Low survival after release into the wild: assessing “the burden of captivity” on Mallard physiology and behaviour |
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Authors: | Jocelyn Champagnon Matthieu Guillemain Johan Elmberg Grégoire Massez Francois Cavallo Michel Gauthier-Clerc |
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Institution: | (1) Office National de la Faune Sauvage, CNERA Avifaune Migratrice, Tour du Valat, Le Sambuc, 13200 Arles, France;(2) Centre de Recherche de la Tour du Valat, Le Sambuc, 13200 Arles, France;(3) Centre d’Ecologie Fonctionnelle et Evolutive UMR 5175-CNRS, 1919 Route de Mende, 34293 Montpellier Cedex 5, France;(4) Aquatic Biology and Chemistry, Kristianstad University, 291 88 Kristianstad, Sweden;(5) Les Marais du Vigueirat, Mas Thibert, 13200 Arles, France |
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Abstract: | Captive-reared animals used in reinforcement programs are generally less likely to survive than wild conspecifics. Digestion
efficiency and naive behaviour are two likely reasons for this pattern. The Mallard is a species with high adaptability to
its environment and in which massive reinforcement programs are carried out. We studied physiological and behavioural factors
potentially affecting body condition and survival of captive-reared Mallards after being released. Digestive system morphology
and an index of body condition were compared among three groups: captive-reared birds remaining in a farm (control), captive-reared
birds released into the wild as juveniles (released) and wild-born birds (wild). We also compared behaviour and diet of released
vs. wild Mallards. Finally, we conducted a 1-year survival analysis of captive-reared birds after release in a hunting-free
area. Gizzard weight was lower in control Mallards, but the size of other organs did not differ between controls and wild
birds. The difference in gizzard weight between released and wild birds disappeared after some time in the wild. Diet analyses
suggest that released Mallards show a greater preference than wild for anthropogenic food (waste grain, bait). Despite similar
time-budgets, released Mallards never attained the body condition of wild birds. As a consequence, survival probability in
released Mallards was low, especially when food provisioning was stopped and during harsh winter periods. We argue that the
low survival of released Mallards likely has a physiological rather than a behavioural (foraging) origin. In any case, extremely
few released birds live long enough to potentially enter the breeding population, even without hunting. In the context of
massive releases presently carried out for hunting purposes, our study indicates a low likelihood for genetic introgression
by captive-reared birds into the wild population. |
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