Restored Fire and Grazing Regimes Influence Nest Selection and Survival in Brewer's Blackbirds Euphagus cyanocephalus

Abstract

Abstract. Grassland fire suppression causes numerous ecological changes including increases in woody vegetation, reduced biodiversity, and population declines of grassland species. Elimination of vegetation structure created and maintained by fire is a major driver of these changes. In this study, we documented a seldom-described nesting preference in Brewer's Blackbirds Euphagus cyanocephalus through the discovery of 56 nests in recently burned (0 and 1 years-since-fire) mixed-grass prairie. After locating nests via systematic rope dragging, we monitored them to characterize fates and then measured vegetation characteristics at and near nests to determine how vegetation structure influences nest survival. Most Brewer's Blackbird nests were located in patches burned within 1.5 years of the nesting attempt, though such patches made up 21% of the landscape. Nests were located on the ground and consisted of fine grasses lined with animal hair. Site selection analysis showed that Brewer's Blackbirds were 38 and 34 times more likely to nest in 0 and 1 year-since-fire patches than unburned patches, respectively. Nest survival analysis indicated a daily survival rate of 0.96 (0.32 overall survival). Lower survival rates were associated with higher bare ground and litter cover at the microsite (5 m from nest) and nest site (at nest), respectively. These results demonstrate that Brewer's Blackbirds exploit fire-associated vegetation structure in tree-limited landscapes. This research suggests that restored grassland disturbance regimes extend broad benefits to non-obligate taxa, as well as reveals previously repressed fire-associated behaviors of wildlife.