The Importance of Nest Box Placement for Barn Owls (Tyto alba)

SIMPLE SUMMARY: Nest sites for cavity-breeding birds are limited in many habitats such as in agriculture. Nest boxes are artificial nest sites that are added to provide birds a place to breed in areas where natural nest sites are lacking. For example, nest boxes are used to increase barn owl numbers in agricultural areas to reduce rodent damage in farmlands. Although nest boxes are added in different locations such as on poles and trees and in sunlight/shade, it is still unknown which location is better. Here, we compared the occupation of nest boxes by barn owls on trees, nest boxes on poles in the shade, and on poles in the sun. We found that more nest boxes were occupied when they were located on trees, followed by nest boxes on poles in the shade and nest boxes on poles in the sun. The number of nestlings raised in the nest boxes varied seasonally, with more being fledged early in the season in nest boxes located on poles in the sun whereas more nestlings were fledged later in the season in nest boxes located on trees. The seasonal difference is most likely due to the lower internal temperatures in nest boxes located on trees than in nest boxes on poles in the sun. Depending on the climate, it is important to consider variation in temperatures when adding nest boxes. ABSTRACT: Nest boxes have been used for years to increase breeding bird numbers for conservation and also in biological pest control projects. Barn owls (Tyto alba) have been used as biological pest control agents for rodents for years, and since nest boxes are costly for growers there is a need to determine whether nest box placement can increase the occupation of nest boxes and breeding success. We studied whether barn owl breeding in agricultural areas varied in nest boxes located on trees, poles located in the shade, and poles in the sun. The occupation of nest boxes was highest in nest boxes located on trees, followed by poles in the shade, and finally poles in the sun. In comparison, the number of fledglings was highest for nest boxes on poles in the sun followed by poles in the shade in the first half of the breeding season, whereas more nestlings were fledged in nest boxes on trees in the second part of the breeding season, which is most likely due to the higher internal temperatures in the nest boxes located in the sun. Interestingly, all the nest boxes’ internal temperatures were lower than the ambient temperatures but were much lower on trees than those on poles, most likely due to the trees providing better protection from the heat. It is therefore important to not only consider the placement of nest boxes, but how occupation and breeding success may vary seasonally.