|Abstract or Summary
- The Rusty Blackbird (Euphagus carolinus) has suffered significant population declines across its entire geographic range and the mechanisms associated with this decline are poorly understood. Although much of the Rusty Blackbird breeding habitat in Alaska has remained relatively unaltered by anthropogenic activities, this species continues to decline by an estimated 5% annually. As part of a collaborative effort to obtain data on the reproductive ecology, breeding success, and habitat requirements of this species throughout their range, a total of 42 nests were found and monitored for two consecutive breeding seasons (2009 – 2010) on the Copper River Delta in south-central Alaska. Nests were monitored every 2-4 days to calculate nest success, survival rates, clutch initiation date, clutch size, egg viability, and fledging rates. In 2010, chick provisioning rates, chick diet, and aquatic invertebrate availability in Rusty Blackbird foraging habitats were also investigated. Mean clutch size ranged from 5 to 7 eggs both years (2009 = 5.41 ± 0.15, 2010 = 5.67 ± 0.13). Daily nest survival rate averaged over both seasons was high, at 0.9913 ± 0.0043 (95% CI 0.9772-0.9967) and most eggs were viable (N = 31 nests), with 0.8922 ± 0.0275 of eggs over both seasons hatching. Approximately 85% of clutches were initiated within a two week period for both years of the study. Clutch-initiation date (CID) was significantly different between years (p-value < 0.0001), with mean CID of 10 May (x̅ = 10.476 ± 0.95) in 2010 and May 18 (x̅ = 18.421 ± 1.13) in 2009. The mean provisioning rate was 0.84 (± 0.06; 95% CI: 0.72 to 0.95) invertebrate food items per chick per hour. Large odonate nymphs, specifically dragonflies, made up the bulk (97.2%) of the observed food items provisioned to chicks. Weekly pond sampling revealed four taxonomic groups of invertebrates that were of the size observed provisioned to chicks (Coleoptera, Hirudinea, Zygoptera, Anisoptera) and Anisoptera were among the rarest collected (16.2%) of this size. Although the least common large invertebrate collected, Anisoptera nymphs were present in all weekly samples. The week with the most abundant Anisoptera collection coincided with the week of peak hatching during 2010 of the study. Thus, availability of dragonfly nymphs appear to be important to Rusty Blackbird reproductive success on the Copper River Delta and may have contributed to the high nest success observed in this study.