Abstract
Cave roosting bats represent an important component of Southeast Asian bat diversity and are vulnerable to human disturbance during critical reproductive periods (pregnancy, lactation and weaning). Because dramatic growth of cave tourism in recent decades has raised concerns about impacts on cave bats in the region, we assessed the reproductive phenology of two insectivorous species (Hipposideros larvatus sensu lato and Taphozous melanopogon) at three caves in Cambodia for 23 months in 2014–2016 and evaluated human visitation to these sites between 2007 and 2014. Despite the differing foraging strategies employed by the two taxa, the temporal consistency observed in proportions of pregnant, lactating and juvenile bats indicates that their major birth peaks coincide with the time of greatest cave visitation annually, particularly for domestic visitors and namely during the Cambodian new year in April. They also reflect rainfall patterns and correspond with the reproductive phenology of insectivorous cave bats in Vietnam. These findings were predictable because 1) insect biomass and thus food availability for insectivorous bats are optimal for ensuring survival of young following this period, and 2) the Khmer new year is the most significant month for religious ceremonies and thus domestic cave visitation nationally, due to the abundance of Buddhist shrines and temples in Cambodian caves. While the impact of visitor disturbance on bat population recruitment cannot be empirically assessed due to lack of historical data, it is nonetheless likely to have been considerable and raises a conservation concern. Further, because growing evidence suggests that insectivorous cave bats exhibit reproductive synchrony across continental Southeast Asia where countless cave shrines are heavily frequented during April in Theravada Buddhist countries (e.g., Myanmar, Thailand, Cambodia and Laos), our results may have wider applicability in the region. We consequently advocate for increased emphasis on sustainable cave management practices in Cambodia and further investigations to determine whether our findings present a broader concern for cave bat conservation in Southeast Asia.
Highlights
Bat populations take a relatively long time to recover from declines associated with humans due to their low annual reproductive rates [1]
Both species were captured every sampling month with a monthly mean of 28 bats (SD ±18.57) for H. larvatus s.l. and 14 bats (SD ±8.97) for T. melanopogon, captures of both species were noticeably greater in the first study year compared to the second (H. larvatus s.l.: 388 vs. 252 bats, T. melanopogon: 208 vs. 107 bats)
The reproductive pattern of H. larvatus s.l. in southern Cambodia may be classified as extended seasonal monoestry
Summary
Bat populations take a relatively long time to recover from declines associated with humans due to their low annual reproductive rates [1]. Large numbers of cave bats are often concentrated into only a few specific roost sites resulting in high potential for disturbance [4] which is exacerbated by their high roost fidelity [5]. Development of caves for tourism typically involves the introduction of artificial lighting and physical alterations to the cave environment and alongside disturbance caused by their presence, cave visitors create significant fluctuations in temperature, relative humidity and carbon dioxide concentrations, all of which can lead to roost abandonment [6]. In a review of 225 subterranean sites in China for instance, it was found that recreational activities had pronounced detrimental effects on numbers of bat species and presence of species of special conservation concern [7]. Other studies have raised concerns about the impact of cave tourism on Chinese and Vietnamese bats [8,9,10]
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