Variations in calcium use by birds during the breeding season

During the breeding season birds need increased amounts of dietary calcium during egg laying and nestling rearing. Passerines acquire calcium shortly before and during laying and do not store calcium for egg formation. Many p asserines need to cat extraneous calcium in the form of snail shells or cal careous grit to acquire the element. However, very little is known about va riation in the dependency of birds on extraneous calcium, and where this ca lcium is acquired. Using reports from volunteers who provided extraneous ca lcium sources at feeder sites across North America we documented that (1) t he use of extraneous calcium varied during the breeding season; (2) the loc ation in which species preferentially took the calcium varied with typical feeding location, aside from swallows which, somewhat surprisingly, favored calcium offered on the ground; (3) Brown-headed Cowbirds (Molothrus ater) did not visit calcium sites more often than other blackbirds; (4) calcium u se varied among species with thrushes, wrens, and woodpeckers taking calciu m only rarely, and swallows, pigeons, and corvids taking calcium frequently . The most surprising result perhaps was the very high frequency of calcium use in jays; Blue Jays (Cyanocitta cristata) may hoard calcium in the fall .