Diet and survival of capercaillie Tetrao urogallus chicks in Scotland

The diet of young capercaillie Tetrao urogallus chicks in Scotland was asse ssed from analysis of their faeces, collected at the roost sites of broods with radio-marked mothers. Lepidoptera larvae were their main invertebrate food and bilberry Vaccinium myrtillus their main plant food. The concentrat ion of larval remains in the chicks' droppings was correlated with the abun dance of larvae found by sweep netting in nearby vegetation. Broods of chic ks with the greatest concentration of larval remains in their droppings sur vived best. Sweep netting for larvae in a semi-natural pine forest in June 1991-1996 showed that larval size, abundance and timing differed among year s, and that the sites with the most larvae also differed from year to year. In the same forest, we estimated capercaillie breeding success from hens a nd chicks found during dog counts. The average number of young per hen in J uly was correlated with the size, rather than the abundance, of larvae in m id June.