Seasonal patterns of habitat use by insectivorous bats in a subtropical African agro-ecosystem dominated by macadamia orchards

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.