissance surveys there if several hundred hectares of suitable foraging habitat, and especially concentrated food sources, are present within 5 km of a project site. Although tricolored blackbirds have modified their foraging and nesting behaviors to accommodate anthropogenic habitat changes within their range, certain key habitat components described below must be present to support nesting colonies, including suitable foraging and nesting habitat and surface water for drinking and bathing (Meese and Beedy 2015).
Open Foraging Habitat and Concentrated Food Sources.—Tricolored blackbirds are birds of open habitats that forage almost entirely on the ground for seeds and invertebrates. They generally prefer to feed as near as possible to colonies, but regularly travel up to 5 km (and infrequently up to 10 km) from colonies to exploit concentrated food sources.
Suitable foraging habitat generally consists of grazed grasslands, irrigated pasture, shallow wetlands, and agricultural fields, especially fields with annual seed crops such as rice (particularly organic crops), alfalfa, ripening or cut oats, milk-stage barley, wheat, and storage bins of livestock food (Crase and DeHaven 1977; Skorupa et al. 1980; Meese 2013; Beedy et al. 2023). Tricolored blackbird colonies require large quantities of insects to feed their young. Nestlings are fed almost entirely insects for the first nine days after hatching (Skorupa et al. 1980), so colonies depend on dense concentrations of invertebrate prey such as grasshoppers, lepidoptera larva, and flies, including those produced in dairy operations (Goodward and Diaz 2023), to meet protein-rich food requirements. Denser concentrations of invertebrate prey tend to occur in small portions of the overall suitable foraging habitat and are often ephemeral, thereby necessitating multiple foraging sites over the course of a nesting season and in different years. As a result, tricolored blackbirds require large areas of suitable foraging habitat within which they can find these food-rich areas.
Airola et al. (2023a) found a strong relationship between the amount of suitable foraging habitat with a 100 km
2 area and the probability of colony occurrence in the grasslands of the Sierra Nevada foothills.
Colonies were most likely to occur where at least 80% of the area within 5 km of a potential colony site contained suitable foraging habitat, and no areas where foraging habitat comprised less than 60% were used for nesting. Because patch sizes of nesting habitat used may be so small as to not be mapped in existing vegetation mapping data (Airola 2021), areas that support extensive foraging habitat with concentrated prey sources and suitable nesting habitat within 5 km should be assumed to have potential for occurrence of tricolored blackbirds unless otherwise determined.
Suitable Nesting Habitat.—Tricolored blackbirds nest in a variety of vegetation types, but most breeding colonies occur in emergent cattail (Typha sp.) and tule (Schoenoplectus sp.) marshes, non-native Himalayan blackberry (Rubus armeniacus), and agricultural fields, especially triticale (Triticum X Secale) grown for dairy silage (Meese and Beedy 2015; Airola 2021; Beedy et al. 2023; Castañeda et al. 2023).Patch sizes of nesting habitat used by tricolored blackbirds may be very small (i.e., 0.04–1.1 ha; Airola 2021) and therefore may not be depicted in existing large-scale vegetation mapping data. Most areas that support extensive foraging habitat provide an adequate amount of nesting habitat to support colonies, but its availability should be verified.
Water.—Surface water for daily drinking and bathing is a key habitat requirement (Wilsey et al. 2019; Beedy et al. 2023). A variety of water sources are used, including natural streams and wetlands and vernal pools in grasslands, as well as anthropogenic sources such as farm and field ditches, flood irrigation, irrigation sprinklers, and drip irrigation (Beedy et al. 2023). Little quantitative information on distance from nesting areas to water is available, but some colonies at dairies or in uplands (especially milk thistle [Silybum marianum]) may be >100 m from the nearest water (Beedy et al. 2023). Many plants used as nesting habitat, including cattail, tule, and Himalayan blackberry, are associated with open water or saturated soils (Meese and Beedy 2015; Wilson et al. 2016; Airola 2021) or regular irrigation (triticale and other crops; Castañeda et al. 2023), which typically provide a nearby water source. Therefore, most areas that support suitable nesting habitat are also likely to provide adequate drinking water.
