Field Trip Report: Solstice Canyon, 7 May, 2011 » 1 Woodpecker Acorn at hole_C Bragg 5-7-11 DSC00809

Acorn Woodpecker at the nest-hole. Solstice Canyon (C.Bragg 5/11)

Acorn Woodpeckers are one of the small but select species of birds which demonstrate the “helpers-at-the-nest” form of breeding behavior, i.e. the young of prior years stick around and help their parents with their new young. This species also build “granaries” – many small holes drilled into the trunk and limbs of one or more trees – for their acorns, which help them get through the winter when insects are hard to find. Such granaries can have over 10,000 holes and represent a tremendous investment of labor as each hole can take 30-60 minutes to drill. Because of the critical importance of the granary in enabling a family to survive, the territory is well-defended by the family, and any young bird inheriting such a territory has a tremendous survival advantage. Thus, scientists conclude, “helping-at-the-nest” evolved as a survival strategy, because young birds “inheriting” a territory with a granary after the death of one or both parents, was far more likely to survive than was a bird which left and was forced to establish its own territory and construct its own granary.