Effectiveness of Public–Private Efforts to Conserve Tricolored Blackbird Colonies on Agricultural Lands in the San Joaquin Valley, California

Abstract

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.