Shifting incubation rhythms in response to predation risk and the length of the response in mountain bluebirds

Abstract Parent birds may alter incubation rhythms in response to predation risk but few studies have examined the recovery time immediately after exposure to a predator. Here, we examined incubation rhythms in mountain bluebirds ( Sialia currucoides ) in response to a simulated nest predator, a taxidermy-mounted squirrel. We used data loggers (iButtons) to measure the recess (off-bout) length, recess rate, and constancy of incubation and found no relationship between incubation rhythms and female age, body size and aggressiveness. Incubating females reacted to the predator by reducing nest visitation rates and increasing recess length but did not change incubation constancy. Instead, constancy was negatively associated with ambient temperature. Changes in incubation behaviour lasted about 48 h before returning to pre-exposure patterns. Our results suggest that modifying incubation rhythms is costly for female birds and the demand to regulate egg temperature efficiently limits the length of behavioural responses to the threat of nest predation.