Space use and activity of Boiga cyanea - A major songbird nest predator in a seasonal tropical forest in Thailand

Predator-prey interactions are fundamental drivers of population dynamics. Studying both predator and prey species simultaneously yields particularly useful insights into these complex interactions. Despite being significant, widespread avian nest predators, Southeast Asian snakes are rarely simultaneously studied in relation to avian prey. The Green Cat Snake Boiga cyanea is a primary nest predator, estimated to be responsible for 17-33% of forest songbird nest depredations in Northeast Thailand. We explored both diurnal and nocturnal movements of 14 (5 male, 9 female) adult B. cyanea with radio-telemetry for an average of 68 +/- 16 days per individual, between 21 October 2017 and 8 June 2019 in the dry evergreen forest of the Sakaerat Biosphere Reserve (SBR). We quantified horizontal movements (m) and area of space use (ha) and activity through motion variance (6m2) during the study period using dynamic Brownian Bridge Movement Models (dBBMMs) and reported our findings within the context of a simultaneously run avian nest monitoring study initiated in 2013 within the same forest. On average, adult B. cyanea moved 56.4 +/- 10.4 m/day and used areas of 9.4 +/- 3.4 ha, while their activity averaged 2.8 +/- 0.8 6m2. Males moved 51.4 m/day farther than females, and in general, adult B. cyanea moved 50.3 m/day farther during the avian nesting season than the avian non-nesting season. We refrain from inferring statistical differences with the dBBMM outputs between sexes and seasons within our sample because of the unequal samples and sampling effort during the study period. Only two individuals (one male and one female) were sufficiently radio-tracked across both seasons (the avian nesting and non-nesting seasons), and these two displayed a clear increase in their respective movements, space use and activity during the avian nesting season. This could suggest that movements, space use and activity likely differ between the avian nesting and non-nesting seasons for male and female B. cyanea, however it is only two individuals. All individuals were exclusively nocturnal, moving throughout the night, and often descending from higher diurnal refugia (> 2 m) to forage closer to the ground after sunset. Our openly available data may yield further insight when combined with other major avian nest predator species like the congeneric invasive Brown Tree Snake Boiga irregularis on the island of Guam.

Automated summary

Studying the diurnal and nocturnal movements of green cat snakes provided insights into differences in male and female behaviors, with males moving farther than females. Adult green cat snakes were found to move farther during the avian nesting season compared to the non-nesting season. However, statistical differences between sexes and seasons were inconclusive due to unequal samples.