NOTE / NOTE Introduced predators and cavity-nesting seabirds: unexpected low level of interaction at breeding sites L. Ruffino, K. Bourgeois, E. Vidal, J. Icard, F. Torre, and J. Legrand Abstract: The mechanisms by which introduced predators and long-lived seabirds interact and even coexist are still poorly known. Here, the interactions between the widely introduced black rat (Rattus rattus (L., 1758)) and an endemic Mediter- ranean cavity-nesting seabird, the yelkouan shearwater (Puffinus yelkouan (Acerbi, 1827)), were for the first time investi- gated for a set of 60 suitable breeding cavities throughout the entire breeding cycle of this seabird. Our results pointed out that rat visits to cavities were significantly higher when shearwaters had left the colony for their interbreeding exodus. Among the set of suitable breeding cavities, yelkouan shearwaters preferentially selected the deepest and the most winding cavities for breeding. Very few rat visits were recorded at the shearwater-occupied cavities and no predation event was re- corded. These intriguing results reveal a low level of interaction between introduced black rats and yelkouan shearwaters, which may have facilitated their long-term coexistence for thousands of years on some Mediterranean islands. Re ´sume ´: Les me ´canismes d’interaction et notamment de coexistence entre pre ´dateurs introduits et oiseaux marins longe ´- vifs sont encore peu connus a ` l’heure actuelle. Ici, les interactions entre le rat noir (Rattus rattus (L., 1758)), espe `ce large- ment introduite sur les ı ˆles de la plane `te, et un oiseau marin longe ´vif ende ´mique de Me ´diterrane ´e a ` nidification hypoge ´e, le puffin yelkouan (Puffinus yelkouan (Acerbi, 1827)) ont e ´te ´ pour la premie `re fois e ´tudie ´es sur un lot de 60 cavite ´s favor- ables a ` la reproduction du puffin tout au long du cycle de reproduction. Nos re ´sultats ont montre ´ que les visites de cavite ´s par les rats sont significativement plus importantes lorsque les puffins ont quitte ´ les colonies durant la phase internuptiale. Parmi l’ensemble des cavite ´s favorables a ` la reproduction, ce sont les cavite ´s les plus profondes et les plus sinueuses qui sont pre ´fe ´rentiellement utilise ´es par les puffins. Tre `s peu de visites de rats ont e ´te ´ enregistre ´es dans les cavite ´s occupe ´es par les puffins et aucun phe ´nome `ne de pre ´dation n’a e ´te ´ observe ´. De manie `re inattendue, ces re ´sultats te ´moignent d’un fai- ble degre ´ d’interaction entre les rats noirs introduits et les puffins yelkouan, ce qui pourrait avoir facilite ´ leur coexistence pluri-mille ´naire sur certaines ı ˆles de Me ´diterrane ´e. Introduction Mammalian predators introduced on islands are known to have severely depleted populations of native species, leading some, especially birds, to extinction or local extirpation (e.g., Owens and Bennet 2000; Courchamp et al. 2003). Rats (genus Rattus G. Fischer, 1803) are among the most successful predators introduced on islands worldwide, mak- ing them one of the largest plagues for island avifauna, es- pecially for small and medium-sized petrels (Moors and Atkinson 1984; Atkinson 1985; Jones et al. 2008). Conse- quently, numerous cases of breeding failures, sharp decreases in breeding population, and local extirpations have been reported after rat introduction on islands (At- kinson 1985; Towns et al. 2006). Even if the effects of introduced rats on seabird populations are generally consid- ered to be well-known, the mechanisms by which they inter- act are still under debate (Courchamp et al. 2003; Towns et al. 2006). Indeed, as predation is a cryptic phenomenon, direct observations of predation by rats are extremely diffi- cult in the field, especially for cavity and burrow-nesting birds (Norman 1975; Johnston et al. 2003; Towns et al. 2006). However, according to their predatory-foraging behaviour, we can hypothesize that rats may visit petrel burrows significantly more during the breeding period of birds, especially when birds are the most vulnerable (i.e., egg-incubating and chick-rearing periods), compared with the bird interbreeding exodus period. From an evolutionary point of view, recent theories (i.e., evolutionary and ecological trap concepts) suggest that in- digenous species that have long evolved without predators may fail to rapidly evolve or learn mechanisms to cope Received 9 July 2007. Accepted 8 May 2008. Published on the NRC Research Press Web site at cjz.nrc.ca on 5 September 2008. L. Ruffino, 1 K. Bourgeois, E. Vidal, J. Icard, F. Torre, and J. Legrand. Institut Me ´diterrane ´en d’Ecologie et de Pale ´oe ´cologie (IMEP) – Centre National de la Recherche Scientifique (CNRS), Unite ´s Mixtes de Recherche (UMR) 6116, Paul Ce ´zanne University, Ba ˆtiment Villemin, Domaine du Petit Arbois, Avenue Philibert – B.P. 80, 13545 Aix-en-Provence CEDEX 04, France. 1 Corresponding author (e-mail: ruffino_lise@yahoo.fr). 1068 Can. J. Zool. 86: 1068–1073 (2008) doi:10.1139/Z08-070 # 2008 NRC Canada