Annual Reproductive Success of American Robins (Turdus migratorius) At the Northern Edge of Their Range

High arctic latitudes are characterized by short summers with continuous daylight, high seasonality, and low temperatures. In stable bird populations, mortality risks associated with the harsh climate and/or the long migration to reach the Arctic should be balanced by increased recruitment to the population through increased fecundity. We report on annual reproductive success of the American Robin (Turdus migratorius) nesting at its most northerly geographic limits in Ivvavik National Park, Yukon Territory, Canada during the 2010-2012 breeding seasons. Our objective was to determine whether fecundity was increased relative to similar populations breeding at more southerly latitudes. We also examined interannual variation in breeding parameters, which we predicted would vary because of interannual variation in local weather conditions. Clutch completion date, clutch size, and fledglings per nest varied significantly among years. No re-nests or double-brooding were documented. There was a significant decrease in incubation period and increase in nest success and clutch size with increasing latitude. Nests in Ivvavik National Park contained more fledglings per successful nest than nests farther south, and the nestling period (11 days) was the shortest recorded for this species. The lack of double-brooding appears to be at least partially compensated by higher fecundity during the single breeding event, at this northerly location.