Kingfisher (Alcedo atthis) diet and prey selection as assessed by the analysis of pellets collected under resting sites (River Ticino, north Italy)

The diet of the kingfisher Alcedo atthis is usually studied by collecting pellet pools from the nest after breeding. This collecting method is very efficient but has some drawbacks which include invasiveness and restriction to the reproductive period. To overcome these limits, here we propose the collection of pellets under resting sites. Although requiring a large number of surveys to find suitable resting sites and obtain sufficient sample size, this method is minimally invasive and allows a precise estimate of the relative frequency of prey items per pellet and the assessment of kingfisher diet also outside the breeding period. The methodology was applied to an Italian kingfisher population (River Ticino, northern Italy) between March and October 2019. Resting sites were identified in 15 out of 54 sampling stations, from which 133 pellets were collected. By comparing diagnostic remains, 478 preyed individuals were identified including mainly fish (94.4%) ranging in total length between 21 and 105 mm. Fish availability of the River was assessed. The fish community included 49 species, of which 22 (45%) were non-native. Kingfishers preyed on the most widespread and abundant native species, while the contribution of exotic fish was lower than expected. However, the overall consistency of prey use and availability suggests that the analysis of kingfisher pellets represents an additional method for monitoring the composition of freshwater fish communities and man-induced changes across broad geographical scales.