A paucity of data exists with which to assess the effects of wind turbines noise on terrestrial wildlife, despite growing concern about the impact of infrasound from wind farms on human health and well-being. In 2013, we assessed whether the presence of turbines in Great Britain impacted the stress levels of badgers ( Meles meles ) in nearby setts. Hair cortisol levels were used to determine if the badgers were physiologically stressed. Hair of badgers living >1 km of a wind farm had a 264% higher cortisol level than badgers <10 km from a wind farm. This demonstrates that affected badgers suffer from enhanced hypothalamo-pituitary-adrenal activity and are physiologically stressed. No differences were found between the cortisol levels of badgers living near wind farms operational since 2009 and 2012, indicating that the animals do not become habituated to turbine disturbance. Cortisol levels in the affected badgers did not vary in relation to the distance from turbines within 1 km, wind farm annual power output, or number of turbines. We suggest that the higher cortisol levels in affected badgers is caused by the turbines' sound and that these high levels may affect badgers' immune systems, which could result in increased risk of infection and disease in the badger population.
Humans living within 2 km of a wind farm frequently report suffering from ill health (Shepherd et al. 2011), with symptoms ranging from headaches and sleep disturbance to increased stress (Pedersen 2009). Such symptoms are referred to as wind turbine syndrome (WTS; Colby et al. 2009), and it is widely attributed to audible or infrasound (sound with a frequency below 20 Hz; Salt and Kaltenbach 2011). Although the first UK public wind turbine became functional in 1951 (Price 2004), the effects of wind farms on human health remain poorly understood.
The impact of turbines on terrestrial wildlife is also not well understood. Research by Rabin et al. (2006) has demonstrated that wind turbines can have a negative impact on wildlife: squirrels living near turbines exhibit increased behavioral stress. Badgers (Meles meles) are suitable mammals to further assess physiologic changes as a result of wind farm developments because they often reside in habitats in which turbines are constructed. Importantly, badgers also have a similar hearing range to humans (Heptner 2002).
To ascertain if ‘‘affected’’ badgers show physiologic stress (hereafter referred to as stress), cortisol levels in badgers chronically exposed to turbine disturbance were compared with the cortisol level of badgers in comparable areas without turbines. Cortisol is a steroid hormone assembled from cholesterol in the adrenal gland (Werbin and Chaikoff 1961), and this pathway is controlled by the hypothalamus in response to stress (Lundberg 2005). This same relationship exists for lower vertebrates: Kikuchi (2010) reported that fish develop raised cortisol levels when subjected to conditions of an offshore wind farm reconstructed in the laboratory.
The function of cortisol is to increase the sugar level in the blood through gluconeogenesis and to redirect energy (Kirschbaun et al. 1997) toward parts of the body, such as the brain and muscles, which would help the individual escape an immediate threat. In turn, this starves the immune and reproductive systems and may hinder their vital function (Mostl and Palme 2002; Maeda and Tsukamura 2006). The effect of a short-term increase in cortisol is insignificant, but a prolonged increase in cortisol can lead to serious suppression of the immune system (Mostl and Palme 2002); in humans, it has been recorded to exacerbate an individual’s susceptibility to infection (Agarwal et al. 2002; Cohen et al. 2012). Chronic raised cortisol may also affect reproduction (Tilbrook et al. 2000; Mostl and Palme 2002), as demonstrated in meerkats, where elevated stress increases abortion rates (Young et al. 2006).
In mammals, cortisol levels are usually determined from blood, urine, saliva, or feces (Morton et al. 1995; Creel et al. 2002) but obtaining such samples from badgers poses significant problems of capture, restraint, and handling, all of which cause stress. Hair samples can be collected noninvasively, and cortisol from hair has been shown to give a reliable measure of chronic stress in animals, including wildlife (Davenport et al. 2006). The use of hair further avoids the problem of diurnal fluctuations of cortisol level in body fluids (Edwards et al. 2001), as it gives a measure of the average cortisol level over a prolonged period (Davenport et al. 2006). Assaying hair is further justified in that saliva and feces need to be fresh (Washburn and Millspaugh 2002; Descovich et al. 2012), which is challenging with wild animals in remote sites.