In summary, the most important criterion for determining whether a site containing potential nesting habitat could support a tricolored blackbird colony is the presence of an adequate amount of suitable foraging habitat within 5 km of suitable nesting habitat. Areas with adequate foraging habitat will generally, but not always, provide adequate nesting habitat and drinking water and thus could potentially support a nesting colony.
Detecting Colonies
Determining Past Site Use
Some survey efforts may seek to determine if a nesting colony is present or if it could be present at a site in the future. In addition to evaluating suitability based on existing habitat conditions, potential colony sites can be identified from past records of occurrence at or near a site. Tricolored blackbirds are itinerant breeders and often rotate colony locations among different sites in a region (Airola et al. 2023a).
Breeders tend to be philopatric to more than one site (Hamilton 1998); banding studies found that nearly one-fourth of 2,972 recaptured birds were recaptured in the same location where they were banded and nearly 40% were recaptured in the same county (Beedy et al. 2023). Colony sites in the Sierra Nevada foothills, mostly in patches of Himalayan blackberry, were occupied in subsequent years only about 50% of the time, although the birds appeared to relocate to other nearby areas and often returned to previously used sites in later years (Airola et al. 2018). Colony sites may shift in response both to changes in the abundance of preferred prey and interannual differences in nesting habitat suitability (Graves et al. 2013; Airola et al. 2016). Therefore, the presence of a past colony indicates a likelihood of future re-use of the site or a nearby area if it retains suitable nesting and foraging conditions.
Locations of previously used colony sites are available from CNDDB and the Tricolored Blackbird Portal.
Of course, not all past colony sites have been found, in part because many areas with suitable habitat are inaccessible on private lands. Also, over time new areas of suitable nesting habitat become available due to changes in maintenance or farming practices, rainfall, and growth of nesting substates. Conversely, previously occupied, and suitable areas can become unsuitable especially due to land uses change (i.e., development or conversion to crops such as orchards and vineyards that are unsuitable for foraging and breeding (Cook and Toft 2005; Airola et al. 2023a,b). Therefore, the current suitability of previously occupied sites needs to be verified by focused surveys.
Focused Surveys to Assess Presence/Absence of a Nesting Colony and Foraging Habitat
To comply with CEQA assessment requirements or certain permit conditions (e.g., a CDFW Lake and Streambed Alteration Agreement) it is often necessary to determine if a proposed project site supports an active tricolored blackbird nesting colony or provides foraging habitat that is important to a nearby active colony. If the proposed project site is near a historical nesting record it may also be necessary to confirm whether that site is occupied or unoccupied.
To assess nesting presence or absence at a historical colony site, or at an area within the range of the tricolored blackbird that provides suitable nesting and foraging habitat, at least three surveys should be conducted approximately three weeks apart during the breeding season (Table 2). Surveys should cover suitable habitat within the entire project area and an area within 5 km of the proposed project area, at least to the extent to which access permission can be acquired or lands can be viewed from publicly accessible or authorized areas. Surveys should be conducted by biologists who are experienced in identifying tricolored blackbirds by sight and sound, and knowledgeable about their biology, especially about the habitat types needed for foraging and nesting and foraging behavior.
Table 2. Tricolored blackbird nesting periods by region.
Region Nesting Period Source
Baja California Late March – Early June Erickson et al. 2021 Southern California Late March – Early June Beedy et al. 2023 San Joaquin Valley and adjacent
areas
Late March – Early June Beedy et al. 2023
Region Nesting Period Source
Central California coast Early April – early July Wilson et al. 2016 Central Sierra Nevada foothills Early April to Late June Airola et al. 2015; D. Airola unpublished data
Sacramento Valley Early April – Mid-August Orians 1961; Colibri Ecological Consulting 2022
Northeastern California and Nevada Mid-April – Mid-August Extrapolated from other locations Oregon and Washington Early April – Mid-August Gilligan et al. 1994; McCormick 2022 Typically, colony surveys should occur in April, May, and June (Table 2), but in more northerly locations the last of the three surveys should start later and may need to extend to mid-August. In more southerly locations nesting may be initiated as early as March, and even exceptionally in February in the southern San Joaquin Valley (Beedy et al. 2023). Notably, under recent warming climate conditions, breeding is occurring earlier, so the timing of breeding may continue to shift toward earlier dates. The timing of nest initiation by different colonies in a small region may vary by as much as six weeks during a single year, and the timing of nesting may vary among years by up to three weeks or more depending on weather (D.
