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Red-cockaded woodpeckers stash bone.

Female birds need calcium to product thick, protective eggshells, but they have trouble getting enough of it from a diet restricted to seeds and insects. So during the breeding and egg-laying season, they seek out calcium supplements, foraging for bits of bone, seashells and other items rich in the mineral.

Zoologists now report that female red-cockaded woodpeckers stash away bone fragments during the egg-laying season. This very preliminary observation, they say, marks the first known instance of a bird hoarding a substance for its mineral, rather than caloric, content.

Richard R. Repasky and his colleagues at North Carolina State University in Raleigh discovered the unusual behavior during a study of the endangered red-cockaded woodpecker (Picoides borealis) in the Sandhills, a very old pine forest in North Carolina. They report their findings in the latest issue of THE CONDOR (Vol.93, No.2).

The team tracked three female woodpeckers during egg-laying season and found that two of them gathered and hid bone fragments. They noted the behavior on only a couple of days before and during egg-laying. The females would spy a bone on the ground, land nearby, and consume flakes of it on the spot. The birds then carried larger fragments to a nearby tree and wedged them into the bark, retrieving the hidden fragments on several occasions during the egg-laying period, says Repasky.

While many birds cache food to help them through the lean season, these woodpeckers stored their calcium-rich finds despite a relative abundance of bone fragments and raptor pellets, hair-and-bone balls regurgitated by birds of prey. The habit may hark back to a primitive instinct, Repasky speculates: Egg-laying woodpeckers can avoid a risky trip to the forest floor by hiding their calcium supplements in trees. Birds pecking away at the ground make an easy target for hawks, owls and other predators, he notes.
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Title Annotation:birds hoard material for its calcium content
Publication:Science News
Date:Aug 31, 1991
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