A novel method using hair for determining hormonal levels in wildlife

ormones influence behaviour, and are also influ-enced by behaviour. Monitoring their levels cantherefore provide insights into the mechanistic aspects ofbehaviour. In male mammals for example, elevated levelsof testosterone are associated with increased aggressionand dominance (Creel et al. 1993, 1997; Mazur & Booth1998) and in social mammals, levels of stress hormones(e.g. corticosterone, glucocorticoid and cortisol) areassociated with rank (Sapolsky 1985; Creel et al. 1996,1997). Research has associated hormone levels with dif-ferent behaviours such as sexual, reproductive, courtship,parental, aggressive and feeding behaviours. Comparativetools for hormonal analysis provide insights into evolu-tionary theories based on behavioural aspects, such asreproductive suppression and the ‘challenge hypothesis’(e.g. Creel et al. 1993). In field studies, hormones are usually extracted fromblood samples, or noninvasively from saliva, urine andfaeces (Creel et al. 1992; Cavigelli 1999; Hirschenhauseret al. 1999; von Engelhardt et al. 2000). Samples derivedfrom trapped or handled animals are problematicalbecause stress may alter blood and urine hormonal levels(Creel et al. 1992). Additional problems with bloodsamples are that they are not always available, theamount that can be taken at a given time is limited, andvarious safety and ethical issues exist. Furthermore, bloodand saliva must be transported cold or frozen, conditionsthat are sometimes difficult to obtain in the field (Yang etal. 1998). Urine and faeces samples are sometimes diffi-cult to obtain from free-ranging animals that cannot becontinuously observed, or from species that deposit incommon latrines.An alternative source for hormones may be found inhair, which can be collected noninvasively, and is alreadyused to extract DNA (Woodruff 1993; Morin et al. 1994),trace metals, naturally occurring compounds and drugs(Wheeler et al. 1998). Hair is safe, readily available, andeasy to store and transport. Hair sampling does notinvolve pain or possible infection, and the analysis isunaffected by the momentary stress of capture (Yang et al.1998). Hair analysis may allow one to monitor hormonalchanges over weeks or months (between moults; Maurelet al. 1986) by shaving off a patch of hair and resamplingthe newly grown hair. Hormonal hair analysis offersonly a long-term profile, however, and is not suitable formonitoring hourly or daily (short-term) fluctuations inhormonal levels. It provides the resolution needed forstudies of main behavioural trends, especially in stablehierarchical social systems. Hair has already been used todiagnose early pregnancy in cows by detection of proges-terone (Liu et al. 1988), to detect oestradiol and testoster-one in cattle (Gleixner & Meyer 1997) and anabolicsteroid and corticosteroid abuse in athletes (Bowers S Hold et al. 1999; Kintz et al. 1999; Cirimeleet al. 2000). In humans, the levels of steroid hormones inhair do not vary significantly between different regions ofthe scalp (Wheeler et al. 1998). Oestradiol, progesteroneand testosterone levels measured in healthy humanadults’ hair correlate significantly with the levelsmeasured in their serum (Yang et al. 1998). As an example of the utility of this method, we usedata from our long-term study on rock hyrax,