Sex-based differences, diurnal and seasonal trends in thermoregulatory behaviour of nesting Painted Stork (Mycteria leucocephala)

To cope with heat stress, storks wet their legs by excreting on them, known as urohidrosis, and perform wing-spreading in which the wings are half extended in the form of an inverted triangle. While several studies have highlighted the role of urohidrosis as an important cooling mechanism and suggested a possible thermoregulatory function of wing-spreading, sex-based comparisons and trends of these behaviours throughout the breeding season remain unexplored. Here we explore thermoregulation in a wild population of Painted Storks (Mycteria leucocephala) nesting in the National Zoological Park, Delhi, India, through the non-invasive videography technique. Temperature, humidity and wind speed significantly influenced both urohidrosis and wing-spreading behaviours. Male storks exhibited higher rates of urohidrosis and spend more time wing-spreading compared to females. Seasonal and diurnal differences were observed with more urohidrosis and wing-spreading during the hottest hours of the day and early part of the nesting season in August-September. The rate of both behaviours declined as the nesting season progressed till November when ambient temperatures dropped.