title: Assessing costs of carrying geolocators using feather corticosterone in two species of aerial insectivore.
abstract: 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.
authors.affiliation: Department of Biology , University of Saskatchewan , 112 Science Place, Saskatoon, Saskatchewan, Canada S7N 5E2 ; Environment Canada, 115 Perimeter Road, Saskatoon , Saskatchewan, Canada S7N 0X4.
authors.forename: Graham D
authors.identifier: 0000-0001-8731-1298
authors.initials: GD
authors.lastname: Fairhurst
authors.affiliation: Ecosystem Science and Management , University of Northern British Columbia, 3333 University Way, Prince George , British Columbia, Canada V2N 4Z9.
authors.forename: Lisha L
authors.initials: LL
authors.lastname: Berzins
authors.affiliation: Department of Integrative Biology , University of Guelph, 50 Stone Road East, Guelph , Ontario, Canada N1G 1E4 ; Bird Studies Canada, 115 Front Street, Port Rowan , Ontario, Canada N0E 1M0.
authors.forename: David W
authors.initials: DW
authors.lastname: Bradley
authors.affiliation: Department of Ecology and Evolutionary Biology , Tulane University , New Orleans, LA 70118, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Laughlin
authors.affiliation: Department of Biosciences , University of Milan , via Celoria 26, Milan 20133, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Romano
authors.affiliation: Department of Biosciences , University of Milan , via Celoria 26, Milan 20133, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Romano
authors.affiliation: Department of Biosciences , University of Milan , via Celoria 26, Milan 20133, Italy ; Swiss Ornithological Institute , Seerose 1, Sempach 6204, Switzerland.
authors.forename: Chiara
authors.initials: C
authors.lastname: Scandolara
authors.affiliation: Department of Biotechnology and Biosciences , University of Milano Bicocca , Piazza della Scienza 2, Milan 20126, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Ambrosini
authors.affiliation: Ecosystem Science and Management , University of Northern British Columbia, 3333 University Way, Prince George , British Columbia, Canada V2N 4Z9.
authors.forename: Russell D
authors.initials: RD
authors.lastname: Dawson
authors.affiliation: Department of Biological Sciences , University of Wisconsin-Milwaukee , 3209 North Maryland Avenue, Milwaukee, WI 53201-0413, USA.
authors.forename: Peter O
authors.initials: PO
authors.lastname: Dunn
authors.affiliation: Environment Canada , 11 Innovation Boulevard, Saskatoon , Saskatchewan, Canada S7N 3H5.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Hobson
authors.affiliation: Swiss Ornithological Institute , Seerose 1, Sempach 6204, Switzerland.
authors.forename: Felix
authors.initials: F
authors.lastname: Liechti
authors.affiliation: Department of Biology , University of Saskatchewan , 112 Science Place, Saskatoon, Saskatchewan, Canada S7N 5E2.
authors.forename: Tracy A
authors.initials: TA
authors.lastname: Marchant
authors.affiliation: Department of Integrative Biology , University of Guelph, 50 Stone Road East, Guelph , Ontario, Canada N1G 1E4.
authors.forename: D Ryan
authors.initials: DR
authors.lastname: Norris
authors.affiliation: Department of Biosciences , University of Milan , via Celoria 26, Milan 20133, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Rubolini
authors.affiliation: Department of Biosciences , University of Milan , via Celoria 26, Milan 20133, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Saino
authors.affiliation: Department of Ecology and Evolutionary Biology , Tulane University , New Orleans, LA 70118, USA.
authors.forename: Caz M
authors.initials: CM
authors.lastname: Taylor
authors.affiliation: Department of Biological Sciences , University of Wisconsin-Milwaukee , 3209 North Maryland Avenue, Milwaukee, WI 53201-0413, USA.
authors.forename: Linda A
authors.initials: LA
authors.lastname: Whittingham
authors.affiliation: Department of Biology , University of Saskatchewan , 112 Science Place, Saskatoon, Saskatchewan, Canada S7N 5E2 ; Environment Canada, 115 Perimeter Road, Saskatoon , Saskatchewan, Canada S7N 0X4.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Clark
keywords: Energetic Expenditure Hypothesis; feather corticosterone; hormone biomarkers; light-level geolocators; migration physiology; swallows