Airola, unpublished data).
Three surveys spread throughout the tricolored blackbird nesting season will adequately cover the typical 41–45-day breeding period for a successful nesting pair (Table 3; Beedy et al. 2023) and variation in timing of breeding (Table 2). Understanding of tricolored blackbird nesting phenology and behavior, and resulting detectability, is important for conducting effective surveys. Incubating females are typically silent while on the nest during incubation, and males often remain inconspicuous, so active colonies may appear to be largely deserted then. Smaller and highly synchronous colonies are especially inconspicuous during this period and may be overlooked or their size underestimated (Beedy et al. 2023).
Table 3. Tricolored blackbird breeding phenology
a
.
Activity Duration Comments
Colony
Prospecting and
Pair Formation
12–17 days
before nesting
building begins
Males typically arrive before females and perch conspicuously on top of vegetation; may begin singing as early as late February; most males mate with two females.
Nest Building Average 4 days,
range 3–5 days
Timing of nest building may vary within colony, so may
extended beyond the per-nest duration reported here.
Egg Laying 1 egg laid/day for
1–5 days
Egg-laying may begin as early as the 2
nd
day after nest
initiation but typically starts about 4 days after settlement.
Clutch size typically 3–4.
Incubation 11–12 days Only females brood and begin incubating with laying of last egg or on the next day. Females are mostly silent on nest, while males perch inconspicuously below vegetation or away from colony.
Activity Duration Comments
Nestlings 9–10 days Males and females feed nestlings; mean interval for foraging trips varies but is about 15 min for females, 30 min for males.
Fledging 11–14 days By day 4 after fledging, young fly to trees or other tall vegetation within 500 m of colony. By day 6, young typically disperse from colonies and join adults to fly to water and foraging areas.
a
Sources: Orians 1961; Payne 1969; Beedy et al. 2023
Nesting can extend beyond the typical 41–45-day period for several reasons. Newly arrived pairs may join a colony for up to several weeks after colony establishment and so nesting phenology may vary within a colony (Beedy et al. 2023; Wilson et al. 2016). Also, adults may breed twice or even three times at a colony site if conditions are favorable (Schackwitz et al. 2020; Beedy et al. 2023).
The presence/absence conclusions from the surveys are applicable only to the year in which they were conducted. If construction or other nest-disturbing activities are proposed to occur in years after the survey, then the focused surveys described above should be repeated.
Colony Detection Surveys
Colonies are generally located in two ways: 1) searching for foraging flocks and then following them to colonies and 2) checking known and suitable nesting habitats.
Search for foraging flocks.—Tricolored blackbird flocks tend to occur in two different configurations during the breeding season: as migratory or pre-settling flocks and as foraging flocks from colonies.
Because of their itinerant breeding pattern (i.e., tendency to nest more than once per year at different locations, first in the south and then further north; Hamilton 1998), migratory or prospecting flocks regularly move through breeding habitats during the breeding season in search of suitable nesting areas or while on their way to other breeding areas to the north. Migratory or non-breeding tricolored blackbirds tend to fly in a distinctive “wing-tip to wing-tip” flock structure that is wider than it is long.
In contrast, tricolored blackbirds associated with colonies fly in long lines (or “strings”) between the colony site and foraging areas. Foraging flocks from colonies also tend to fly lower than migrating or prospecting flocks. These flocks are relatively easy to locate in areas with adequate access (i.e., from public roads) and open, visible conditions because of their size and cohesion. Flocks can often be seen as far away as 1.5 km (Airola et al. 2015) and can readily be tracked to their nesting site if it is visible and accessible. Many areas of potential habitat, however, are on inaccessible private lands or not visible due to topography and vegetation screening.
Direct Searching for Colonies.—A second strategy for locating colonies is to check suitable nesting substrates, especially previously used ones. Occupancy can often be determined at sites from the loud song choruses early in the season (Schackwitz et al. 2020; Beedy et al. 2023; Honig and Schackwitz 2023), swarming activity during settling and nest building, and by observing adults returning to colonies with food for nestlings. A caution for direct observation is that activity can be very low during the incubation period, such that activity at occupied colonies may be subtle and detected only by experienced observers or in later visits.
