Environmental Importance of Bats
Bats (Order Chiroptera) are long-lived mammals and females often produce only one pup per year, resulting in a life-strategy characterized by slow reproduction (Barclay and Harder 2003). Because of this, bat populations are sensitive to changes in fatality rates and their populations may only recover slowly from declines. Bats also act as potential indicators of environment health (Jones et al. 2009; Park 2015). Bats provide important ecosystem services (Cleveland et al. 2006; Kunz et al. 2011; Boyles et al. 2011; 2013; Lopéz-Hoffman et al. 2014; Maas et al. 2015). The relative value of bats may be greater in developing countries than in more developed regions, because even though the economic value of crops produced in developing countries is considerably less, their marginal value as food can be much greater (Boyles et al. 2013). Bats are major pollinators of fruiting trees, dispersers of seeds and controllers of insect populations, including those of agricultural pests. They have contributed substantially to medical research, to our understanding of radar and sonar and their droppings are highly prized in some parts of the world as fertiliser. A single small North American Little brown bat (Myotis lucifugus) can consume up to 1,200 small insects in an hour, almost 5,000 mosquito-sized insects a night per bat (Taylor 2000). A small colony of bats can therefore, consume over 200,000 insects in one night. In Sacramento USA, it was reported that the presence of sufficient numbers of bats due to proximity to a bat roost reduced fruit crop damage to pears by corn ear moth, by 55% (Long et al. 1998). Exclusion of bats and birds from Indonesian cacao plants resulted in a 31% decrease in cacao production due to increased insect damage (Maas and Tscharntke 2013). The estimated value of bats to the United States agricultural industry is approximately $22.9 billion/year and that the loss of bats in North America (due in part to wind turbines and white nose-syndrome) may lead to agricultural losses estimated at more than $3.7 billion/year (Boyles et al. 2011). In south western United States, the pest control value of bats to cotton was approximately $12 million per year between 1990 and 2008, amounting to between 6 and 28% of the total value of the crop (Lopéz-Hoffman et al. 2014). In the USA wind operators have also been fined $2.5 million as compensation for the impact on local biodiversity (Cuff 2010). Maine and Boyles (2015) have shown that bats are worth over $1 billion to the global corn industry.
In Africa, as in other parts of the world, bats provide essential ‘ecosystem services’. Insectivorous bats provide essential services through maintaining a healthy ecological balance by means of natural insect control. For example, in sugar cane monocultures in Swaziland, two species of molossid bats selectively foraged over sugar cane fields rather than over natural vegetation (Noer et al. 2012). In the same area, based on next-generation DNA sequencing from faecal pellets, several local pest insect species (including the borer moth, Eldana saccharina) featured in the diet of these species (Bohmann et al. 2011). Based on next-generation DNA sequencing results, five out of six bat species tested in macadamia orchards in a Limpopo study contained DNA from the major pest of macadamia, green vegetable stinkbugs (Nezara viridula) (Taylor et al. 2013a). Seasonal activity of bats foraging in these same macadamia orchards was correlated with the annual cycle of two stinkbug pest species (Taylor et al. 2013b). Stinkbugs of the Family Pentatomidae result in damage of up to R50 million per year in South African macadamia and avocado orchards (Schoeman 2013). Bats also play an important role in social health by combatting disease (e.g. malaria; Gonsalves et al. 2013). Frugivorous bats provide seed dispersal (thus aiding forest regeneration) and pollination services. In a recent study at Amani in Tanzania, fruit bats were shown to disperse 20% of the local submontane forest trees for hundreds of metres (Seltzer et al. 2013). Unlike in South America where bats seem important in dispersing pioneer species in regenerating forests, fruit bats in Africa appear to play an important role in propagation of larger forest trees including species economically important for timber production (Muscarella and Fleming, 2007).
The potential loss of these ecosystem services should be considered when assessing the environmental impact of wind energy facilities. The possible loss of bat colonies could potentially result in increased costs in pesticides and reduced agricultural productivity.
More information on the importance of bats to the environment can be found in the SABAA Pre-Construction Guidelines.