RESUMEN
For organisms in seasonal environments, individuals that breed earlier in the season regularly attain higher fitness than their late-breeding counterparts. Two primary hypotheses have been proposed to explain these patterns: The quality hypothesis contends that early breeders are of better phenotypic quality or breed on higher quality territories, whereas the date hypothesis predicts that seasonally declining reproductive success is a response to a seasonal deterioration in environmental quality. In birds, food availability is thought to drive deteriorating environmental conditions, but few experimental studies have demonstrated its importance while also controlling for parental quality. We tested predictions of the date hypothesis in tree swallows (Tachycineta bicolor) over two breeding seasons and in two locations within their breeding range in Canada. Nests were paired by clutch initiation date to control for parental quality, and we delayed the hatching date of one nest within each pair. Subsequently, brood sizes were manipulated to mimic changes in per capita food abundance, and we examined the effects of manipulations, as well as indices of environmental and parental quality, on nestling quality, fledging success, and return rates. Reduced reproductive success of late-breeding individuals was causally related to a seasonal decline in environmental quality. Declining insect biomass and enlarged brood sizes resulted in nestlings that were lighter, in poorer body condition, structurally smaller, had shorter and slower growing flight feathers and were less likely to survive to fledge. Our results provide evidence for the importance of food resources in mediating seasonal declines in offspring quality and survival.
RESUMEN
Adults of the flea, Ceratophyllus vagabundus vagabundus , were present in the hundreds in nests of Ross's (Chen rossii) and lesser snow (Chen caerulescens caerulescens) geese in the Arctic goose colony at Karrak Lake, Nunavut, Canada. Ceratophyllus v. vagabundus had not been previously recorded in association with Ross's or snow geese. Large numbers of C. v. vagabundus adults and larvae were collected and a description of the larva is provided for the first time. On the basis of external characters, larvae were indistinguishable from those of a number of other Ceratophyllus spp. previously described from North America, i.e., Ceratophyllus idius, Ceratophyllus niger, and Ceratophyllus lari.