The statewide survey, typically conducted on one weekend every three years (Meese 2017; Colibri Ecological Consulting 2022), checks past colony locations and locates new colonies while travelling between previously used sites. The statewide survey, however, is intended to estimate the statewide population, and results are not always definitive in determining whether individual surveyed sites are active or inactive because sites occupied during the one-time surveys may be abandoned before nesting begins, or unoccupied sites may become active after the survey date (Airola et al. 2023b).
Estimating Numbers
The tricolored blackbird forms the largest colonies of any North American passerine. Breeding colony sizes range from several hundred to tens of thousands of individuals (and historically hundreds of thousands; Neff 1937). Colonies of 15,000–25,000+ have been recorded in dairy silage fields in recent years (Colibri Ecological Consulting 2022), as numbers have started to rebound in the San Joaquin Valley (Castañeda et al. 2023), although colony sizes in the Sierra Nevada foothills generally average 1,500–2,500 birds (Airola et al. 2023b).
Determining numbers of tricolored blackbirds at nesting colonies is challenging for several reasons. The occurrence of birds in large numbers presents its own counting challenge. Dense nesting substrates impedes visibility, and the long-distance movements from colonies to foraging areas (regularly up to 5 km) means that at any given time a substantial proportion of the colony may not be present to be counted at the colony site. Thus, colony size estimation is an inexact science, with estimates typically believed to be within a range of 20% above or below actual values (Castañeda et al. 2023).
Despite the limitations on counting, reasonably accurate counts can be made by applying one or more of several methods alone or in combination. The main methods include direct counts, estimates from passage rates, and area counts (Audubon California 2008; Colibri Ecological Consulting 2022). Ideally, multiple counts and methods should be used and then compared to produce the best possible estimate.
Counting accuracy can be improved through practice, by estimating numbers of tricolored blackbirds or other species or objects in the field and then counting them. Surveyors also can take photos of large flocks, estimate numbers, and then count numbers in the image and compute count-biases that can be used to adjust field estimates (Fulton and Kajrys 2019).
Direct Counts
Direct counts are best conducted during settlement and nestling stages when birds typically leave the colony sequentially in “lines” of birds to foraging areas and then return in lines to the colony. Departures from colonies often occur over a period of 5–20 minutes or can be continuous, with birds coming and going multiple times to feeding areas. Departure rates vary depending on the size of the colony at rates of <1/sec to 50, 100, or even more birds per second.
Under these circumstances, counts are best made by waiting for birds to return to the colony, finding a lull in returns, and then counting departing birds by fives, 10s, 20s, 50s, or 100s (depending on the number of birds departing; Fulton and Kajrys 2019). At times, nearly all colony occupants may depart before any birds return. At other times, a substantial proportion of birds depart, while others remain at the colony. Finally, some birds often may begin returning to the colony before all birds have left, creating a challenge in deciding when to terminate counts to avoid double counting those birds that leave, return, and then leave again. One can also choose to count only arriving birds using the same procedures as for departing birds.
Counting departing birds provides a minimum estimate of numbers. The count can then be adjusted intuitively to account for birds that appear to have remained at the colony or those that may have left before the count was initiated. The result is an estimate, not an exact count, but one that is better than a simple guess or an order-of-magnitude approximation.
Estimates from Passage Rates
Using passage rates to estimate numbers has been included in several previous protocols (Audubon California 2008; Colibri Ecological Consulting 2022). This method is similar to direct counts, but it samples departing or arriving birds for a prescribed period and multiplies the passage rate by the duration of flights to calculate an abundance estimate. Using passage rates is problematic because the rates of departure or arrival at colonies are seldom uniform. Since the use of passage rates requires remaining at the site throughout the flight period to determine the duration of flights, it is relatively easy and more accurate to just count continuously throughout the flight period. Therefore, we do not recommend using passage rates as an estimation method.
