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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Wetland fidelity of female Mallard Anas platyrhynchos and Gadwall Anas strepera during brood rearing
Auteurs :	R. G. Clark, Auteur ; S. W. Leach, Auteur ; K. W. Dufour, Auteur ; M. Gendron, Auteur
Type de document :	Article
Dans :	Wildfowl (55 2005)
Article en page(s) :	17-28
Langues:	Anglais
Résumé :	Occurrence of and factors affecting fidelity to brood-rearing areas have received little attention in ducks; thus, data from individually marked female Mallard Anas platyrhynchos and Gadwall Anas strepera collected over 5-7 years were used to investigate these patterns and processes. First, it was determined whether the 30-day tracking period used in most recent brood survival studies was sufficient for characterising wetland use. Radio-marked Mallard (n = 15) that were tracked consistently for 50 days had moved 93% of total distance travelled within 30 days whereas Gadwall (n = 8) had travelled > 99% of total distance moved in 40 days. Thus, a 30-day tracking period appeared adequate for both species. In several instances, marked ducklings of female parents that had been killed or had abandoned their brood were recaptured fully grown later in summer or when nesting in later years. Using recaptures of web-tagged ducklings from 69 Mallard and 49 Gadwall broods, an estimate was made of how often errors occurred in declaring total brood Loss in radio-marked broods. In most years, designation of complete brood Loss was about 5% higher than adjusted estimates and, overall, brood toss declined by 9% in Mallard and 13% in Gadwall after accounting for recaptures. In Mallard, 33% of female offspring (n = 15) and 50% of female parents (n = 12) reused at least one brood-rearing wetland in a later year, as did most female Gadwall offspring (75%, n = 4) and at[ three female Gadwall parents. Female Mallard offspring spent 2-26 days (mean 11 days) on their natal brood ponds and female parents spent 4-30 days (mean 15 days) there; ranges were 2-21 days for female Gadwall offspring and 2-7 days for female parents. Logistic regression analysis of wetland reuse revealed that female parents had greater fidelity than female offspring to previously used wetlands. Probability of reusing wetlands was unrelated to previous fledging success. Distances from previously used brood-rearing or natal wetlands to wetlands used >= 1 year later were much closer together than expected (when compared with distances and directional bearings to randomly selected, brood-rearing wetlands). Thus, females of both species tended to return to specific wetlands or brood-rearing areas they had used previously. In philopatric duck species, local populations of brood-rearing females could be well structured spatially according to family lineage in areas of stable wetland conditions.

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