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 similar to 0.6 degrees C cooler than boxes that faced south or east and had similar to 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. Received 25 September 2008. Accepted 3 June 2009.