Lonnie et al. • POPULATION SURVEY OF LEACH'S STORM-PETREL 
251 
were breeding on Grand Colombier Island during 
our survey (Lonnee et al. 2008; Table 1). The 
temporal trend of the gull population on Grand 
Colombier Island is not well known but no major 
increase seems to have occurred recently. Thus, 
the impact of the gull population on Leach's 
Storm-Petrels is likely limited. Wc also found 
occasional eggs inside burrows and dead chicks at 
burrow entrances predated, presumably by mead¬ 
ow voles, during our survey. 
Another potential threat to the Leach's Storm- 
Petrel breeding population on Grand Colombier 
Island could arise from increase of the breeding 
population of Atlantic Puffins. The number of 
puffin breeding pairs dramatically increased during 
the last several decades, from —400 pairs in the late 
! 970s (Desbrosses and Etc he berry 1989) to > 1,000 
in 2004 (R. L. Bryant, unpubl. data) and reached 
9,543 ± 1,2.16 in 2008 (Lormec el al. 2008). This 
increase was paralleled by colonization of new 
sectors on Grand Colombier Island, including slope 
habitats which arc also favored hy Leach's Storm- 
Petrels. Puffins dig large burrows and eject the 
excavated soil around the nest, resulting in fern 
disappearance and a marked reduction in vegetation 
cover, making habitats unfavorable for LeacITs 
Storm-Petrels. Sowls el al. (1980) reported similar 
destruction of nesting habitat of Leach's Storm 
Petrels through competition with Cassin's Anklets 
(Ptychoramphus ah’ttiiats) and Double-crested 
Cormorants (Phalacrocorux auritus). The spatial 
colonization and population trend of Atlantic 
Puffins breeding on Grand Colombier Island should 
be carefully monitored in future years to detect and 
quantify potential competition for breeding habitat 
w ith Leach’s Storm-Petrels. 
ACKNOWLEDGMENTS 
We thank Philippe Casadei and Marjorie Jouglet for help 
during surveys. We thank Vincent Brctagnolle for access to 
song recordings and Andre Mariam for technical advice. 
We sincerely thank Cyril Fraud lor help with statistical 
analyses. We are grateful to the staff of the regional 
delegation of Office National de la Chasse et de la Faune 
Sauvage (ONCFS) overseas for logistic facilities. The work 
was supported by Direction de P Agriculture et des Forets of 
Saint Pierre et Miquelon and by ONCFS. 
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