Altitudinal migration in American Dippers (Cinclus mexicanus): Do migrants produce higher quality offspring?
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| Authors: | Mackas, RH; Green, DJ; Whitehorne, IBJ; Fairhurst, EN; Middleton, HA; Morrissey, CA |
| Year: | 2010 |
| Journal: | Canadian Journal of Zoology-Revue Canadienne de Zoologie 88: 369-377 Article Link (DOI) |
| Title: | Altitudinal migration in American Dippers (Cinclus mexicanus): Do migrants produce higher quality offspring? |
| Abstract: | Breeding at high elevations can favour life-history strategies in which parents shift to investing in higher quality rather than higher numbers of offspring. In American Dippers (Cinclus mexicanus Swainson, 1827), altitudinal migrants produce fewer fledglings than sedentary individuals (residents) that breed at lower elevations. We examined whether migrants compensate for their lower fecundity by providing their offspring with a higher quality diet and (or) more food, and producing higher quality offspring. Nestling diet was assessed using observations and stable isotope analysis of feathers grown during the nestling period. Nestling quality was assessed using a condition index (residuals from a mass tarsus regression) and postfledging survival. We found that migrants fed their offspring less fish, and despite having higher feeding rates, had lower energetic provisioning rates than residents. Migrants also produced offspring that were in worse condition and had lower postfledging survival. This study found no evidence that altitudinal migration is associated with a trade-off favouring the production of smaller numbers of higher quality young. Instead our data provide support for the hypothesis that altitudinal migration in American Dippers is an outcome of competition for limited nest sites at lower elevations that forces some individuals to move to higher elevations to breed. |
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