Abstract:
We report on acoustic surveys of insectivorous bats
conducted during seven months of the year using
ANABAT recordings in two habitats (macadamia orchards
and adjacent riparian bush) in a subtropical agroecosystem
in northern South Africa. We defined two
functional foraging groups of bats based on their echolocation
calls: (i) open-air foragers (family Molossidae)
having narrow-band, low-frequency, low duty cycle calls;
and (ii) clutter-edge foragers (families Miniopteridae and
Vespertilionidae), having broad-band, higher frequency,
low duty cycle calls. Bat activity (number of bat passes)
was not significantly influenced by habitat. Total bat
activity and activity of both functional groups varied
significantly between seasons, being highest in summer
and autumn (coinciding with annual peaks in numbers of
Twin spotted (Bathycoelia natalicola) and Green (Nezara spp)
Stinkbugs, order Heteroptera, family Pentatomidae, and
Macadamia Nut Borer moths, Cryptophlebia ombrodelta)
and lower in winter and spring. No significant effect of
moon phase was detected, either on total activity or
activity of the two functional groups. We postulate that the
significant pattern of seasonality of commuting and/or
foraging activity of bats in macadamia orchards (which is
more marked in open-air foragers) may be driven by the
seasonal abundance of pest insects such as stinkbugs and
Macadamia Nut Borer moths.
