Recherche

Bitton, Pierre-Paul; Dawson, Russell D. — 2016-10-14 Reproductive success and nestling performance are related to the age of parents across several vertebrate taxa. However, because breeding experience and prenatal maternal investment in reproduction often covary, the source of these age-related differences can be difficult to determine. In this study, we evaluated the influence of prenatal maternal effects and postnatal breeding experience on the performance of nestling tree swallows Tachycineta bicolor by conducting a carefully controlled partial cross-fostering experiment. We swapped half-broods of nestlings between the nest of a young first-time breeding female and the nest of a female known to have previously raised and fledged young. Our manipulation did not influence the within-brood nestling hierarchies, and controlled for the effects of egg laying order. We found that nestlings of older females were heavier just prior to fledging regardless of the breeding experience of the attending female. In addition, fledglings raised by experienced females grew their flight feathers faster, and had greater probability of fledging. Our study demonstrates that prenatal investment in reproduction by older females can have long-term consequences on nestling mass, and suggests limited potential for compensatory mass gains prior to fledging. Because our analyses controlled for feeding rates, our results also suggest that foraging quantity and quality are not the only benefits nestlings gain by being raised by an experienced female.

Fairhurst, Graham D.; Berzins, Lisha L.; Bradley, David W.; Laughlin, Andrew J.; Romano, Andrea; Romano, Maria; Scandolara, Chiara; Ambrosini, Roberto; Dawson, Russell D.; Dunn, Peter O.; Hobson, Keith A.; Liechti, Felix; Marchant, Tracy A.; Norris, D. Ryan; Rubolini, Diego; Saino, Nicola; Taylor, Caz M.; Whittingham, Linda A.; Clark, Robert G. — 2015-03-26 Despite benefits of using light-sensitive geolocators to track animal movements and describe patterns of migratory connectivity, concerns have been raised about negative effects of these devices, particularly in small species of aerial insectivore. Geolocators may act as handicaps that increase energetic expenditure, which could explain reported effects of geolocators on survival. We tested this ‘Energetic Expenditure Hypothesis’ in 12 populations of tree swallows (Tachycineta bicolor) and barn swallows (Hirundo rustica) from North America and Europe, using measurements of corticosterone from feathers (CORTf) grown after deployment of geolocators as a measure of physiology relevant to energetics. Contrary to predictions, neither among- (both species) nor within-individual (tree swallows only) levels of CORTf differed with respect to instrumentation. Thus, to the extent that CORTf reflects energetic expenditure, geolocators apparently were not a strong handicap for birds that returned post-deployment. While this physiological evidence suggests that information about migration obtained from returning geolocator-equipped swallows is unbiased with regard to levels of stress, we cannot discount the possibility that corticosterone played a role in reported effects of geolocators on survival in birds, and suggest that future studies relate corticosterone to antecedent factors, such as reproductive history, and to downstream fitness costs. https://creativecommons.org/publicdomain/zero/1.0/

Gow, Elizabeth A.; Burke, Lauren; Winkler, David W.; Knight, Samantha M.; Clark, Robert G.; Bélisle, Marc; Berzins, Lisha L.; Blake, Tricia; Bridge, Eli S.; Dawson, Russell D.; Dunn, Peter O.; Garant, Dany; Holroyd, Geoff; Horn, Andrew G.; Hussell, David J.T.; Lansdorp, Olga; Laughlin, Andrew J.; Leonard, Marty L.; Pelletier, Fanie; Shutler, Dave; Siefferman, Lynn; Taylor, Caz M.; Trefry, Helen; Vleck, Carol M.; Vleck, David; Whittingham, Linda A.; Norris, D. Ryan — 2018-12-13 Latitudinal differences in timing of breeding are well documented but how such differences carry over to influence timing of events in the annual cycle of migratory birds is not well understood. We examined geographic variation in timing of events throughout the year using light-level geolocator tracking data from 133 migratory tree swallows (Tachycineta bicolor) originating from 12 North American breeding populations. A swallow’s breeding latitude influenced timing of breeding, which then carried over to affect breeding ground departure. This resulted in subsequent effects on the arrival and departure schedules at fall stopover locations and timing of arrival at non-breeding locations. This “domino effect” between timing events was no longer apparent by the time individuals departed for spring migration. Our range-wide analysis demonstrates the lasting impact breeding latitude can have on migration schedules but also highlights how such timing relationships can reset when individuals reside at non-breeding sites for extended periods of time.