LEPIDOPTERA LARVAE AS FOOD FOR CAPERCAILLIE CHICK (TETRAO-UROGALLUS) - A FIELD EXPERIMENT

Lepidoptera larvae are important prey for capercaillie chicks (Tetrao urogallus), but utilization varies among habitats. This held experiment investigates the effects of larval feeding behaviour, abundance and the density of bilberry (Vaccinium myrtillus) on utilization of larvae by a group of four capercaille chicks and also tests whether chick utilization differs between wet and dry coniferous forest. In fenced plots, four hand-raised chicks were released for a 15 min feeding period. Reduction of geometrid larvae was correlated positively with their abundance but correlated negatively with bilberry density. Geometrids had a much higher predation risk than pyralids and tortricids, probably because they are exposed while feeding, in contrast to pyralids and tortricids. Total reduction of lepidoptera was higher in wet than dry forest, probably due to a higher proportion of geometrid larvae, and lower density of bilberry in the wet forest. The manner of insect feeding and habitat type (e.g. wet and dry forest), which influence bilberry density, therefore may be important factors to consider when assessing or managing habitat quality for capercaillie chicks.