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Patterns in the Provisioning and Growth of Nestling Rhinoceros Auklets

D. F. Bertram, G. W. Kaiser and R. C. Ydenberg
The Auk
Vol. 108, No. 4 (Oct., 1991), pp. 842-852
Stable URL: http://www.jstor.org/stable/4088313
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Patterns in the Provisioning and Growth of Nestling Rhinoceros Auklets
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Abstract

We studied (1983-1987) the provisioning and growth of nestling Rhinoceros Auklets (Cerorhinca monocerata) in a breeding colony on the Lucy Islands and measured growth (1984-1986) in other colonies also on the British Columbia coast (Pine Island and Triangle Island). There were strong differences in the pattern of provisioning among the three years. In 1985 provisioning peaked around the midpoint (30 days) of the nestling period and then declined rapidly. In 1986, provisioning also declined after the midpoint, but more slowly than in 1985. In 1987, provisioning remained approximately constant during the entire breeding season. We found no evidence that late-hatched chicks were consistently fed less than early-hatched chicks, though the statistical power of the tests made to detect this difference was low. There were significant annual differences in chick growth. Growth was fastest in 1985, intermediate in 1984 and 1986, and slowest in 1983 and 1987. The mean growth rate on the three colonies changed in unison from year to year. Hypotheses based on seasonal environmental changes and on systematic changes in the food requirements of growing chicks do not explain the observed patterns. Our data on chick growth and independent data on ocean production suggest that the two varied directly and in unison among years. However, provisioning in the latter part of chick development did not appear to reflect directly the quality of ocean feeding conditions. We conclude that although large-scale fluctuations in ocean production are likely to be the dominant influence upon provisioning, the manner in which parents respond to such variation is poorly understood.

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