Could hair cortisol in free-ranging cattle be a proxy of wolf predation patterns?

Cortisol is a biomarker of grey wolf (Canis lupus) prey selection on wild ungulates. Throughout its range, wolves may prey on free-range livestock, leading to conflicts with humans. This can compromise wolf conservation through culling or poaching. We investigate whether glucocorticoid concentration could be a biomarker of individual prey selection by grey wolves that depredate on free-ranging cattle (Bos taurus). To achieve this, cortisol concentration in hair samples from live (n = 46) and wolf-preyed (n = 19) cattle was determined by enzyme-linked immunosorbent assays. The effects of intrinsic and extrinsic variables-namely age, sex and food availability-on hair cortisol concentration (HCC) were investigated through linear mixed models with farm as a random effect. The analysis revealed that, against our initial hypothesis, wolf-preyed cattle had significantly lower HCC than live cattle (P = 0.009). Additionally, HCC was lower in subadults than in adults (P = 0.002), and was negatively correlated with food availability in adults, but not in subadults (P = 0.003). These results suggest that predation risk does not necessarily equal long-term physiological stress. Alternatively, it may indicate that cattle chronically exposed to stressors (i.e. presenting higher HCC) may exhibit more effective anti-predatory behaviours. Additionally, food availability for cattle may influence wolf predation patterns, as cattle may expand their foraging area by exploring unfamiliar areas, thereby increasing the likelihood of predator encounters. Further research is required to understand the relationship between the multitude of stressors acting on free-range cattle and wolf prey selection, with the aim of assessing the risk of individual cattle and eventually managing predation risk and human-wolf conflict.