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Tricolored blackbird (Agelaius tricolor) is a colonial breeder, largely restricted to grasslands, wetlands, and agricultural areas of California, USA. Tricolored blackbird abundance declined considerably during the twentieth century. Recent trends have been less clear, however, hindering efforts to evaluate the conservation needs of the species. We assessed trends in tricolored blackbird colony size using 2008, 2011, 2014, and 2017 Triennial Tricolored Blackbird Statewide Survey, a community‐science effort involving hundreds of volunteer observers. After accounting for variation in observer characteristics and survey effort, we found a clear, statistically significant decrease in average colony size of approximately 5% per year, which translated to a decrease in average colony size of approximately 40% between 2008 and 2017. This decrease in colony size matches the overall decline in abundance reported in another recent study and reinforces the conclusion that tricolored blackbird is in need of protection and recovery efforts. © 2019 The Authors. The Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society. We assessed trends in tricolored blackbird colony size using community science surveys, explicitly modeling variation in observer identity and effort, California, USA, 2008–2017. We documented a 5% annual decline in colony size, which translated to a 40% decline in colony size over the past decade. [ABSTRACT FROM AUTHOR]

Since the early 1990s when much of the population of the Tricolored Blackbird (Agelaius tricolor) began nesting in fields of triticale grown for dairy silage in the San Joaquin Valley, many colonies have been destroyed inadvertently during harvest. After previous inconsistent efforts, in 2015 a Regional Conservation Partnership Program brought the dairy industry, Natural Resource Conservation Service, Audubon California, California Department of Fish and Wildlife, and other partners together in an effort to stem the losses. The program located colonies and compensated farmers for crop value lost when the harvest was delayed until after the blackbirds fledged and encouraged creation of alternative nesting habitat to attract nesting birds away from agricultural fields. Before 2015, data on the numbers of colonies in silage fields, and on the blackbirds' productivity conserved and lost, are complete only for 2005-2009, when only 43% of colonies encompassing 60% of the monitored nestings avoided destruction. From 2015 to 2022, 93% of colonies representing 96% of nesting attempts were conserved, and the number of birds nesting in silage increased by as much as 100,000. The program's success resulted from the adequacy of federal funding, protection provided by the species' listing as endangered by the state of California, and effective communications and cooperation among the partners and within the dairy industry. Protection of colonies in silage fields since 2015 likely contributed to the substantial increase in the numbers of birds nesting in this habitat and perhaps to an increase in California's Tricolored Blackbird population as a whole. Continued effort is needed to achieve the species' recovery. [ABSTRACT FROM AUTHOR]