Influence of nest box design on occupancy and breeding success of predatory birds utilizing artificial nests in the Mongolian steppe.
We monitored 100 artificial nests of four different designs to examine the occupancy and breeding success of predatory birds in nest site limited, steppe habitat of central Mongolia. Three species, upland buzzard Buteo hemilasius, common raven Corvus corax and saker falcon Falco cherrug, occupied artificial nests in all years and their number increased over the five-year study period, when the number of breeding predatory birds rose from 0 to 64 pairs in our 324 km2 study area. The number of breeding pairs of saker falcons increased at a faster rate than ravens, reflecting their social dominance. Saker falcons and common ravens preferred to breed inside closed-box artificial nests with a roof, whereas upland buzzards preferred open-top nests. For saker falcons nest survival was higher in closed nests than open nests but there was no significant difference in laying date, clutch size and brood size in relation to nest design. This study demonstrates that whilst nest boxes can increase breeding populations in nest site limited habitats, nest design may also influence occupancy rates and breeding productivity of the species utilizing them. Careful consideration is needed in designing nests to maximize occupancy rates and productivity.