A comparison of the breeding ecology of birds nesting in boxes and tree cavities

We compared laying date, nesting success, clutch size, and productivity of four bird species that nest in boxes and tree cavities to examine whether data from nest boxes are comparable with data from tree cavities. Western Bluebirds (Sialia mexicana) gained the most advantage from nesting in boxes. They initialed egg laying earlier, had higher nesting success, lower predation rates, and fledged marginally more young in boxes than in cavities but did not have larger clutches or hatch more eggs. Plain Titmice (Parus inornatus) nesting in boxes had marginally lower predation rates, hatched more eggs, and fledged more young. They did not have higher overall nesting success, nor did they initiate clutches significantly earlier in boxes. House Wrens (Troglodytes aedon) nesting in boxes laid larger clutches, hatched more eggs, and fledged more young and had marginally higher nesting success and lower predation rates. Ash-throated Flycatchers (Myiarchus cinerascens) experienced no apparent benefits from nesting in boxes versus cavities, No significant 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 nest-box studies of reproductive success, predation rates, and productivity of cavity-nesting birds. Given the different responses of these four species to nesting in boxes, the effects of the addition of nest boxes on community structure also should be considered.