Estimates from Area Occupied
This method involves mapping the area occupied by nesting birds (e.g., using Google Earth) and multiplying the area by an average density. This method relies on a critical assumption about nest spacing within colonies. Some colonies nesting in Himalayan blackberry have nesting densities of up to 6 nests/m
2 , and a colony in Tulare County nesting in a triticale field had up to 12 nests/m 2 (Beedy et al.
2023). The average nest density in colonies in the Sierra Nevada foothills, however, is only 0.45/m 2 (D.
Airola, unpublished data). In applying this method, it is important not to simply assume that all suitable habitat at a site is occupied, but rather to verify which area(s) are occupied by observing singing, arriving, and departing birds. With experience, a sense of likely population based on size of occupied area can be a useful check on estimates made through direct counts.
Estimates from Nest Density Transects
Conducting nest transects to determine numbers of breeders can be effective but has limitations.
Transect counts of nests are used to calculate nest densities of known sampled area, which is then applied to the entire area occupied by the colony to estimate a colony total. Nest counts can only be made after confirming that all nesting activity has been completed to avoid disturbing active nests and causing nest abandonment because nestlings will jump from nests when disturbed (Payne 1969; Kyle and Kelsey 2011). Triticale is typically very dry after nesting and often flattened or harvested, impeding nest detection and resulting in underestimates. The nest-transect method also can only be conducted in accessible nesting substrates (i.e., not in the dense, spiny Himalayan blackberry). Transects should record only those nests that show signs of having been used (presence of unhatched eggs, nestling feces) as tricolored blackbirds often will construct and then abandon nests before egg-laying. The number of nests is converted to number of breeders by multiplying by 1.5, to reflect the typical male to female sex ratio of 1:2 in colonies (Orians 1961; Payne 1969).
Counting Large Colonies
Counting colonies with more than 5,000 individuals is especially challenging because of the difficulty in estimating the sizes of multiple large groups of birds leaving and returning to the colony, often simultaneously from different directions. General guidelines for counting large colonies are as follows:
Generate a “collective” estimate based on multiple observations throughout the colonization, settlement, incubation, nestling, and fledging stages. Keep a rough estimate of colony size at each visit and update the estimates as the colony grows or contracts.
Estimate numbers in the morning when lighting is favorable and before temperatures rise and create heat waves. Avoid counting in windy or rainy conditions when birds may remain hidden in cover in silage or other vegetation.
Be aware of random events, such as a predator or a large airplane flying over, that may cause large groups of birds to flush and fly, and use such occasions to conduct counts.
Conduct surveys with at least two experienced observers who work together to develop an estimate.
Multiple surveyors observing from different vantages can regularly communicate what they are seeing and then confer when estimates differ. This collaborative approach fosters discussions as to why differences in estimates might have occurred and whose observations are most complete and allows readjustment of estimates.
Large flocks of birds in flight are commonly undercounted and the extent of undercounting typically increases as flock size increases. Fulton and Kajrys (2019) describe several techniques to address and compensate for the undercount bias in large flocks.
Perform nest transect counts, where feasible, and calculate numbers independently based on the occupied area.
Determining Nest Success
Two measures can be used to describe nesting success of colonies: colony success and reproductive success (also often referred to as “productivity”).
Colony Success
Colony success describes whether a colony successfully fledged at least some young. This measure is general but is easy to determine and often may be the best information that can be determined for a colony. Colonies are considered successful when fledglings are observed at or near the colony or feces are seen in an empty nest. Monitoring via vocalizations also can be used to determine if young have reached fledgling age (Schackwitz et al. 2020; Beedy et al. 2023; Honig and Schackwitz 2023). Less direct evidence that indicates that a colony was likely successful includes repeated observations of adults feeding young at the colony over a 10-day period (Table 3; Beedy et al. 2023).
Bioacoustic monitoring is a new tool that can provide detailed information on reproductive phenology and breeding success of tricolored blackbird colonies (Schackwitz et al. 2020; Honig and Schackwitz 2023).
The technique involves recording tricolored blackbird colonies and analyzing them to detect the timing of six vocalizations—male song, male chorus, female song, hatchling call, nestling call, and fledgling call (Honig and Schackwitz 2023). These calls provide detailed information about breeding phenology and success, including dates of courtship; onset of nest building, incubation, and nestling hatching; and fledgling departure from nesting colonies. The tool assesses colony success or failure and numbers of separate nesting cohorts (or “waves”) while avoiding colony disturbance from frequent nest colony visits.
