Time-of-day bias in diurnal raptors in arid region of Rajasthan

Activity patterns of raptors may vary through the day and influence their detectability which may further affect their abundance estimate. In this study, we exhibit the effect of time-of-day bias (survey time), in different seasons (summer vs winter) and landscape feature (cultivated land, wasteland, flooded vegetation, desert, human habitation, grassland, barren land) on the detection and abundance of diurnal raptors in the arid region of Rajasthan, India. We used 50 transects, using the roadside point count method between March 2019 and February 2020 and recorded 3927 observations of 35 species belonging to 14 sub-family. To evaluate the effect of predictive variables, i.e., time-of-day, season and landscape features on abundance estimate of each species of raptors, the Generalised Linear Model (GLM) was used. Chi-square test (χ2) was used to assess the relationship between each species abundance and the period of day. The effect of time-of-day bias on abundance estimate was significant in case of Red headed falcon (χ2 = 6.60, p < 0.001), Steppe eagle (χ2 = 7.89, p < 0.001), and Black wing kite (χ2 = 26.46, p < 0.001), while it was not significant for Shikra (χ2 = 0.306, p = 0.97), Long legged buzzard (χ2 = 0.42, p = 0.93) and Pallid harrier (χ2 = 0.115, p = 0.12). We did not observe any significant relationship between time-of-the day bias and abundance of raptors in different seasons and landscape features for any raptor species. Raptors showed variation in activity patterns with respect to the activity of their prey species and foraging strategies. The road count method for raptor surveys is widely used, but very few studies have undertaken and considered time-of-day bias in abundance estimate. This study can help bridge this gap and design a suitable method for survey raptors.