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1 May 2009 Gang Brooding in Canada Geese: Role of Parental Condition and Experience
Michael R. Conover
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Some Canada Geese (Branta canadensis) raise their broods by themselves (two-parent families), while others raise them in gang broods, defined as two or more broods amalgamated into a single cohesive unit and shepherded by four or more parents. From 1984 to 2005, I individually marked Canada Geese in New Haven County, Connecticut, so that I could compare the characteristics of adults that raise their goslings in gang broods to those of adults that raised their goslings in two-parent families. I wanted to determine if a parent's decision to form a gang brood was influenced by its age or body mass, its own parents (indicating either that the behavior has a genetic component or that the behavior is learned while a gosling), its prior experiences raising broods, or the loss of its mate. Parents tended to use the same brood-rearing approach from one year to the next: 61% of parents of gang broods (i.e., gang-brooders) during one year also were gang-brooders the next year they had goslings; likewise, 65% of parents in two-parent families during one year raised their next brood in a two-parent family. Geese that changed mates from the previous year were more likely to switch brood-rearing approaches than those that stayed with the same mate. As geese gained more years of experience raising goslings, their propensity to form a gang brood increased; only 29% of geese raising broods for the first time formed a gang brood versus 80% for geese with 5 or more years of experience. Geese raised in gang broods themselves were no more likely than geese raised in two-parent families to form gang broods once they became adults and had their own broods. These results indicate that gang brooding is a behavior learned as an adult. I tested the hypothesis that adult geese attending the same gang brood are members of the same extended family but found that geese were as likely to form a gang brood with unrelated individuals as with siblings or parents.

© 2009 by The Cooper Ornithological Society. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website,
Michael R. Conover "Gang Brooding in Canada Geese: Role of Parental Condition and Experience," The Condor 111(2), 276-282, (1 May 2009).
Received: 4 November 2008; Accepted: 1 January 2009; Published: 1 May 2009

Branta canadensis
brood amalgamations
canada goose
cooperative breeding
gang broods
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