A COMPARISON OF THE BREEDING ECOLOGY OF BIRDS NESTING IN BOXES AND TREE CAVITIES

We compared laying date, nesting success, clutch size, and productivit y of four bird species that nest in boxes and tree cavities to examine whether data from nest boxes are comparable with data from tree cavit ies. Western Bluebirds (Sialia mexicana) gained the most advantage fro m nesting in boxes. They initialed egg laying earlier, had higher nest ing success, lower predation rates, and fledged marginally more young in boxes than in cavities but did not have larger clutches or hatch mo re eggs. Plain Titmice (Parus inornatus) nesting in boxes had marginal ly lower predation rates, hatched more eggs, and fledged more young. T hey did not have higher overall nesting success, nor did they initiate clutches significantly earlier in boxes. House Wrens (Troglodytes aed on) nesting in boxes laid larger clutches, hatched more eggs, and fled ged more young and had marginally higher nesting success and lower pre dation rates. Ash-throated Flycatchers (Myiarchus cinerascens) experie nced no apparent benefits from nesting in boxes versus cavities, No si gnificant relationships were found between clutch size and bottom area or volume of cavities for any of these species. These results suggest that researchers should use caution when extrapolating results from n est-box studies of reproductive success, predation rates, and producti vity of cavity-nesting birds. Given the different responses of these f our species to nesting in boxes, the effects of the addition of nest b oxes on community structure also should be considered.