The colony of the Audouin's Gull at the Ebro Delta


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We describe the Audouin's Gull colony established in the Ebro Delta (NE Spain) since 1981. The amazing growth of this colony, which is now the largest in the worId, with about the 60070 of the species' world population, was favoured in our view both by the complete protection of the breeding areas from human interference since 1987, and by its high reproductive success (maximum 2.01 chieks/pair in 1988). This breeding success is the highest reeorded in Audouin's Gull eolonies studied to date, and it seems 10 be due to the high availability of feeding resourees (demersal fish) from activities by the loeal fishing fleet. Moreover, disturbanee by breeding Yellow-legged Gulls was low. Changes in these faetors eould break the eolony stability, as happened with the moratorium on inshore fishing in 1991 and 1992. The fragility of the Audouin's Gull population is mainly due to its generalized low breeding success in the main colonies, and its concentration in a few large eolonies.