Winter food sources for the Grey-headed Woodpecker (Picus canus) in South Korea using faecal analysis in nest boxes

The Grey-headed woodpecker (Picus canus) inhabiting South Korea is an insectivorous bird species that favours ants. However, during winter, most insects enter a dormant stage, reducing their availability as food sources. This may prompt P. canus to change its primary food sources. To verify this hypothesis, we fabricated and installed 91 nest boxes in forests in Seocheon-gun, Chungnam Province, considering the body size of P. canus. From these, we collected faeces samples totalling 94 conical tubes of 1.5 ml each, obtained from 17 nest boxes used by P. canus as roosting sites. The collected faeces samples were examined under a microscope and their relative frequencies were calculated at the family or order level. Formicidae exceeded 70%, confirming it as the primary food source for P. canus during the breeding season and also in winter. Anacardiaceae fruits accounted for approximately 16%, significantly lower than Formicidae, but still considered a major winter food source for P. canus.