Effects of time and weather condition on Crested Serpent Eagle sightings along roads

Abstract

We conducted road-based censuses of the Crested Serpent Eagle Spilornis cheela perplexus on Iriomote Island, southern Japan, and analyzed sightings in relation to the time of day and weather conditions. Eagle numbers were highest in the morning, followed by the evening. Wind speed was negatively correlated with the number of individuals counted during both periods, but there was no relationship with humidity or temperature. As wind speed increased, the posture of perching eagles changes significantly with a greater tendency towards a forward-leaning posture. As the diet of Crested Serpent Eagle consists primarily of nocturnal amphibians and reptiles, food availability is likely increased in the morning and evening. However, windy conditions may incur an increase in energy expenditure for a sit-and-wait predator, consequently resulting in a negative effect on sightings. This study highlights the importance of considering the time and wind speed when analyzing road census results for this species.