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Résumé :
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Studies of the dynamics of carcass components are critical to understanding survival and reproduction in waterfowl. Here, we examined the influence of sex, age, and season on the carcass composition of American Wigeon (Anas americana) in the Southern High Plains (SHP) of Texas during the migration and wintering periods. Wigeon (N = 621) were collected from late fall through early spring, and carcass components (lipid, protein, and mineral) were estimated for each bird. Overall, carcass mass and lipids increased from autumn to early or midwinter and declined thereafter. However, over-winter changes in carcass reserves differed among sex and age groups. Wigeon of different sex and age groups maintained lipid and protein reserves to different degrees and used those reserves through the winter at different rates. The lack of premigratory fattening suggests that wigeon in the SHP must obtain most of the resources necessary for reproduction en route to breeding grounds, and highlights the importance of suitable stopover locations on their migratory routes. Changes in mean structural size of wigeon sampled during the nonbreeding season, in conjunction with genetic data, suggest that the wintering population in the SHP was composed of birds from several breeding populations. Our research will aid migratory bird biologists in determining how wigeon that differ in sex and age meet their over-winter resource needs, and in evaluating the responses of wigeon to habitat conservation and management efforts.
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