Timing of breeding and reproductive success in a subarctic population of yellow warblers (Dendroica petechia)

Abstract

Detailed knowledge of reproductive rates is necessary for understanding population dynamics, but this information is lacking for many populations of migratory songbirds. I examined breeding chronology and reproductive success of Yellow Warblers (Dendroica petechia) breeding in east central Alaska in 1997-2000. Yellow Warblers nested in both spruce forest and willow shrub habitats, but breeding density and nest success were greater in shrub habitat. Annual productivity was influenced by the number of breeding attempts per female, clutch size, success of individual eggs or nestlings, and nest success. Mean clutch size was larger than in lower latitude populations and decreased seasonally. The abbreviated breeding season limited opportunities for replacing lost clutches or broods, but enough females replaced failed nests to increase annual productivity by 0.5 fledglings per female, on average. Nest predation was likely the primary cause of nest failures and was greater on the edge between willow shrub and spruce forest than within the interior of those habitats. Timing of breeding was consistent in three years of the study, but early laying in 1998, which coincided with warmer air temperatures, effectively extended the breeding season. Extremely low nest success lowered annual productivity in 1998, despite the extended breeding season.