Footedness in merlins: Raptors perching in a cold climate.

ABSTRACTPerching or standing on one foot is commonly reported in birds but the level of consistency in using one foot over the other has been less-well documented in most species, particularly birds of prey. For birds experiencing colder temperatures, unipedal perching has been attributed to limiting heat loss through unfeathered legs and feet; individuals should spend longer periods of time perched on one foot as temperatures decrease. Using radio tracking, I collected 486 hours of observations on nine overwintering, free-living merlins (Falco columbarius) in Saskatoon, Canada. Five merlins displayed clear preferences to perch on one foot, however the direction of preference was not consistent and four birds were ambidextrous. There was a curvilinear response in the proportion of time spent in unipedal posture versus temperature, with a peak of ∼22% of the time at moderate temperatures (-10 to -19°C), but lower values at warmer and colder temperatures; the main effect of the squared term for temperature was highly influential while individual foot preference had no impact on the use of unipedal perching. Although preferential use of one foot for perching was displayed by some individuals, thermoregulation may not be the primary driver of this behaviour at colder temperatures.