Bat activity in the interior of Arabuko-Sokoke Forest and adjacent farmlands in Kenya

Abstract

Although the coastal forests in Kenya are highly threatened by human activities, limited bat research has been undertaken in them or the human-modified habitats around them. We investigated insectivorous bat activity in Arabuko-Sokoke Forest (ASF) and adjacent farmlands, in order to understand how each habitat was used by bats. Bat activity was sampled with Pettersson D240X ultrasound detectors at 69 stations in different vegetation types in ASF (Cynometra forest, Brachystegia woodland and mixed forest) and farmlands (mango, coconut and mixed plots). The detector was always tuned to 33 kHz, and bat passes were counted along 10-minute 400 m transects at the start of each sampling hour in each station. In each activity survey station, insectivorous bats were also captured in mist-nets in order to determine which of the detector targeted bats could be captured. A total of 14,727 bat passes were counted in both habitats, which included 10,552 in the farmlands and 4,175 in ASF. The largest numbers of insectivorous bats were captured in farmlands. The mean number of bat passes per night in farmlands (152.9 ± 13.2) was significantly higher than in ASF (60.5 ± 4.6) (df = 68, t =-8.671, P <0.05, N = 69). There was no significant difference in the sampled medians of bat passes in the three main vegetation types both in the interior of the forest and in farmlands. Bat activity was highest during the rainy season. Bat activity in both habitats peaked at 1900hr (i.e. just after sunset), sharply declined to the lowest level at midnight, and then maintained a gradual increase from two to five in the morning. Although the farmlands in the study area had completely lost the indigenous vegetation found in ASF, some bat species, probably those more adapted to humanized environments, were found to use these habitats for foraging. This emphasizes the need for more bat research in humanmodified ecosystems in Africa in order to understand these patterns and establish proper conservation guidelines.

Diversity of invertebrates in Arabuko-Sokoke Forest and adjacent farmland, Gede-Kilifi County, Kenya

“…The ASF is a legally protected area, characterised by indigenous vegetation typical of the east African coastal forests [10,17] , while the farmland habitat is completely disturbed and modified into an agricultural landscape. Because the two contrasting habitats had been shown to host various types of insectivorous bat species [9,10] , there was need to provide data on diversity and abundance of invertebrates, which are the primary food items eaten by these bats. The results of our study indicated that the farmland in the eastern part of ASF as well as the interior of ASF and had similar invertebrate abundance.…”

“…Nevertheless, many individuals of the order Dipterans, Lepidopteran, and Blattodea were more common in ASF than in the farmland. Therefore, though the interior of ASF has been shown to have low insectivorous bats abundance and activity than the farmland [9][10][11] , most of the invertebrate orders preyed by these bats were also common in the forest interior. This probably indicates that the farmland and the interior of ASF were suitable foraging habitats for the insectivorous bat species found in the two study sites.…”

“…The activity of invertebrate peaked after nightfall (1900 hrs), and gradually or sharply deteriorated to the lowest level at 2300 hr in both study sites. The activity of insectivorous bats in and around ASF has been shown to be highest immediately after dusk (1900 hrs~2000 hrs) and is lowest after midnight [9,11] ). This possibly, suggests that insectiverous bats in the study area, sychronize their foraging activity with the availbility and abundance of invertebrate prey.…”

“…This study investigated the diversity and abundance of invertebrates, which are preyed by insectivorous bats in ASF and the adjacent farmland. Insectivorous bats studies, previously conducted both in the interior of ASF and farmland (Table 1), had shown that the farmland had higher activity of insectivorous bats and individual bat captures than in the interior of ASF [9][10][11] . Therefore, we predicted that invertebrate would be more abundant in the farmland than in the interior of ASF.…”

“…Invertebrate sampling stations were established in the open areas of selected farms. The 12 invertebrate sampling stations each, in the farmland and in the interior of ASF, were established in the general areas, that had been previously been used to sample insectivorous bat species [9][10][11] . In addition, a number of bat roosts actively used by bats to roost, during invertebrate survey occurred in the sampling areas in the farmland [18] .…”