Abstract:
Hipposideros speoris occurring across all bioclimatic zones is one of the most
widespread bat species in Sri Lanka. This study focused on ecological traits and body
morphometrics of three colonies of H. speoris from ecologically diverse locations
namely a cave in Yakkala (62.6 m asl), a mine in Kegalle (155.3 m asl) and an
abandoned building in Thanamalvila (91.29 m asl). The sites were selected to capture
variation in roost structure, light exposure, elevation and colony size. Observations
were conducted from August 2024 to April 2025. Bats were captured using both active
and passive methods to obtain morphometric measurements, while roost
environmental conditions were assessed. Light penetration was measured using a lux
meter, and roost structure documented via direct observation. Roosts differed in
structure and illumination. The Yakkala cave, with four natural openings allowed
minimal light penetration (0.2 lux) into deeper roosting sections. The Kegalla mine,
shared with R. rouxii, had a single main opening, and bats inhabited interior areas with
no light penetration. In Thanamalvila, the roost had one dark entrance, with bats
clustered beneath the ceiling. Estimated colony sizes were 50, 100 and 500 in Yakkala,
Thanamalvila and Kegalle respectively. To reduce potential variations arising from
age, sex or reproductive status, data were normalized prior to analysis. Significant
differences were noted in several morphometric measurements across the colonies
(One Way Anova, P<0.05). Traits showing significant variation included tibia length
(P=0.0001), length of hind foot and claws (P=0.00), length of the thumb (P=0.038),
and several metacarpal dimensions. Body size differed significantly, with Yakkala bats
(P=0.022) being larger, while the Kegalle bats exhibited disproportionately longer hind
feet and claws. In contrast, characters linked to echolocation, such as ear and nose leaf
dimensions remained stable among populations. This study highlights heterogeneity
across a widespread bat species, suggesting phenotypic plasticity that may facilitate
adaptation to local environments. The consistency of echolocation traits supports the
hypothesis that acoustic structures might be evolutionary preserved due to functional
constraints. Overall, the findings may provide insights into intra-specific variation and
the ecological influences, contributing to the understanding of cryptic diversity among
Sri Lankan micro chiropterans.
