Altruism in the Savannah sparrow?

1. Six of eight male Savannah sparrows removed from their territories just prior to their eggs hatching were replaced by new individuals. While the ensuing behavior of all but one replacement bird might be considered altruistic, such behavior is interpreted as a response to an artificial situation occurring infrequently naturally. Since the response would normally be advantageous (when the female was the male's mate) and rarely disadvantageous, maintenance of the response is evolutionarily favored. 2. Contrary to the suggestion that the sequential hormonal changes accompanying breeding have been selected for as a means to minimize altruistic errors, we argue that any advantage so derived would be coincidental rather than the primary selective force.