The tricolored blackbird is very vulnerable to drought because it has historically depended on freshwater wetlands for breeding and relied on large populations of rainfall-dependent insects as prey to feed thousands of young in large breeding colonies. . The tricolored blackbird forms the largest breeding colonies of any land bird in North America, a distinction once held by an extinct species (the passenger pigeon). A three-year count of all known breeding colonies revealed an observed decline of more than 60% over a six-year period (from 395,000 birds in 2008 to 145,000 birds in 2014). The tricolored blackbird's distribution is limited primarily to California, where more than 95 percent of the world's population breeds in the state. The Central Valley has always been the stronghold of this species and the largest breeding colonies of this very social species continue to be found in the valley.
Historically, the Breeded Blackbird tricolor It roamed in huge colonies in the natural freshwater marshes of the Central Valley and hunted insect prey in the surrounding landscapes of prairie and other upland habitats to suit its needs. Over time, the amount of natural habitat suitable for breeding has decreased due to anthropogenic conversion of wetland and upland habitats to other land cover types, including agricultural and urban areas, as well as limited water resources to maintain the Wetland habitat during the drier spring and summer. . month. The tricolored blackbird has adapted to the use of alternative nesting substrates (as well as other wet habitats), and in recent decades the largest breeding colonies have emerged in agricultural cereal fields (primarily triticale, a hybrid grain of wheat and rye grown for feed dairy cattle). . ) in the southern Central Valley.
Need to monitor drought-related stressors
The Department's approach to monitoring and conservation of stressors related to three-colored robin drought will expand studies of breeding colonies, work with the Natural Resources Conservation Service (NRCS) and other partners to protect known breeding colonies, conduct research on the effects of drought on blackbird habitat, and on the reproductive success of tricolores and will determine the best habitat conservation and management options and implement initial projects designed to restore habitats to benefit the species and improve habitat resilience.
With the change in habitat use due to large-scale breeding of colonies in agriculture In cereal fields, a conflict has arisen between tricolored blackbird breeding and harvesting. The breeding season coincides with the harvest season and, in recent decades, thousands of nests, eggs and young have been lost when fields were harvested before the reproductive cycle was complete (Figures 4 and 5). Since the location of breeding colonies changes each year, annual colony surveys should be conducted so that efforts can be made to protect colonies found in agricultural fields. Due to the current drought, the amount of natural wetlands available for tri-colored blackbirds to breed has become even more limited, leaving much of the population to rely heavily on agricultural sites for nesting. This led to a greater need for protection of these large colonies.
Breeding colonies of the tri-colored blackbird use a relatively narrow range of nesting substrates, including wetlands, triticale fields, and some other upland habitats, and also require an extensive foraging landscape and a large source of 'waterfall. productive (within about 3 miles). position of the colony) to take care of the colony's young (Figure 6). Although these requirements for breeding habitat are well established, there is little information on the amount, type, and configuration of food habitat needed to support a thriving colony. Further research is needed to characterize the landscape around colony sites and to evaluate the impacts of these landscapes on the occupancy, size, and success of breeding colonies.
A high long Long-term priority The conservation of the tricolored blackbird involves the creation of alternative breeding habitats to remove colonies from agricultural fields, thus avoiding conflicts with farms and improving the population's resilience to the impacts of other environmental stressors, like drought. The best options for habitat protection and restoration can be based on the research and mapping activities described above.
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Monitoring stressor-related efforts
Colony Detection, Monitoring, and Protection:
CDFW has hired Dr. Bob Meese (UC Davis) and consulting biologist Scott Frazer (ret.). USFWS) to conduct regular surveys in the Central Valley during the breeding season. Following the discovery of the tricolored blackbird breeding colonies, all known locations of the colonies were checked regularly to monitor their conditions and assess any threats to the birds. When a colony was discovered in an agricultural corn field, the landowner was contacted and CDFW worked with the NRCS to ensure the colonies were protected by providing financial compensation for harvest delays. A colony response partnership with NRCS, Audubon California, Western United Dairymen and California Farm Bureau ensured a rapid response to threatened colonies and effective communication with landowners.
Research on the Effects of Drought and Food Landscapes:
CDFW hired scientists from UC Davis and the National Audubon Society to evaluate the effects of precipitation and water availability on colony size, occupation, reproductive success and use of different habitats. types. This work will also evaluate the potential impacts of drought on food habitat availability at the landscape scale. Additionally, spatial modeling will be performed to characterize the foraging landscape around thriving colonies and changes in these landscapes over time. Ultimately, this work will be used to prioritize areas for conservation and restoration of breeding habitat.
Habitat Restoration:
The CDFW worked with the Lower Tule River Irrigation District and the U.S. Fish and Wildlife Service to restore high-quality spawning habitat in a groundwater recharge basin in Tulare County. This area has historically been home to large colonies of tri-colored blackbirds (up to 40,000 breeding adults), but the lack of a reliable water source has compromised wetland breeding habitat, and the area has remained uninhabited for many years . CDFW has funded the repair of a well that will provide reliable water to the site, and USFWS has agreed to provide local biologists to advise the irrigation district on best practices for managing tri-colored blackbird breeding habitat. The site is located a few kilometers from numerous other colony sites established on agricultural triticale fields and should therefore provide an alternative nesting site without conflict with local dairies.
Colony Detection, Monitoring, and Protection:
CDFW conducted an effort during the 2016 breeding season to locate and monitor all breeding colonies operating in agriculture. Cereals were produced. . Fields where they are vulnerable to crop failure. Contractors and staff from CDFW, Audubon California and other collaborators located colonies of tri-colored blackbirds on nine different farms in 2016. One of these colonies failed due to predation soon after establishment, but due to cooperative agreements with farmers. All remaining tri-colored blackbird colonies on agricultural fields were protected during the 2016 breeding season. Working with NRCS and other partners, eight farmers delayed their harvest, resulting in approximately 60,000 tri-colored blackbird nests being protected. Programs that compensate landowners for harvest delays have been around for many years, but 2016 was the first year that every colony found in an agricultural field was included in a colony protection program.
Habitat Restoration:
The well used to support the restoration of wetland spawning habitat in Tulare County is currently under repair (August 2016). The well will maintain water in a 40-acre wetland and will be jointly managed with CDFW and USFWS to improve the quality of the blackbird breeding site. The site is expected to support productive breeding habitat beginning in the 2017 breeding season.
Future Efforts
CDFW is working closely with the Tricolor Blackbird Working Group, including habitat restoration and research committees. Work completed through drought funding will inform ongoing efforts to implement the Tricolored Blackbird Conservation Plan, including restoring natural habitats that provide long-term benefits and increase resilience to current and future droughts. Opportunities for habitat protection and creation depend on continued investigation of the landscape conditions surrounding successful breeding colonies. Restored wetland habitat in Tulare County will continue to be monitored for the duration of the agreement with the irrigation district and USFWS (through 2027). Although not funded by drought-related funds, CDFW will help coordinate and implement the next triennial survey in 2017, which will report on the status of the population and indicate whether recently observed declines continue.
