Alternate Routes to Sociality in Jays—With a Theory for the Evolution of Altruism and Communal Breeding

Abstract

The social systems of New World species of jays are compared behaviorally and ecologically. Two lines leading to sociality are identified, one connecting the pair-in-territory system with the colonial system and a second connecting the pair-in-territory system with the communal system. Ecological factors in the evolution of communal breeding and its associated altruistic behavior are considered mainly in the genus Aphelocoma, but other birds are treated briefly. Three principal origins of communality and altruism in birds are identified: from colonies, from a surplus of males, and by retention of young in the family, the latter being of greatest importance. The theory proposed for the evolution of communal breeding and altruism emphasizes three main processes: 1) K-selection, (2) kin selection, and (3) kin-group selection in the same chronological order.