SKELETAL DEVELOPMENT AT THE TIME OF FLEDGING IN-HOUSE WRENS

We examined skeletal development at the time of first flight in House Wrens (Troglodytes aedon) as one step in assessing whether calcium ava ilability limits nestling growth in this species. Young wrens begin fl ying with about 49 mg of calcium in their skeletons, 30% less calcium than is found in adult skeletons. Degree of calcification varies great ly from bone to bone at first flight which suggests that, during devel opment. growing nestlings selectively allocate more calcium to certain skeletal components than to others. The coracoids, which directly res ist contractions of the large Eight muscles, are the most calcified bo nes in the fledgling body. Unexpectedly, long bones of the wing are no t highly calcified at nest-leaving and are less calcified than leg ban es. Strong leg bones may reflect the fact that young use legs extensiv ely when competing for food within nests, and that legs probably bear the brunt of hard, awkward landings which young birds experience befor e flight is perfected.