The Common Kingfisher Alcedo atthis is a fish-eating predatory bird that is reported to prey mainly on pelagic, benthic, or both types of fish prey. It still remains unclear whether the species has the capacity to prey indistinctly on all types of fish, regardless of their position within the water column. The aim of our study was to test if kingfishers are able to select particular fish prey or if, by contrast, they feed on the most abundant and accessible fish. We identified the fish prey consumed by kingfishers at 14 nests in total, and also sampled, using electrofishing surveys, fish prey availability on the river stretches where the nests were located. We used Savage's index in order to check whether there was prey selection. Overall, kingfishers preyed upon eight fish species: Bermejuela Acondrostoma arcasii, Bleak Alburnus alburnus, Pyrenean Stone Loach Barbatula quignardi, Ebro Barbel Luciobarbus graellsii, Pyrenean Gudgeon Gobio lozanoi, Ebro Nase Parachondrostoma miegii, Pyrenean Minnow Phoxinus bigerri, and Brown Trout Salmo trutta. The most consumed prey were pelagic species (Pyrenean Minnow and Brown Trout). These results suggest that the Kingfisher preys on pelagic species because of their accessibility and avoids bottom-dwelling species, which may remain hidden from this predator, kingfishers preyed mostly on fish of 50 to 60 mm in length, but mean size values varied prey-specifically, possibly because of the vertical specific distribution in relation to the fish age and species and, finally, prey availability.
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