Urohidrosis and tarsal color in Cathartes vultures (Aves: Cathartidae)

Heat-stressed New World vultures (Cathartidae) practice urohidrosis by excreting urate-rich urine on their tarsi and feet to decrease body temperature through evaporative cooling. Soft part colors are useful taxonomic characters in Cathartes, but dried urates obscure the color and pigmentation patterns of the tarsi and feet. I describe these characters in fresh specimens of Cathartes aura (Turkey Vulture), C. burrovianus (Lesser Yellow-headed Vulture), and C. melambrotus (Greater Yellow-headed Vulture) collected in Guyana. Species-specific differences in the melanic pigmentation of the tarsi and feet are revealed when urates are removed. The rosy-red intertarsal joints, which are normally unobscured by urates, may function in intraspecific signaling in all three species. The seasonality and geographic extent of urohidrosis in Cathartes are unknown.