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

The Grey-headed woodpecker (<i>Picus canus</i>) 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 <i>P. canus</i> 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 <i>P. canus</i>. From these, we collected faeces samples totalling 94 conical tubes of 1.5 ml each, obtained from 17 nest boxes used by <i>P. canus</i> 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 <i>P. canus</i> 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 <i>P. canus</i>.