International audienceDespite a long historical record of radio-tracking analyses, basic home-range information is still lacking for most common waterfowl species, especially during the winter. We investigated how dabbling duck home ranges and daily foraging movements are influenced by extrinsic (site, temperature, date) and intrinsic factors (species, sex, age). We radio-tagged and monitored 125 individuals of three duck species (mallard Anas platyrhynchos, Eurasian teal A. crecca crecca and northern pintail A. acuta) in three French wetlands over four winters. Home-range sizes for a given species varied greatly among our study sites. Moreover, species differed according to home-range structure and distance traveled to reach their foraging grounds (teal had a more patchy home range and traveled farther distances than mallards). Foraging distances increased with temperature and time (over the winter season), but this effect differed among species, suggesting that they behave differently in response to food depletion and/or cold weather. The commuting behavior (i.e., the decision to leave the roost at night for foraging) differed among species and season. Teals were more risk-prone because they were more likely to leave the roost at night. In our study, ducks foraged at distances of 1–2 km from roosts, whereas distances of 2–48 km have been recorded in North America. We suggest that food supply, hunting pressure or population density may account for these inter-continental differences
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Conspecific nest parasitism (CNP) is widespread among birds and is particularly common in colonial species. Nevertheless, this reproductive tactic is remarkably little described in terns. In this study we use egg morphology as indirect evidence of CNP in the whiskered tern (Chlidonias hybrida) in 17 colonies from two French populations. We study CNP with respect to the duration of egg laying (i.e. clutch size), and also present some behavioural aspects that could facilitate CNP. From the inspection of 121 two-egg, 279 three-egg and 11 more egg-clutches, we detected a minimum %CNP of 9.2% for the two study populations, combined with large differences between the two populations (4.0% vs. 14.5% in three-egg clutches) and between colonies (0 up to 30%). %CNP was significantly higher in three-egg (9.0%) than in two-egg clutches (1.7%), suggesting that duration of egg laying is a determining factor of parasitism. The rather high %CNP detected in this species might be facilitated by (1) the observed long unattendance of nest by any of the pair members, mainly during the pre-incubation period, and (2) high synchrony in laying dates within colonies. A possible link between nest density and CNP rate was suggested. Finally, we encourage new investigations of CNP in other tern species.
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