Three-dimensional stratification pattern in an old-growth lowland forest: how does height in canopy and season influence temperate bat activity?

The study of animal-habitat interactions is of primary importance for the
formulation of conservation recommendations. Flying, gliding and climbing
animals have the ability to exploit their habitat in a three-dimensional
way and the vertical canopy structure in forests plays an essential role
for habitat suitability. Forest bats as flying mammals may seasonally
shift their microhabitat use due to differing energy demands or changing
prey availability, but the patterns are not well understood. We
investigated three-dimensional and seasonal habitat use by insectivorous
bats in a temperate lowland old-growth forest, the Belovezhskaya Pushcha
in Belarus. We acoustically sampled broadleaved and mixed coniferous plots
in the forest interior and in gaps in three heights during two
reproductive periods (pregnancy/lactation versus post-lactation). In
canopy gaps, vertical stratification in bat activity was less pronounced
than in the forest interior. Vertical activity patterns differed among
species. The upper canopy levels were important foraging habitats for the
open-space forager guild and for some edge-space foragers like the
Barbastelle bat Barbastella barbastellus and the soprano pipistrelle
Pipistrellus pygmaeus. Myotis species had highest activity levels near the
ground in forest gaps. Moreover, we found species-dependent seasonal
microhabitat shifts. Generally, all species and species groups considered
except Myotis species showed higher activity levels during post-lactation.
Myotis species tended towards higher activity in the forest interior
during post-lactation. P. pygmaeus switched from high activity levels in
the upper canopy during pregnancy and lactation to high activity levels
near the ground during post-lactation. We conclude that a full
comprehension of forest bat habitat use is only possible when height in
canopy and seasonal patterns are considered.