The role of floods in the lives of fish-eating birds: predator loss or benefit?
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Floods accompanied by high flow and high water turbidity are usually believed to cause problems to fish-eating birds and mammals searching visually for their prey. In the present study the diets of breeding kingfishers were studied during the normal river situation and during a long-lasting flood event with respect to diet composition, size of fish prey and food diversity index. During the normal situation (flow 1.75 m3 s−1, Secchi disc depth 0.5–1 m), the diet of a kingfisher was dominated by benthic fish species (52.9% by numbers, 63.9% by weight), the average size of fish taken was 6.5 cm L T and 3.0 g and the food diversity index reached its lowest value (1.57). In contrast, during the long-lasting flood event (flow 5–28 m3 s−1, Secchi disc depth 0.03–0.4 m) the diet of the kingfisher was dominated by sub-surface fish species (72.4% by numbers, 76.1% by weight) and both the average size of fish taken (7.4 cm L T and 3.7 g) and the food diversity index (1.83) increased significantly. The birds provided their nestlings with lower numbers of fish of larger sizes, which resulted in very similar weights of the young birds prior to fledging when the flood and normal situations were compared. This study provides evidence that in different foraging conditions the kingfishers adopt different foraging strategies to maintain their high breeding success.
KeywordsKingfisher Alcedo atthis Diagnostic bones Sub-surface species Benthic species Gudgeon Gobio gobio European chub Squalius cephalus
The authors thank M. Burgis for carefully reading and correcting the English and the Vltava River Authority, which kindly provided the river flow data. The study was supported by the Grant Agency of the Czech Republic (Project No. 206/09/P266), the Czech Union for Nature Conservation (Biodiversity Conservation Project) and UNCE (institutional resources of Ministry of Education, Youth and Sports of the Czech Republic for the support of science and research).
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