Chick mortality in European Shag Stictocarbo aristotelis related to food limitations during adverse weather events.

European Shag (Phalacrocorax aristotelis) Science Article 3


This study analyses the mortality of chicks of the European Shag Stictocarbo aristotelis in the Cies Islands (NW Spain). Chick mortality on this island is the main cause of the yearly variation in chick production. By visiting the nests after hatching occurred we determined the periods of high mortality in four years of study. The weather conditions, especially rain and wind, during these periods were significantly more adverse than in the periods showing no mortality. There was a significant relationship between the yearly mortality rate in chicks and the number of windy and rainy days during the growth period of the chicks (May) during four years of study. The physical quality of the nest site during the four seasons of study was similar between nests affected by mortality and those that were not. In the colony we studied, feeding is almost exclusively by co-operative groups capturing sandeels, with this prey accounting for over 70% during the breeding season. During a period of he avy rains in 1997, the sandeels were found to be present in only 22% of the pellets and during this time co-operative fishing groups were not recorded. The most important factor involved in the mortality would appear to be food limitation

Velando A., Ortega-Ruano J.E. & Freire J., ARDEA 87 (1): 51-59

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