Where do the Tropical Owls Roost: Multiscale Habitat Variables Explain Roost Site Selection by Two Sympatric Otus Species in the Andaman Archipelago, India

Abstract

Understanding the niche differentiation between sympatric species that permit species to coexist and partition resource is the central concept in ecology. In this context, we evaluated the differences in roost site resources between two sympatric Otus species — Andaman Scops-owl Otus balli and Oriental Scops-owl Otus sunia in the Andaman Islands using a multi-scale approach. We measured variables that influence roost site use by owls at three different scales (tree, patch and macro). A total of 38 and 69 independent roost locations of O. balli and O. sunia respectively were recorded. We found that both species showed a high preference for Arecaceae plants at tree scale, possibly for their spiny structures that could offer protection. But both species showed different selection patterns at the patch and macro scales. At the patch scale, O. balli selected roosting sites in patches with relatively mature tree stands (characterised by higher tree height, girth at breast height and canopy cover) with thick understory cover (understory cover, height, and herbaceous elements). In contrast, O. sunia was found to select trees in secondary or highly disturbed forests. Land use and land cover types distinguish both species from their habitat preferences at a macro scale with a very low predicted overlap. The area of potential roost sites is very low for O. balli when compared to O. sunia. Our findings suggest that the two sympatric species' preferences for roost sites are shaped by the characteristics of evergreen forests of the Andaman Islands. Hence, any further changes to this forest type may have adverse effects on the endemic O. balli.