Impact of feral cat and fox on Socrota cormorant on Siniya Island

Muzaffar, S. B., Benjamin, S., & Gubiani, R. E. (2013). The impact of fox and feral cat predation on the population viability of the threatened, endemic Socotra cormorant on Siniya Island, United Arab Emirates. Marine Ornithology, 41, 171-177.

Seabirds are vulnerable to a variety of threats occurring at breeding colonies, including disturbance, habitat degradation and predation from terrestrial predators. Socotra Cormorants Phalacrocorax nigrogularis are threatened, regionally endemic seabirds restricted to the Arabian Gulf and Gulf of Oman regions. Populations have been collapsing throughout their range, mostly in response to habitat loss from oil exploitation and disturbance at breeding sites. Almost half of the historically abundant colonies have disappeared, and the global breeding population has suffered catastrophic declines over the last 30 years. Siniya Island, Umm Al Quwain, hosts the largest colony in the United Arab Emirates with an estimated 15 500 breeding pairs. Predation by feral cats Felis catus and native red foxes Vulpes vulpes constitutes a major threat to this colony. We simulated population trends under different mortality levels using the software Vortex. The baseline model was parameterized using data on Socotra Cormorants or other cormorant species. Simulation of the baseline model showed a gradual increase in population, assuming carrying capacity of Siniya Island was 50 000 individuals. Compared with the baseline, within 50 years, a mortality of 900 individuals per year would reduce the population to fewer than 5 000 breeding pairs; mortality of 1 800 or 2 000 individuals per year would reduce the population to a few hundred pairs. Populations were more susceptible to adult mortality in all mortality scenarios (900, 1 800, and 2 000 individuals/year), leading to reductions to near-extinction levels. Our estimates of predation-related mortality were conservative, and the trends implied by the population model could potentially be catastrophic to the species. Eradication of feral cats and red foxes is recommended as a management tool to ensure long-term survival of this colony