Hooo-Hooo Volume 11 Nr 1 - Page 24

WildLife Group of the SAVA hypothalamic-pituitary-adrenal axis that leads to the release of glucocorticoids, and (2) the modulation of the autonomic nervous system that involves a decrease of the parasympathetic- and an increase of the sympathetic tone (Boonstra, 2004). To date, the primarily used indicator for stress in wildlife and zoo animal research are glucocorticoid levels. There are a number of sources from which glucocorticoids can be measured such as blood, saliva, faeces, urine, or integumentary structures; but each of these sources carries with it a number of caveats (Möstl and Palme, 2002; Sheriff et al., 2011; Dantzer et al., 2014). For instance, individual and sex-specific variation, storage conditions and uneven distribution of metabolites affect final results when measuring glucocorticoids from faeces (Hadinger et al., 2015). In human medicine and farm and companion-animal research, heart rate variability (HRV) has been used increasingly over the past decades to evaluate physical and psychological stress (Cardiology, 1996; von Borell et al., 2007). Analysis of HRV investigates the functioning of the autonomic nervous system of an individual. In a healthy heart, both branches of the autonomic nervous system are tonically active with a dominance of the vagal tone (von Borell et al., 2007; Porges, 2007; Pumprla et al., 2002. This activity creates irregular time intervals between consecutive heart beats. Measuring HRV quantifies these time intervals and, thus provides information about the balance between sympathetic and parasympathetic activity (Cardiology, 1996; von Borell et al., 2007) -- a high HRV indicates higher capacity of an individual to cope with environmental demands, whereas a low HRV is an indicator for stress (von Borell et al.; 2007, Thayer and Sternberg, 2006). HRV is a new approach in wildlife research to investigate stress, and only few previous studies have applied it. For example, HRV has been applied in brown bears to identify the drivers of hibernation (Evans et al., 2016) and to assess stress associated with human activity (Støen et al., 2015). In European roe deer, HRV has been applied to investigate seasonal changes (Theil et al., 2004) and to analyse stress control during physical 24 capture (Mentaberre et al., 2010). In a recent project, we applied HRV in free-ranging Przewalski’s horses to assess seasonal stress. With a self-constructed telemetry system consisting of an implanted transmitter and a storage unit located on a collar, we were able to obtain valuable data (including cardiac activity and other physiological parameters) over an extended period of time without disturbing the horses. Heart rate and HRV varied throughout the year, with lower values during the winter than during the summer. In spring, heart rate peaked along with a drop in HRV indicating increased allostatic load. In summary, we found that HRV is a probate method to study undisturbed reactions of wild animals to their changing environment over the long term. As current wildlife research focuses on the placement of the whole organism in its natural setting, biologgers are used more and more. Thus, when collecting physiological data, we recommend to measure heart rate on a beat-to-beat basis to allow the assessment of HRV. The combined measurement of HRV as a stress parameter and heart rate as an indicator for energy expenditure enables the valuation of allostatic load and facilitates the determination of an individual’s regulatory range and adaptive capacity. HRV represents a promising tool to understand how animals integrate their life cycles in an ever-changing environment and to identify the aspects of human influence that cause stress. References Boonstra R.2004.Coping with changing northern environments: the role of the stress axis in birds and mammals. Int. Comp. Biol. 44: 95-108. CARDIOLOGY, T.F.O.T.E.S.O. 1996. Heart rate variability standards of measurement, physiological interpretation, and clinical use. Eur. Heart J. 17: 354-381. Dantzer B, Fletcher QE, Boonstra R, Sheriff MJ. 2014. Measures of physiological stress: a transparent or opaque window into the status, management and conservation of species? Cons. Physiol. 2: cou023. Evans A, Singh N, Friebe A, Arnemo JM, Laske T, Fröbert O, Swenson JE, Blanc S. 2016. Drivers of hibernation in the