Abstract

While many animals rely on stored food to survive periods of no or few resources, some of these species may also use cached food to feed young. The Canada Jay (Perisoreus canadensis (Linnaeus, 1766)) is a territorial, food-caching resident of North American boreal forests. Canada Jays have high winter survival when fresh food is rarely available and achieve high fledging rates before the return and breeding of most sympatric migratory passerines. Stored food must account for the Canada Jay’s winter survival, but it is less certain that stores are also used to feed nestlings. We conducted two experiments seeking evidence of such use, one using food marked with dye and a second using 15N-enriched glycine. Breeding pairs were supplemented with marked food in the pre-incubation period, followed by our attempts to find the marker in nestling feces (dye experiment) or feathers (15N-enrichment experiment). Both experiments provided evidence that at least some nestlings had ingested the marker, although the importance of this behaviour within the population remains unknown. Our study demonstrates how food markers can be used to infer feeding behaviour that has not been directly recorded in the wild, even after over 50 years of close observation.