Communal Behaviors Of The Smooth-Billed Ani (crotophaga Ani)

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)




In a three year field study on the communal behaviors of the Smooth-billed Ani (Crotophaga ani) in south Florida I have studied three major topics: egg-burying behavior, the role of non-breeding helpers, and factors selecting for the evolution and maintenance of group living.Egg-burying behavior was discovered as a method by which late-laying females destroy the eggs of earlier laying females at communal nests. First-laying females in groups with less than four laying females are partially compensated for egg-burial by the higher survival rates of their nestlings. The results of a manipulative experiment suggest that egg-burying behavior may have evolved from an ancestral response to intraspecific egg parasitism.Ani juveniles remain on their natal territories and help in rearing subsequent broods for up to one year. Helpers are involved in all breeding behaviors except incubation and provide significant help by decreasing the amount of nestling feeding done by adults.Several factors which might help explain the evolution of communal living in Smooth-bills were examined. When feeding, large groups have sentinels in position a higher proportion of the time than small groups. In addition, members of large groups spend less time as sentinels than individuals in small groups. This increase in sentinel protection with increasing group size and the concurrent decrease in any risk involved in being a sentinel, may lead to higher individual survival rates in larger groups than in small ones. Group size has no significant effect, however, on feeding, growth or reproductive rates. Another factor which might have been important in leading to communal breeding is the 'gang effect.' Large groups can annex all or part of the territories of smaller groups thus providing an additional potential advantage in terms of food, roost site and nest site availability for individuals in large groups.


Biology, Zoology

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