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      Assessing costs of carrying geolocators using feather corticosterone in two species of aerial insectivore

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          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 (CORT f) 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 CORT f differed with respect to instrumentation. Thus, to the extent that CORT f 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.

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          Most cited references19

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          Carry-over effects as drivers of fitness differences in animals.

          1. Carry-over effects occur when processes in one season influence the success of an individual in the following season. This phenomenon has the potential to explain a large amount of variation in individual fitness, but so far has only been described in a limited number of species. This is largely due to difficulties associated with tracking individuals between periods of the annual cycle, but also because of a lack of research specifically designed to examine hypotheses related to carry-over effects. 2. We review the known mechanisms that drive carry-over effects, most notably macronutrient supply, and highlight the types of life histories and ecological situations where we would expect them to most often occur. We also identify a number of other potential mechanisms that require investigation, including micronutrients such as antioxidants. 3. We propose a series of experiments designed to estimate the relative contributions of extrinsic and intrinsic quality effects in the pre-breeding season, which in turn will allow an accurate estimation of the magnitude of carry-over effects. To date this has proven immensely difficult, and we hope that the experimental frameworks described here will stimulate new avenues of research vital to advancing our understanding of how carry-over effects can shape animal life histories. 4. We also explore the potential of state-dependent modelling as a tool for investigating carry-over effects, most notably for its ability to calculate optimal rates of acquisition of a multitude of resources over the course of the annual cycle, and also because it allows us to vary the strength of density-dependent relationships which can alter the magnitude of carry-over effects in either a synergistic or agonistic fashion. 5. In conclusion carry-over effects are likely to be far more widespread than currently indicated, and they are likely to be driven by a multitude of factors including both macro- and micronutrients. For this reason they could feasibly be responsible for a large amount of the observed variation in performance among individuals, and consequently warrant a wealth of new research designed specifically to decompose components of variation in fitness attributes related to processes across and within seasons. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.
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            Biotelemetry: a mechanistic approach to ecology.

            Remote measurement of the physiology, behaviour and energetic status of free-living animals is made possible by a variety of techniques that we refer to collectively as 'biotelemetry'. This set of tools ranges from transmitters that send their signals to receivers up to a few kilometers away to those that send data to orbiting satellites and, more frequently, to devices that log data. They enable researchers to document, for long uninterrupted periods, how undisturbed organisms interact with each other and their environment in real time. In spite of advances enabling the monitoring of many physiological and behavioural variables across a range of taxa of various sizes, these devices have yet to be embraced widely by the ecological community. Our review suggests that this technology has immense potential for research in basic and applied animal ecology. Efforts to incorporate biotelemetry into broader ecological research programs should yield novel information that has been challenging to collect historically from free-ranging animals in their natural environments. Examples of research that would benefit from biotelemetry include the assessment of animal responses to different anthropogenic perturbations and the development of life-time energy budgets.
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              Tracking long-distance songbird migration by using geolocators.

              We mapped migration routes of migratory songbirds to the Neotropics by using light-level geolocators mounted on breeding purple martins (Progne subis) and wood thrushes (Hylocichla mustelina). Wood thrushes from the same breeding population occupied winter territories within a narrow east-west band in Central America, suggesting high connectivity of breeding and wintering populations. Pace of spring migration was rapid (233 to 577 kilometers/day) except for one individual (159 kilometers/day) who took an overland route instead of crossing the Gulf of Mexico. Identifying songbird wintering areas and migration routes is critical for predicting demographic consequences of habitat loss and climate change in tropical regions.
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                Author and article information

                Journal
                R Soc Open Sci
                R Soc Open Sci
                RSOS
                royopensci
                Royal Society Open Science
                The Royal Society Publishing
                2054-5703
                May 2015
                6 May 2015
                6 May 2015
                : 2
                : 5
                : 150004
                Affiliations
                [1 ]Department of Biology, University of Saskatchewan , 112 Science Place, Saskatoon, Saskatchewan, Canada S7N 5E2
                [2 ]Environment Canada, 115 Perimeter Road, Saskatoon , Saskatchewan, Canada S7N 0X4
                [3 ]Ecosystem Science and Management, University of Northern British Columbia, 3333 University Way, Prince George , British Columbia, Canada V2N 4Z9
                [4 ]Department of Integrative Biology, University of Guelph, 50 Stone Road East, Guelph , Ontario, Canada N1G 1E4
                [5 ]Bird Studies Canada, 115 Front Street, Port Rowan , Ontario, Canada N0E 1M0
                [6 ]Department of Ecology and Evolutionary Biology, Tulane University , New Orleans, LA 70118, USA
                [7 ]Department of Biosciences, University of Milan , via Celoria 26, Milan 20133, Italy
                [8 ]Swiss Ornithological Institute, Seerose 1, Sempach 6204, Switzerland
                [9 ]Department of Biotechnology and Biosciences, University of Milano Bicocca , Piazza della Scienza 2, Milan 20126, Italy
                [10 ]Department of Biological Sciences, University of Wisconsin—Milwaukee , 3209 North Maryland Avenue, Milwaukee, WI 53201-0413, USA
                [11 ]Environment Canada, 11 Innovation Boulevard, Saskatoon , Saskatchewan, Canada S7N 3H5
                Author notes
                Author for correspondence: Graham D. Fairhurst e-mail: graham.fairhurst@ 123456usask.ca
                Author information
                http://orcid.org/0000-0001-8731-1298
                Article
                rsos150004
                10.1098/rsos.150004
                4453251
                26064659
                94ae5e44-ed03-4428-b52b-3d8443005ac8

                © 2015 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

                History
                : 6 January 2015
                : 7 April 2015
                Categories
                1001
                202
                60
                14
                Biology (Whole Organism)
                Research Article
                Custom metadata
                May, 2015

                energetic expenditure hypothesis,feather corticosterone,hormone biomarkers,light-level geolocators,migration physiology,swallows

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