Bats and Wind Power

While bats have sophisticated means of detecting their environment and orienting themselves (echolocation or well-developed vision), bat fatalities have been found at wind turbines. This is because large turbine blades move too fast to allow bats to avoid collision: a 75m blade moving at 8 m/s near the nacelle will result in the blade tip reaching 117 m/s (or 423 km/hr). Furthermore, echolocating bats may not echolocate on known routes and so may be surprised by the appearance of new turbines in routine flight paths. Bats may also be killed at wind turbines due to Barotrauma (internal injuries due to decompression in the zone of low air pressure near moving blades; Baerwald et al., 2008).

Unprecedented numbers of bats are killed at wind energy facilities in North America (Baerwald & Barclay, 2009) and Europe (Rydell et al. 2012; Camina 2012; Georgiakakis et al. 2012; Lehnert et al. 2014; Eurobat 2015). There are few other well-documented threats to bat populations causing fatalities of such a magnitude (Cryan, 2011). It has been estimated that 650 104 – 1 308 378 bats have been killed across 73 Wind Energy Facilities in Canada and the U.S.A from 2000 - 2012 (Arnett and Baerwald, 2013). Other estimates indicate that, in 2012, approximately 600 000 (Hayes, 2013) to 888 000 (Smallwood, 2013) bats may have died as a result of interactions with wind turbines in the USA. In South Africa, bat fatalities at operational facilities have been reported by Doty and Martin (2012), Aronson et al. (2013) and MacEwan (2016) and are on a linear increase as more turbines are put into operation. Furthermore, the impacts of operation wind energy facilities in South Africa is greatly under-reported.

Bat fatalities may outnumber bird fatalities by 10:1 (Barclay et al. 2007) and fatality rates may be affected by turbine size (Barclay et al. 2007) and wind speed (low-wind nights associated with increased fatality; Arnett 2005; Arnett et al. 2008; Horn et al. 2008). Most documented impacts include fatality via direct collision (Rollins et al. 2012) and barotrauma (Baerwald et al. 2008), but there are other impacts. These include roost disturbances and/or destruction, destruction of foraging habitat, displacement of bats from their foraging habitat and the formation of a barrier to commuting or seasonal movements (migrating routes). Both migratory and non-migratory bats are vulnerable to impacts from wind turbines. Migrating bats fly at heights which may bring them into contact with wind turbines, and resident bat species that routinely fly at rotor-sweep height (such as those in the Family Molossidae (free-tailed bats)) are also at risk. Furthermore, the potential barrier effect of multiple wind energy facilities in an area presents a particular threat to migratory bat species.

Bats 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 only recover slowly (if at all) from declines. Until we have a better understanding of South African bat population levels and fluxes, bat ecology and migration, it is recommended that a precautionary approach is adopted when evaluating the potential impact of a wind energy facility on bats.