Nesting Ecology of the Rusty Blackbird in Alaska and Canada

Abstract

Abstract. We examined the nesting ecology of the Rusty Blackbird (Euphagus carolinus) from 162 nests monitored for nest survival in Alaska and 252 incidental records from Alaska and Canada to identify important habitats for nesting and to test whether low rates of nest success are contributing to populations declines in Alaska. In coastal Alaska and throughout Canada, nests were primarily in conifers (85% of 212 nests). All conifer nests in Alaska and 80% of those in Canada were placed in spruce (Picea spp.), primarily black spruce (P. mariana). In Alaska use of small spruces (<8 cm dbh) was selective and resulted in high reproductive success—nest survival increased with black spruce density, and success of nests in spruce (79%) was higher than that of nests in deciduous vegetation (52%). Survival of nests in taller spruce declined, possibly from predation by red squirrels (Tamiasciurus hudsonicus). Rusty Blackbirds nested near water in interior ( = 8 m) and south-central Alaska ( = 30 m), and small spruces near water appear to be important over much of the species' range. In interior Alaska, however, most nests were in willows (78%), which dominated the vegetation near water. Nest success in Alaska averaged 56%, similar to rates over the same period in New England but higher than those of other North American blackbirds (30–39%). Studies are needed to verify whether nest survival is also high in Canada and to investigate where and why deficits in survival of adults or juveniles may be limiting population growth.