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1640 L. Ruffino et al.

unable to be covered in this review (because of suitable for breeding, following rat eradications
paucity of accurate data), yet these two parameters (Veitch and Clout 2002; Towns et al. 2006). In the
are expected to determine the magnitude of the Mediterranean, few eradication attempts have been
increase in shearwater breeding success and thus the carried out on islands in the past 20 years, and most of
success of a rat-removal program (Jouventin et al. these were restricted to islands \10 ha (L. Ruffino
2003; Igual et al. 2006). When rat densities are high, unpublished data). Today, island managers are pro-
the increase in seabird breeding success after rat vided with a variety of powerful methods to eradicate
removal is expected to be sharper than for colonies rats and mitigate non-target effects and secondary
where rat densities are low and, similarly, benefits poisoning events. Moreover, island area may no
from rat removal should increase with control effort longer be a limiting factor for rat eradications.
(Igual et al. 2006). Howald et al. (2007) reported 159 successful ship
Overall, few studies have been published on rat rat eradications worldwide, 14 of them conducted on
impact on Mediterranean Procellariiformes (Table 5), islands larger than 500 ha. Conservation managers are
especially on the storm petrel, although this species now also able to remove rats from large and biolog-
seems to be the most vulnerable to rat impact. This ically complex islands. They also manage to eradicate
lack of data may be due to the difficulty of taking rodents that have been introduced on islands for
census, monitoring, and hence evaluating signs of hundreds of years (e.g., Rattus exulans on New
population changes for this cryptic species. In many Zealand islands; Howald et al. 2007). The main
cases, unfortunately, reports of rat impact on challenges for Mediterranean island managers, then,
seabirds were circumstantial and equivocal, and may be to deal with social, ecological, and funding
sometimes too subjective to allow for clear infer- issues. Because most Mediterranean islands are
ences on the real magnitude of rat impact. Moreover, inhabited and closely linked to main islands and
as predation is a cryptic phenomenon, it is often continents by human transport and activities, appro-
difficult to make direct observations of predation by priate environmental education and means of
rats in the field, especially for burrow-nesting birds preventing reinvasions are required. Furthermore,
(Towns et al. 2006) and to distinguish predation Mediterranean island systems house non-target verte-
events from the consumption of neglected eggs or brate species with high conservation value that need to
carrion provided by natural death (Norman 1975; be considered when planning eradication programs,
Towns et al. 2006; Quillfeldt et al. 2008). At present, but which are expected to benefit from rat removal. As
there is an urgent need to collect more data on the Mediterranean islands are currently under increasing
breeding biology of the four Mediterranean burrowing pressure from various human activities, any manage-
seabirds throughout the Mediterranean basin, to ment operations that would improve seabird
perform long-term studies, and rigorously monitor population health should be promoted.
breeding success of seabirds before and after conser-
vation measures and to routinely quantify rat impact
on their productivity with standardized methods. Conclusions

Conservation implications The Mediterranean context is particularly intriguing,
since the survival of the four Mediterranean Procel-
Over the past 10 years, eradication of invasive species lariiformes after 2,000 years of ship rat presence on
has become a powerful tool in preventing further islands seems to go against the current global threat to
extinctions and for restoring native island ecosystems burrowing seabirds from rat impact (Atkinson 1985;
(Veitch and Clout 2002; Towns et al. 2006; Howald Birdlife International 2000; Jones et al. 2008). Thus,
et al. 2007). In particular, seabird communities have the apparent paradox of long-standing coexistence
clearly benefited from the removal of introduced rats between rats and seabirds raises some new conserva-
from islands worldwide. Indeed, many studies report tion questions, especially regarding the ability of
a significant increase in breeding success of seabirds native island species to ‘‘coexist’’ with introduced
or new breeder establishment on islands once again rats. Sound understanding of the mechanisms of such

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