Effects of helpers on breeder survival in the red-cockaded woodpecker (Picoides borealis) |
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Authors: | Memuna Z Khan Jeffrey R Walters |
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Institution: | (1) Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0406, USA,;(2) Present address: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA, e-mail: mkhan@princeton.edu, Tel.: +1-609-2586788, Fax: +1-609-2582712, |
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Abstract: | Helpers can gain future indirect fitness benefits by increasing the survival of breeders that produce offspring related to
the helper. Helping augments group size through the helper's presence and, in some cases, by increasing fledging success.
Breeders may then experience enhanced survivorship because of the benefits of living in large groups. Helping may also reduce
the workload of the breeder, which in turn may increase the likelihood that the breeder will survive to breed again. We used
Cox's proportional hazards model to examine whether breeders' survival in two populations of the red-cockaded woodpecker (Picoides borealis) was enhanced when group size was increased in the presence of (1) the helper itself, or (2) "extra" fledglings (fledglings
produced by the breeder because of helping behavior). We found that in the presence of helpers, the risk of a breeder dying
declined by 21–42% for males and 0–14% for females. Our results suggest reduced breeder workload as one mechanism to explain
reduced breeder mortality in the presence of helpers: breeders spent less time incubating and provisioning nestlings when
assisted by helpers. The risk of a breeder dying declined by 16–42% in males and 26–43% in females in the presence of "extra"
fledglings. We speculate on possible mechanisms by which fledglings might affect breeder survival. Our results support the
hypothesis that helpers gain future indirect benefits by reducing breeder mortality.
Electronic Publication |
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Keywords: | Red-cockaded woodpecker Picoides borealis Co-operative breeding Breeder survival |
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