Effects of Caching Supplemental Food on Induced Feather Regeneration in Wintering Gray Jays Perisoreus canadensis: A Ptilochronology Study

Abstract

The technique of ptilochronology was used to assess the influence of food cache availability on feather regeneration in Gray Jays Perisoreus canadensis wintering in northcentral Alaska (66'40'N, 150033'W). The method involved plucking a rectrix (tail feather), allowing the bird to grow a replacement feather from the same follicle, plucking that induced feather, and then measuring the width of daily growth bars and the length and mass of the induced feather. The experimental protocol involved supplementing jays in some territories with food that they were allowed to cache, and leaving jays in other territories unsupplemented. After the period of food supplementation, a rectrix was taken from jays in all territories. Approximately two months later, the induced (replacement) rectrix was taken from jays in all territories. Replacement feathers from jays with supplemental caches grew at a faster rate and were longer and heavier than those from jays that did not have access to supplemental caches. Supplemented jays were also more likely to grow a replacement feather. These results suggest that the wintering jays with access to more cached food were able to allocate a greater amount of energy to feather growth. Ptilochronology appears to have promise for improving the experimental tractability of a great variety of questions in avian ecology.