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Invasive rats and seabirds after 2,000 years 1633

Methods (Table 1). Because they possess life-history traits
likely to make them particularly sensitive to intro-
Datasets duced mammal predators (Jones et al. 2008), we
focused seabird analyses on the four Mediterranean
We focused our study on the Western Mediterranean Procellariiform taxa: the Yelkouan shearwater
Basin because it has been more studied than the eastern (Puffinus yelkouan) and the Balearic shearwater
part. The Western Mediterranean Basin stretches from (P. mauretanicus), which are Mediterranean endemic
the Gibraltar Strait (west) to the Adriatic Sea (east), species, and two Mediterranean endemic subspecies,
and covers about one-third of the 3,081,880 km 2 the Mediterranean Cory’s shearwater (Calonectris
Mediterranean Sea and comprises ca. 700 islands and diomedea diomedea) and the Mediterranean storm
islets. Although available, data about island charac- petrel (Hydrobates pelagicus melitensis). The Cory’s
teristics, seabirds, and rats have never been compiled shearwater is the largest species (500–800 g) and its
and analyzed on such a wide scale (but see Martin et al. distribution encompasses the entire Mediterranean
2000). The data used in this review were collated from Basin (57,000–76,000 breeding pairs, Zotier et al.
published sources (including grey literature), unpub- 1999). Its breeding colonies on islands range from
lished reports, notes, and personal communication small (\20 breeding pairs) to large (e.g., 25,000
from nature-reserve managers, conservationists, and breeding pairs on Zembra Island, Tunisia; Isenmann
researchers, who were specifically contacted. and Moali 2000). The distribution of the Yelkouan
Data on seabird presence and abundance, island shearwater (350–500 g) is sparse and the world
characteristics, and ship rat presence were collected population may be limited to only a few thousand
for 292 islands (Fig. 1; Appendix 1). Only the most breeding pairs (Bourgeois and Vidal 2008). Yelkouan
recent and reliable census on breeding seabird shearwater colonies are generally quite small but can
populations was used. For each of these islands, five reach up to 1,300–8,600 pairs on Tavolara-Molara
potential explanatory variables for rat presence and islands, Sardinia (G. Spano and N. Baccetti, pers.
seabird presence and abundance were also collected comm.). The Balearic shearwater (349–416 g) is

Fig. 1 Map of the Western
Mediterranean and location
of the 292 islands studied

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