Survival of Slender-billed Gull chicks during the crèching period

Chokri, Mohamed Ali; Hammouda, Abdessalem; Tavecchia, Giacomo

Survival of Slender-billed Gull chicks during the crèching period

2011

Chokri, Mohamed Ali | Hammouda, Abdessalem | Tavecchia, Giacomo

Capsule Crèches formed early in the season lasted longer than those formed later, but a longer crèching period did not appear to confer higher chick survival.Aims To investigate the ecological factors influencing the benefit to parents of crèching behaviour by measuring chick survival.Methods Mark–recapture was used to model apparent daily survival of 505 chicks during the crèching period in three different crèches. We contrasted models with different tipping points to assess possible differences across crèches in chick survival during the first week and in the moment at which chick departures began.Results We did not find a clear difference across crèches on daily chick survival during the first stages of the crèche. By modelling chick apparent survival as a linear function of time we showed that the latest formed crèche dispersed more rapidly.Conclusions The two crèches formed early in the season lasted longer than the one formed later but chicks did not appear to have a higher survival over the first week of crèching. We suggest that a longer period at the crèche should result in a higher survival in the period soon after fledging because chicks leave the crèche 4–7 days older than other chicks. Furthermore, early crèches are synchronous with those of other species breeding in the same area, thus perhaps diluting predation. We discuss the limitations of our analysis and the possible implications for the community of waterbirds breeding at our study site.

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