Habitat Quality, Population Density and Habitat-specific Productivity of Red-winged Blackbirds (Agelaius phoeniceus) in Boulder County, Colorado

Abstract

I monitored 382 red-winged blackbird (Agelaius phoeniceus) nests in natural (wetlands and tallgrass prairie) and human-disturbed (hayfields, roadside ditches) habitats in the vicinity of Boulder, Colorado during 1996 and 1997. I counted blackbirds in a total of 6216 ha and quantified habitat composition to determine both within-habitat population density and regional habitat availability. Population density mirrored habitat-specific productivity of red-winged blackbirds in habitats that had predictable sources of water (wetlands, roadside ditches). However, population density and habitat-specific productivity were decoupled in habitats that were unpredictable in the amount of water present during territory establishment (tallgrass prairie and hayfields, which were flood irrigated). Regional habitat productivity was estimated using data on habitat-specific productivity, habitat-specific population density and regional habitat availability. Red-winged blackbirds breeding in wetlands in the absence of yellow-headed blackbirds (Xanthocephalus xanthocephalus) contributed the most young to the regional population, whereas birds breeding in human-disturbed habitats (hayfields and roadside ditches) contributed relatively few young to the regional population. Due to the scarcity of high quality patches in the landscape (e.g., tallgrass prairie), the highest quality habitats did not always contribute the most young to the regional population.