Nest Box Temperature and Hatching Success of American Kestrels Varies with Nest Box Orientation

We studied orientation-dependent differences in nest box microclimate and American Kestrel (Falco sparverius) reproductive parameters in Idaho, USA. Unoccupied nest boxes facing west were 0.6° C cooler than boxes that faced south or east and had 20% lower relative humidity levels than boxes facing all other cardinal directions. Clutches in occupied boxes that faced southwest had a proportionately lower chance of hatching success (12 of 21 nests were successful), defined as having at least one egg hatch, than boxes that faced northwest (9 of 9 nests) or southeast (9 of 12 nests). The possible link between orientation-dependent differences in microclimate and hatching success, and the question of whether American Kestrels may select for orientation adaptively requires further investigation.