The method is currently used mainly for testing and research but may be more widely available soon to determine project-related needs such as for determining when colonies have completed nesting (W.
Schackwitz, pers. comm.).
Reproductive Success
Reproductive success is defined as the average number of young fledged per occupied nest. Determining reproductive success of tricolored blackbird colonies is challenging, and in fact impractical at many colonies for several reasons. First, nests should not be inspected while adults and young are present (i.e., to count young close to fledgling age) to avoid disturbance, premature fledging, abandonment, and resulting nestling mortality. Also, many colony sites are not accessible to count fledglings because of lack of access to private lands. Even where colonies are accessible, nestling, and fledgling counts are often impeded by the impenetrability of the nesting substrate (i.e., in Himalayan blackberry or dense, flooded cattails or tules) or limited visibility of the entire surface of the vegetation within which fledglings may be perched. Placing video cameras to monitor nests can cause disturbance, and it is often impractical to place enough recorders to accurately characterize an entire colony. Visibility for drone surveillance is impeded by foliage and could disturb active nests. Monitoring via vocalizations can determine if fledglings are present but cannot be used to estimate fledgling numbers (Schackwitz et al. 2020). As a result of the challenges of avoiding colony disturbance during surveys and the potential inaccuracy of results, many researchers do not attempt to go beyond determining colony success.
Notwithstanding the challenges, the best available method for determining reproductive success involves direct counting of fledglings in and around the colony as they wait to be fed by adults. Multiple counts, however, are required because fledging at a colony may occur over a period of up to several weeks. In general, fledglings are believed to remain at the colony site for an average of four days after fledging (Beedy et al. 2023). By day 6, young typically disperse from colonies to fly to water and foraging areas.
Fledglings from colonies in isolated triticale fields or other nest substrates lacking nearby tall vegetation do not show this developmental sequence and may remain in a colony for at least 2 weeks before making their first long-distance flight (Beedy et al. 2023). Thus, fledgling counts should be conducted every four to six days (starting with the first observation of fledged young) until they are no longer present.
Reproductive success is then calculated by the equation:
Average number of young/nest = # fledglings / (# breeding birds x 0.67 nests/breeding bird) The 0.67 nests per breeding coefficient incorporates the fact that most males breed with two females (Orians 1961; Payne 1969).
Surveying Winter Roosts
Studies of winter roosting by tricolored blackbirds are in their infancy. A few roosts have been detected recently in Butte and Sacramento counties, but it is unknown if they are longstanding or only recently been established (R. Meese, unpublished data; Beedy et al. 2023). The functions and benefits of winter roosts are unknown but may include reducing metabolic demands (based on their location near water which remains warmer than land on cold nights), maintaining social cohesion, and predator detection and avoidance.
Knowledge of the specific characteristics of roosts and of roost use is incomplete. Roosts in Sacramento County have been in dense, flooded emergent wetlands within suburban areas in Folsom and along the American River Parkway, but they could occur in a variety of other settings. There is little information for use in predicting where roosts are likely to occur.
Counting roosting tricolored blackbirds has its own set of challenges. Birds sometimes circle and stage before entering the roost, but they may also arrive at roost sites near dusk and dive immediately into dense cover. Also, sometimes other species, especially red-winged blackbirds (Agelaius phoeniceus), Brewer’s blackbirds (Euphagus cyanocephalus), and European starlings (Sturnus vulgaris) roost with them. The best method to estimate numbers is to count groups as they arrive, usually by 10s, 100s, or 1000s.
Conclusion
This tricolored blackbird survey methodology identifies standardized approaches to serve a variety of purposes, including determining potential for occurrence of nesting colonies, detecting colonies, estimating population numbers, and assessing nesting success and winter roosts. It also provides a starting point for testing and improving survey methods. Application of these methods should improve our understanding of tricolored blackbird distribution, abundance, reproduction, and habitat selection and thus contribute to the protection of the species and its habitat from the wide range of existing threats (Meese et al. 2015; Airola et al. 2023a,b; Beedy et al. 2023). California’s tricolored blackbird populations would also benefit by development of standardized guidance for avoidance and minimization measures to protect nesting colonies and by creation of a statewide framework for compensatory mitigation to offset the ongoing loss of tricolored blackbird nesting and foraging habitat.
