Sunning in extreme heat by the critically endangered hooded vulture: a strategy to fight ectoparasites?

At least 50 families of birds expose themselves to solar radiation, a behaviour known as sunning (Clayton et al. 2010). Yet, the functional significance of this common behaviour is poorly understood. Several hypotheses have been proposed to explain why birds sun themselves, including acquisition/dissipation of heat for thermoregulation, drying of wet plumage, feather maintenance, or parasite removal (Kennedy 1968, 1969; Simmons1986; Blem and Blem 1993). These functions are not mutually exclusive and their relative importance likely depends on ecological context and evolutionary history. Nevertheless, accumulating evidence suggests that sunning plays an important role in the control of external parasites (Bush and Clayton 2018).