Possible causes and consequences of philopatry and breeding dispersal in red-backed shrikes <Emphasis Type="BoldItalic">Lanius collurio</Emphasis> |
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Authors: | Gilberto Pasinelli Mathis Müller Michael Schaub Lukas Jenni |
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Institution: | (1) Institute of Zoology, Ecology Group, University of Zurich, CH-8057 Zurich, Switzerland;(2) Swiss Ornithological Institute, CH-6204 Sempach, Switzerland;(3) Zoological Institute, Division Conservation Biology, University of Bern, CH-3012 Bern, Switzerland |
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Abstract: | Studies of animal breeding dispersal have often focused on possible causes, whereas its adaptive significance has received
less attention. Using an information-theoretic approach, we assessed predictions of four hypotheses relating to causes and
consequences of breeding dispersal in a migratory passerine, the red-backed shrike Lanius collurio. As predicted by the reproductive performance hypothesis, probability of breeding dispersal in females (though not in males)
decreased with increasing annual average number of fledglings produced in the past year, but there was no association with
conspecific reproductive performance in either sex. The site choice hypothesis, stating that individuals disperse to improve
breeding site quality, received support in males only, as dispersal probability was positively associated to a measure indicating
low territory quality. The social constraints hypothesis, referring to dispersal in relation to intraspecific interactions,
received little support in either sex. The predation risk hypothesis was hardly supported either. Consequences of dispersal
were marginal in both sexes because neither fledgling production in females, nor territory quality in males improved after
dispersal. In addition, males settled on territories closer to the forest edge than those occupied predispersal, which is
opposite to the prediction of the predation risk hypothesis. We conclude that own reproductive success was the major factor
determining dispersal behavior in females, whereas territory quality and possibly predation risk were most important in males.
Overall, breeding dispersal appeared not to be adaptive in this dense population inhabiting an optimal habitat. |
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Keywords: | AIC Reproductive performance Site choice Social constraints Predation risk |
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