Abstract
AbstractThe largest colony of Cory's shearwaterCalonectris borealisnests on the island of Selvagem Grande in the north-eastern Atlantic. In 2002, a programme of eradication was conducted to remove two alien invasive mammals, the house mouseMus musculusand European rabbitOryctolagus cuniculus. Preliminary studies recorded beneficial effects of the eradications for a variety of plant and animal species, including Cory's shearwater. We recorded fledging rates of shearwaters for 1982–2001, prior to the eradication, and for 2002–2020, after the eradication, from two quadrats, each containing 134–329 nest sites. Although there was annual fluctuation in fledging rates in the quadrats, the mean rate of 40.74 ±SD 3.92 fledglings per 100 nest sites for the two quadrats combined prior to the eradication of mammals increased significantly, to 52.88 ± SD 5.03 per 100 nest sites, after the eradications. Because the two mammals were removed synchronously it is difficult to know which factors depressed fledging of Cory's shearwaters on Selvagem Grande. However, the predatory behaviour of house mice on other oceanic islands, and the fact that increased fledging was seen soon after the eradications occurred, suggest predation by house mice on shearwater hatchlings was the main cause of losses.
Highlights
T he Cory’s shearwater Calonectris borealis colony on the Portuguese island of Selvagem Grande has been the subject of study since the first scientific expedition to the island in (Pickering & Maul, )
This study has provided an opportunity to observe changes in the breeding biology of Cory’s shearwater of Selvagem Grande over a period of almost years
The mean number of chicks fledged after the removal of the alien invasive mammals ( . ± SD . ), was significantly greater than the mean number fledged before the event
Summary
T he Cory’s shearwater Calonectris borealis colony on the Portuguese island of Selvagem Grande has been the subject of study since the first scientific expedition to the island in (Pickering & Maul, ). The eradication began around the time of hatching in and fledging rates began to increase in that year This suggests that the effects of the invasive mammals were on hatchlings and developing chicks, rather than by disturbance of pairing, courtship, nest-building and egg-laying or direct predation of eggs. Study of the breeding Cory’s shearwater in the two quadrats has continued since the assessment of Zino et al ( ), and there are years of data since the removal of rabbits and house mice in We provide these additional data on fledging rates and confirmation of the beneficial impacts of the removal of rabbits and mice on this population of Cory’s shearwater and, probably, on the other, smaller and more vulnerable seabirds on the island. Selvagem Grande is an important breeding location for five pelagic seabird Species of European Conservation Concern (Oliveira & Menezes, ; BirdLife International, )
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