Acknowledgments
Thanks to the many tricolored blackbird researchers and monitors who have contributed to refinement of survey methods over the years, including W. J. Hamilton III, R. Meese, N. Clipperton, S. Fraser, J. Harris, C.
Swarth, D. Ross, W. Schackwitz, E. Graves, R. Cook, R. Erickson, X. Castañeda, S. Arthur, J. Davis, J.
Baum, and C. Conard. Thanks also to AECOM and L. Clement for preparing the Figure. We thank anonymous reviewers and Shannon Skalos for review comments. We gratefully acknowledge BirdLife International and the Cornell Lab of Ornithology for providing the shapefiles from the Birds of the World tricolored blackbird account we used to create the range map.
Literature Cited
Airola, D. A. 2021. Importance of non-native Himalayan blackberry as nesting habitat for the tricolored blackbird in the Sierra Nevada foothills, California. Central Valley Birds 24:1–14.
Airola, D. A., T. Collins, M. Lozano, C. McColl, B. J. Furnas, and D. R. Krolick. 2023a. Foraging habitat and its effects on tricolored blackbird distribution and abundance in the Sierra Nevada foothills, California.
Western Birds 54:19–31.
Airola, D. A., J. Harris, C. Conard, L. A. Douglas, and E. C. Beedy. 2023b. Breeding population status of the tricolored blackbird in the foothills of the central Sierra Nevada, 2014–2022. Central Valley Birds 26:53–68.
Airola, D. A., R. J. Meese, E. C. Beedy, D. Ross, D. Lasprugato, W. Hall, C. Conard, C. Alvarado, J. Harris, M. Gause, L. Pittman, K Smith, L. Young, and J. Pan. 2015. Tricolored blackbird breeding status in 2015 in the foothill grasslands of the Sierra Nevada, California. Central Valley Bird Club Bulletin 18:96–113.
Airola, D. A., C. W. Swarth, J. Harris, E. C. Beedy, G. Woods, K. Smith, D. Ross, and D. Lasprugato. 2018.
Breeding status of the tricolored blackbird in the foothill grasslands of the Sierra Nevada, California.
Central Valley Bird Club Bulletin 21:1–24.
Airola, D. A., D. Ross, C. Swarth, R. J. Meese, D. Lasprugato, and M. L. Marshall. 2016. Breeding status of the tricolored blackbird in the grassland-dominated region of the Sierra Nevada, California in 2016.
Central Valley Bird Club Bulletin 19:82–109.
Airola, D. A., R. J. Meese, and D. Krolick. 2015. Tricolored blackbird conservation status and opportunities in the Sierra Nevada foothills of California. Central Valley Bird Club Bulletin 17:57–78.
Audubon California. 2008. 2008 Tricolored blackbird survey protocol. Audubon Society, Sacramento, CA, USA.
Beedy, E. C., W. J. Hamilton, III, R. J. Meese, D. A. Airola, W. S. Schackwitz, and P. Pyle. 2023. Tricolored blackbird (Agelaius tricolor) version 2.0. In P. G. Rodewald and B. K. Keeny, editors. The Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA.
Cook, L. F., and C. A. Toft. 2005. Dynamics of extinction: population decline in the colonially nesting tricolored blackbird Agelaius tricolor. Bird Conservation International 15:73–88.
Castañeda, X., N. Clipperton, D. A. Airola, S. Arthur, and P. Sousa. 2023. Effectiveness of recent public- private efforts to protect tricolored blackbird breeding colonies on agricultural lands in the San Joaquin Valley, California. Western Birds 54:2–18.
Clipperton, N. 2018. A status review of the tricolored blackbird (Agelaius tricolor) in California. Report to the Fish and Game Commission. California Department of Fish and Wildlife, Sacramento, CA, USA.
Colibri Ecological Consulting. 2022. 2022 tricolored blackbird statewide survey. California Department of Fish and Wildlife, Sacramento, CA, USA.
