Human disturbance in Western Gull Larus occidentalis livens colonies and possible amplification by intraspecific predation

Indirect evidence is presented that human disturbances are having a profound effect on reproductive efforts of Larus occidentalis livens at several colonies in the Gulf of California. Breeding adults that lose their eggs or chicks apparently practise conspecific predation whether or not humans are present, thus increasing effects of human intrusions. These combined effects could lead to a severe decline in numbers or even pose a threat to the survival of this endemic population, if human disturbance is widespread. Attempts to assess breeding success throughout the Gulf seem warranted and, if necessary, some action to regulate human contact may be essential.