Heermann's gull  (Larus heermanni)

Concentrated into just eight colonies within a small area, Heermann's gull is considered to be stable, but faces risks inherent in such a compact community. Ninety percent of the world's population is found on Isla Rasa in the Gulf of California so conservation of this island habitat is crucial to the survival of this species. It is estimated that there are 150,000 pairs of Heermann's gulls living today, and that their main threat is the increasing population of the yellow-footed gull (Larus livens) which is a predator of Heermann's gull eggs and chicks (2).

Very little specific conservation action is targeted at Heermann's gull because although its range is small and it is therefore vulnerable, the population is judged to be stable. It has proved extremely difficult to survey, producing wildly different population figures for each census. However, it is important to keep some idea of the population size in order to ensure that the yellow-footed gull is not impacting negatively on Heermann's gull (2). Ilsa Rasa became a sanctuary in 1964 (3).