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1 October 2001 Timing of Mineral Sequestration in Leg Bones of White-tailed Ptarmigan
James R. Larison, J. G. Crock, Christine M. Snow
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Birds are unique among vertebrates in that they protect their eggs with rigid, calcium-rich shells. Thus, for a short period of time during the annual reproductive cycle, birds experience extraordinarily high demands for calcium. Two strategies appear to exist for meeting those temporally high demands. Some birds apparently seek out calcium-rich foods immediately prior to and during egg laying whereas others may store calcium in their skeletons over a much longer period of time, mobilizing those reserves only when they are needed for production of eggshells. In this study, we used dual energy, X-ray absorptiometry and inductively coupled plasma mass spectroscopy to monitor annual shifts in bone mineral content in the legs of White-tailed Ptarmigans (Lagopus leucurus). The study organisms were known to live on calcium-poor soils. Despite an apparent shortage of calcium in their diets, the test subjects stored substantial amounts of calcium in their leg bones in months prior to reproduction. Those stores were subsequently depleted during the egg-laying period. We suggest ability to store calcium in the skeleton may afford this species more flexibility in selecting suitable breeding habitats than would be possible otherwise.

James R. Larison, J. G. Crock, and Christine M. Snow "Timing of Mineral Sequestration in Leg Bones of White-tailed Ptarmigan," The Auk 118(4), 1057-1062, (1 October 2001).[1057:TOMSIL]2.0.CO;2
Received: 13 October 2000; Accepted: 11 June 2001; Published: 1 October 2001
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