Original investigationNo lunar phobia in insectivorous bats in Kenya
Introduction
Avoidance of moonlight is a strategy used by many nocturnal animals to reduce the risk of predation by visually oriented predators (Williams, 1936; Erkert, 1974; Tuttle and Ryan, 1982; Horning and Trillmich, 1999; Lang et al., 2005; Kronfeld-Schor et al., 2013). Bats might be expected to show such lunophobic behavior (Morrison, 1978), because they are subject to considerable predation pressure imposed by birds and other visually oriented predators at dusk or at night (Speakman, 1991; Hartley and Hustler, 1993; Mello et al., 2013; Mikula et al., 2016). However, studies on bats´ responses to moonlight have produced contradictory results. Bats seem to behave differently depending not only on their identity, but also on where they are and what they do, and the outcome also depends on the method used to measure activity in a given study (Lang et al., 2005; Appel et al., 2017).
Responses to moonlight generally seem to be weak or absent in bats of the temperate zone (Negraeff and Brigham, 1995; Hecker and Brigham, 1999; Karlsson et al., 2002; Hałat et al., 2018), but it may be more common in some tropical bat species, including vampires (Crespo et al., 1972), frugivores (e.g. Morrison, 1978; Singaravelan and Marimuthu, 2002; Mello et al., 2013) and fishing bats (Börk, 2006), although among tropical insectivores the response seems to differ considerably with species and situation (Appel et al., 2017). With respect to high-flying and open-air insectivorous bats, the evidence is ambiguous. For example, while Holland et al. (2011) found no response to moonlight in the Neotropical Molossus molossus, Meyer et al. (2004) did find such response in similar African species.
A meta-analysis of studies on lunophobic behavior (avoidance of moonlight) in bats (Saldaña-Vázquez and Munguía-Rosas, 2012) suggested that avoidance reactions to moonlight is common in bats and that moonlight overall has a negative effect on their activity. Lunar phobia occurs primarily in tropical species that feed in exposed locations such as over water and near the forest canopy, in situations of high visibility to predators on moonlit nights (Saldaña-Vázquez and Munguía-Rosas, 2012). However, with respect to the Tropics, most studies included in the meta-analysis considered Neotropical species, mostly frugivorous, the responses of which may differ markedly from those of African insectivores, for example.
To evaluate the generality of the findings cited above, we monitored the activity of some common insectivorous bats of Africa (“house bats” mostly of the genera Scotophilus and Scotoecus) with respect to moonlight and other environmental variables (habitat, time of the day and season) over three years (2014–2016). These species typically feed in open or semi-open places at or below canopy level (SM, RS, AZ, JR, unpublished observations in Kenya, Monadjem et al., 2010), in situations where they may be visible on moonlit nights, and, therefore, according to Saldaña-Vázquez and Munguía-Rosas (2012), would be expected to show lunar phobia. We monitored the bats using ultrasound detectors along walked transects, testing the principal hypothesis that bats´ activity was independent of moonlight.
Section snippets
Study area
The study was undertaken in and around Arabuko-Sokoke Forest in coastal Kenya (03°20′S, 39°50′E, Fig. 1). The forest is located 0–135 m a.s.l. and receives 600–1100 mm of rainfall annually, mostly during two main rain periods in November-December (short rains) and April-June (long rains) (Bennun and Njoroge, 1999; Muchiri et al., 2001). The dry season occurs in January-March (McWilliam, 1987). The forest consists of two major broadleaved vegetation types - “Brachystegia” and “Cynometra”
Results
The number of bat passes recorded per 10 min ranged from 0 to 260, but the distribution was strongly right-skewed, with the most frequent count being 1 or 2 passes, median 8.00 (±8.89 median absolute deviation) and inter-quartile range 3.00−16.00. In 5.8% of the counts (54/930) we recorded no passes at all. The 95% confidence model set, defined by summed Akaike´s model weights, included only three models (Table 1). The best supported model explaining variation in the number of bat passes
Discussion
Our results led us to conclude that the bats studied failed to manifest lunar phobia or any other reaction to the presence or the phase of the moon. Instead, as much as 64% of the observed variation in activity could be explained by factors related to season, time and habitat. This result seems to be at odds with a previous observation in tropical Africa, which indicated that open air bats avoided moonlight (Meyer et al., 2004). Likewise, our results do not conform with the prediction from the
Acknowledgements
Funding was received from the British Ecological Society (Ecologists in Africa grant 4632-5670). Bat detectors were donated by Pettersson Elektronik AB. We thank Paul Webala for help with identification of bats and bat calls at Arabuko-Sokoke, the Kenya Forest Service for permission to work inside the reserve and the farm owners and their families who allowed us to work in their farms at night. We also acknowledge Simon Kajengo Kega, our local guide in Gede, who helped us in our communication
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