Emigration rates and population turnover of teal Anas crecca in two major wetlands of western Europe
2011
Caizergues, Alain | Guillemain, Matthieu | Arzel, Céline | Devineau, Olivier | Leray, Gilles | Pilvin, Daniel | Lepley, Michel | Massez, Grégoire | Schricke, Vincent
During the winter of 2003/04, we studied emigration rates of teal Anas crecca in two major wetlands: the Camargue (southern France) and the Loire estuary (western France). We derived local survival probabilities as a step in ultimately estimating emigration rates from individual mark‐resighting (visual recaptures) history of birds fitted with nasal saddles. In goodness‐of‐fit tests of time‐dependent models for local survival, we only detected the presence of transients among young females in the Loire estuary, which indicated that this category of individuals includes an ‘unstable compartment’ continuing its migratory journey further to the south. We observed low monthly local survival and high emigration rates (range: 0.01‐0.81) in both areas, which suggests high turnover rates. In the Loire estuary, temporal changes in emigration rates matched the post‐ and pre‐nuptial migration peaks (i.e. October‐November and February‐March). By combining local survival probabilities and count data, we derived an estimate of the ratio between the winter peak count of teals in our study areas and the minimum number of birds that actually frequented the areas over the entire wintering period (October‐March). In both cases, we estimated the number of teal visiting the two wintering sites be about twice as large as the maximum number of birds counted instantaneously.
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