Agelaius tricolor

A. phoeniceus a sister taxon (AOU 1998).

This species largely lives within the Central Valley of California with peripheral populations as far north as Washington and as far south as Baja California Norte. The population has suffered severe declines of at least 80% compared to historical estimates due to habitat loss. Due to the loss of wetlands, the species is largely relegated to living in agricultural settings. It is threatened by further habitat loss and by agricultural practices that are incompatible with nesting and foraging. Since 2014, the population has increased by 50%. However, it still remains a small fraction of historical population size.

The breeding range extends from central southern Oregon south through interior California, and along the coast from central California south to localized areas in northwestern Baja California (Beedy et al. 2023).

During the nonbreeding period the range contracts somewhat as the species withdraws from several areas around the margins of the breeding range (Beedy et al. 2023). Idaho records from 2023 appear to only represent the nonbreeding range (Olsoy and Sorensen 2024).

The 2022 statewide survey in California found blackbirds breeding in 158 locations (Colibri Ecological Consulting 2022).

The species has undergone a long-term population decline, primarily due to losses and fragmentation of breeding and foraging habitats caused by urban and agricultural land conversions, and water diversions (Tricolored Blackbird Working Group 2007). Most of California's formerly extensive freshwater wetlands have been lost, and the remaining ones often are small isolated patches that support high densities of natural predators (e.g., coyote, raccoon, black-crowned night-heron, common raven; great-tailed grackle in southern California), which sometimes may cause significant reductions in blackbird reproductive success through predation or disturbance (Tricolored Blackbird Working Group 2007). Formerly productive foraging habitats (especially those within 5-6 km of breeding colony sites) have been lost to perennial, woody crops (primarily almonds and grapes) and to urbanization (Tricolored Blackbird Working Group 2007). In addition, untimely harvesting of silage grains in locations where colonies have settled causes complete breeding failure of many thousands of birds for at least one breeding attempt (Cook and Toft 2005, Beedy 2008, Castañeda et al. 2023). This threat has been reduced through programs working with landowners to delay silage harvest and reimburse losses caused by delays (Castañeda et al. 2023).

Inappropriate water management sometimes causes nesting failures if managed water levels are too shallow (not deep enough to deter raccoon and other predators) or too deep (flooding nests, such as has occurred at Lake Isabella) (Tricolored Blackbird Working Group 2007). Low water levels generally defined unoccupied sites in California (Wilsey et al. 2019).

Pesticides do not appear to be directly impacting birds, though the population has almost certainly seen drastic reductions in insect prey availability (USFWS 2006, Graves et al. 2023).