Tricolored Blackbird Conservation Status and Opportunities in the Sierra Nevada Foothills of California

Abstract

In 2018, we estimated the number, sizes, and success of Tricolored Blackbird (Agelaius tricolor) breeding colonies in the central portion of the Sierra Nevada foothills, California, as part of an ongoing regional evaluation of the species’ status. We also evaluated effects of precipitation on the breeding population size and documented nesting substrates, colony success and land use conflicts. Over 58,000 tricolors bred at 24 colony sites in the foothill region in 2018, a year with above average rainfall. Multi-year analysis did not show a relationship between rainfall and breeding population size. Colony success (i.e., those fledging at least some young) was high, at 96%. Nesting occurred primarily in patches of non-native Himalayan blackberry (Rubus armeniacus; 77% of colony sites). Several colony sites with past histories of regular nesting use were not used after construction activities occurred nearby.