Skeletal development at the time of fledging in house wrens

Abstract

We examined skeletal development at the time of first flight in House Wrens (Troglodytes aedon) as one step in assessing whether calcium availability limits nestling growth in this species. Young wrens begin flying with about 49 mg of calcium in their skeletons, 30% less calcium than is found in adult skeletons. Degree of calcification varies greatly from bone to bone at first flight which suggests that, during development, growing nestlings selectively allocate more calcium to certain skeletal components than to others. The coracoids, which directly resist contractions of the large flight muscles, are the most calcified bones in the fledgling body. Unexpectedly, long bones of the wing are not highly calcified at nest-leaving and are less calcified than leg bones. Strong leg bones may reflect the fact that young use legs extensively when competing for food within nests, and that legs probably bear the brunt of hard, awkward landings which young birds experience before flight is perfected.