Document: MAR-3-82-22

Current consequences of an ancient introduction: Rats, island characteristics and colonial nesting birds in the Mediterranean.

MARTIN, J.* ¹, J.THIBAULT ² and V.BRETAGNOLLE ³

CEFE/CNRS, Montpellier cedex, France ¹
Parc Naturel Regional de Corse, Ajaccio, France ²
CEBC/CNRS, Beauvoir-sur-Niort, France ³

Abstract:
The devastation of island faunas by alien species has been instrumental in raising concerns about the global threat to biological diversity. Colonial nesting species, often restricted to islands, have been severely impacted. Eradication of introduced species, used as a means to alleviate the problem, is usually done with little or no understanding of the mechanisms governing interactions between introduced and native species. We analyze how island area, rock substrate, bird species biology and presence of an introduced species, the Black rat Rattus rattus, interact to explain the distribution and abundance of colonial nesting birds on a set of 72 islands from six archipelagos in the Western Mediterranean. Rats were introduced to this region over 2000 years ago and these communities have had time to reach an equilibrium. Rats have more affected species distributions on the smaller islands, and on islands with an acidic or neutral rock substrate (coarse texture), than those with limestone, and smooth texture. The smallest species are most sensitive to rats, are often absent from islands with rats, and are systematically absent on islands with rats and a coarse structured rock substrate. On the smaller islands, where rat densities are highest, larger colonial birds are negatively affected. On larger islands, where rat densities are lower and fluctuating from year to year, larger colonial birds can maintain healthy populations despite the presence of rats. Although rats caused local extinction or reduction in bird abundance, the presence of islands varying in size and/or substrate allowed most archipelagos to retain their suite of colonial nesting bird species, despite a presumably reduced abundance for most species.

Keywords: introduced species, colonial birds, island area, body size, rock substrate

This abstract is being presented at: 3:30 PM in session:
Oral Session #14: Disturbance Effects on Bird Populations.