30ºW
20ºW
10ºW
40ºN
A Z O R E S Corvo
Graciosa
Berlengas
Santa Maria A R C H I P E L A G O M A D E I R A
Figure 5.5
30ºN
Desertas A R C H I P E L A G O Selvagens C A N A R Y
Main areas of data-logger use
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c. Effects of the devices on birds The studies that involve attaching devices to seabirds result in a stressing effect inherent to the attachment method and may condition the behaviour and performance of the bird when looking for food on the high sea (Wilson & McMahon 2006). In order to quantify that possible impact, all birds processed during this work were weighed after returning from their feeding trip, as birds were expected to return heavier. The large majority (>90%) of individuals sampled maintained or increased their weight during the study. According to these results, no negative effects were found on the birds sampled. This study thus yielded similar results to those obtained in previous work with Cory's Shearwater (Igual et al. 2005) and other seabirds (Cairns et al. 1987, Garthe et al. 2003).
Cory´s Shearwater with compass-logger attached at its central tail feathers
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Important Areas for Seabirds in Portugal