Salivary Glands in the Gray Jays (Perisoreus)

Abstract

UNIQUE morphologic specialization in a single species or genus provides one of the best approaches into the entire subject of adaptation and the evolution of new groups. Further, if the animal possessing the unique specialization lives in an unusual or strenuous habitat, then the action of the evolutionary processes is frequently easier to understand. The gray jays of the genus Perisoreus form an excellent basis for the discussion of some of these problems as they are permanent residents in the far northern coniferous forests-one of the most strenuous habitats available to passerine birds. Gray jays must possess adaptations to the cold of winter and the ability to utilize the limited food supply available during the winter. The question of protection against the cold shall not be considered as I wish to concentrate on the problem of food gathering. This latter problem has been overlooked by ornithologists because the gray jays, like most other permanent residents in the northern forests, were not known to have any marked feeding adaptations. But the discovery of a pair of woodpecker-sized mandibular mucous glands in the gray jays reopens the question of their feeding habits. Mucous glands as large as those found in the woodpeckers are, to the best of my knowledge, not known in any other passerine bird. This leads to the question of whether this structure is a special adaptation in the gray jays for life in the northern coniferous forests. These questions cannot be answered directly because of a lack of information on the function and biological role of the glands, but I shall speculate on them because of their bearing on the general topic of adaptation of birds to the northern forests as well as their importance to the evolution of the gray jays.