Factors Influencing Bats Assemblage Structure and Activity Patterns in Arabuko-sokoke Forest and Adjacent Farmland, Gede, Malindi-kenya

Abstract

Many coastal forests in eastern Africa are highly threatened by human activities, which have reduced most of them into small fragments that are in continuous disturbance. Arabuko-Sokoke Forest (ASF) is the only remaining, biggest coastal forest in eastern Africa, which currently exist as an ‘island’ in the midst of human-dominated landscape. This study was undertaken in the interior of ASF and agricultural areas east of this forest, here referred to as ‘farmland’ mainly to investigate factors which influenced bats community structure and their activity in both habitats, as well as understand local people’s perceptions about bats. Bats composition and their flight activity were sampled with mist-nets. Insectivorous bat activity was investigated with Pettersson D240x ultrasound detector, always tuned to 33 kHz. Bat roosts were mapped and bats in them sampled. Insectivorous bats invertebrates prey abundance was sampled with solar powered lights (DP Light DP-6005A) traps, in 12 different stations each in ASF and farmland. Point-centred Quarter (PCQ) method was used to sample woody vegetation in ASF and in the farmland. A semi-structured questionnaire was used to investigate attitudes toward bats of 394 people living around ASF. A total of 25 bat species were recorded in both study sites; including 25 in the farmland and 19 in ASF. The ASF had higher bat diversity than farmland (H’, ASF: 1.48 ± 0.2, Farmland: 1.33 ± 0.1). However the farmland had higher bat species richness than ASF (Chao1, ASF: 19 [19-25], farmland: 24 [24-32] species [0.95% CI]). In total 5,217 individuals of bats were captured, 82.9% in farmland and 19.1% in ASF. Thirteen roosts occurred in the farmland and only one in ASF. The mean flight activity of individual bats captured in mist-netted (fruit and insectivorous bats combined) in each hour in the farmland was (425.3 ± 95.1, N=10), and in ASF (88.4 ± 11.2, N=10). There was a significant difference between the medians of captured bats per hour in both habitats (U=9.5: p <0.0025, Mann-Whitney U-Test). A total of 14,727 insectivorous bats echolocation calls (passes) were recorded, including 10,552 in the farmland and 4,175 in ASF. The mean number of bat passes in farmland was (152.9 ± 13.2), while in ASF was (60.5 ± 4.6). There was a significant difference in the activity of insectivorous bats in both study sites (df = 68, t = -8.671, P <0.05). A total of 6,557 individuals of insectivorous bats invertebrates prey were captured in both study sites: 52% in the farmland and 48% in ASF. The mean number of insectivorous bats invertebrates prey captured per night in the farmland was (260.5 ± 52.9, N=12), and in ASF (200.3 ± 36.4., N=12). There was no significant difference between the medians of insectivorous bats invertebrates prey captured in both study sites (U=61: p >0.544, Mann-Whitney U-Test). The mean Diameter at Breast Height (DBH) of trees were significantly larger in the farmland than in ASF (t (838) = 6.8934; P = 0.0001). The mean % understory vegetation thickness of ASF was (38.2 ± 1.9) and that of farmland was (5.8 ± 2.3). There was a significant difference in the % understory vegetation thickness in both study sites (df = 209, t = -16.634, P <0.05, N = 210). The farmland had many fruit trees (385) which produce large fruits eaten by frugivorous bats, as compared to indigenous fruit trees (166) in ASF producing small fruits. Three main factors explained the higher bat abundance, species richness and activity in the farmland than ASF. First, the farmland had many bat roosts (13), some hosting multiple species and in large numbers (one limestone cave had more than a million individual bats), than in ASF (one). Second, large concentration of cultivated fruit trees (mango, cashew nut and neem trees), in the farmland produced fruits which when ripe, attracted many fruit bats (3,397) in the farmland as compared to few fruit bats (733) captured in ASF. Third, the openness of understory and canopy habitat in farmland facilitated bat flight as compared to the thick interior of ASF, which constrained foraging as well as bats movement. For example, although both study sites had the same insectivorous bats invertebrate prey abundance, still large number of insectivorous bats occurred in the farmland (930) than in ASF (157). In addition, many individuals of Egyptian Slit-faced Bat (Nycteris thebaica) a clutter tolerant bat species were captured in the farmland (40) than inside ASF (14). The findings of this study underscore the importance of the farmland habitat around ASF for bats conservation, and the need for more research in agricultural landscapes, in order to understand their roles in bats conservation in Africa. Majority of respondents associated bats with evil and implicated them in destruction of farmer’s fruits. About one-third reported active killing of bats or destruction of their roosting places; and similar number did not see any benefits of bats to humans. The elderly and more educated people had more positive attitudes toward bats than others. Females showed more negative attitudes toward bats and more beliefs to myths about bats than males, while the males had more hostile behaviour toward bats than females. To address the prevailing negative attitudes about bats around ASF, there is need to intensify bat education awareness among youths and females.