A true desert falcon with a delayed onset of heat dissipation behaviour

Abstract The Grey Falcon (Falco hypoleucos) is a rare Australian endemic bird of prey confined for its entire life to the continent's hot arid and semi-arid zone. The prevention of hyperthermia is therefore a crucial challenge. Birds, in general, rely on a dynamic balance between physiological mechanisms and the behaviours that augment them. Effective heat dissipation behaviours in birds include panting, airing and shade-seeking. These behaviours are readily observable in the field. We observed Grey Falcons, Peregrine Falcons (F. p. peregrinus and F. p. macropus) and Saker Falcons (F. cherrug) in the wild (from continuous webcam video for the latter two species) and compared their heat dissipation behaviours in relation to air temperature, exposure to direct solar radiation, wind speed, and relative humidity. Our results show that the desert-living Grey Falcon has a considerably higher heat dissipation behaviour threshold than the two non-desert Falco species. We show that this leads to the prediction that Grey Falcons should have reduced average activity levels in key aspects of their lives, throughout the year, relative to their congeners.