Crase, F. T., and R. W. Dehaven. 1977. Food of nestling tricolored blackbirds. Condor 79:265–269.
Erickson, R. A., H. de la Cueva, and B. B. Zarmora-Herdandez. 2021. Requiem for the tricolored blackbird in Mexico? Western Birds 52:207–221.
Fulton, J., and G. Kajrys. 2019. The art of counting: how to estimate flock sizes. Central Valley Birds 22:16–24.
Gilligan, J. D., M. Rogers, A. Smith, and A. Contreras. 1994. Birds of Oregon: Status and Distribution.
Cinclus Publications, McMinnville, OR, USA.
Goodward, D. M., and R. A. Diaz. 2023. Tricolored blackbirds’ reliance on insects from dairies. Western Birds 54:181–195.
Graves, E. E., M. Holyoak, T. R. Kelsey, and R. J. Meese. 2013. Understanding the contribution of habitats and regional variation to long-term population trends in tricolored blackbirds. Ecology and Evolution 3:1–14.
Hamilton, III, W. J. 1998. Tricolored blackbird itinerant breeding in California. Condor 100:218–236.
Hamilton, III, W. J., and R. J. Meese. 2006. Habitat and population characteristics of tricolored blackbird colonies in California: 2005 final report. California Department of Fish and Game, Sacramento, CA, USA.
Honig, M., and W. Schackwitz. 2023. Manual versus semiautomated bioacoustical analysis methods of multiple vocalizations in tricolored blackbird colonies. Journal of Fish and Wildlife Management 14:225–238.
Kelsey, R. 2008. Results of the tricolored blackbird 2008 census. Landowner Stewardship Program, Audubon California, Winters, CA, USA.
Kyle, K., and R. Kelsey. 2011. Results of the 2011 tricolored blackbird statewide survey. Audubon California, Sacramento, CA, USA.
McCormick, A. J. 2022. The tricolored blackbird in Washington state: a first assessment of status and distribution. Western Birds 53:186–198.
Meese, R. J. 2013. Chronic low reproductive success of the colonial tricolored blackbird from 2006 to 2011. Western Birds 44:98–113.
Meese, R. J. 2017. Results of the 2017 tricolored blackbird statewide survey. University of California, Davis, and California Department of Fish and Wildlife, Sacramento, CA, USA.
Meese, R. J., D. A. Airola, E. C. Beedy, and R. Cook. 2015. Recovering the tricolored blackbird in California. Central Valley Bird Club Bulletin 17:97–109.
Meese, R. J., and E. C. Beedy. 2015. Managing nesting and foraging habitats to benefit breeding tricolored blackbirds. Central Valley Bird Club Bulletin 17:79–96.
Neff, J. A. 1937. Nesting distribution of the tri-colored red-wing. Condor 39:61–81 Orians, G. H. 1961. The ecology of blackbird (Agelaius) social systems. Ecological Monographs 31:285–312.
Payne, R. B. 1969. Breeding seasons and reproductive physiology of tricolored blackbirds and red- winged blackbirds. University of California Publications in Zoology 90:1–137.
Riverside County. 2018. 2018 Tricolored blackbird survey protocol. Western Riverside County Multispecies Habitat Conservation Plan Biological Monitoring Program. https://www.wrc-rca.org/species/survey_protocols/2018_Tricolored_Blackbird_Survey_Protocol .pdf
Schackwitz, W. S., D. A. Airola, A. Greene, and J. Woodruff. 2020. Bioacoustic monitoring reveals details of tricolored blackbird breeding phenology. Journal of Fish and Wildlife Management 11:518–530.
Skorupa, J. P., R. L. Hothem, and R. W. DeHaven.1980. Foods of breeding tricolored blackbirds in agricultural areas of Merced County, California. Condor 82:465–467.
Wilsey, C., N. Michel, K. Krieger, L. Taylor, L. Lee, S. Arthur, and N. Clipperton. 2019. Defining spring foraging habitat and prioritization of conservation sites for tricolored blackbirds in California. Condor 121:1–13.
Wilson, C. R., R. J. Meese, and A. C. Wyckoff. 2016. Breeding chronology, movements, and life history observations of tricolored blackbirds in the California Central Coast. California Fish and Game 102:162–174.