Behavioral and Physiological Responses of Trap-Induced Stress in European Badgers

Abstract

Reasons for mammal trapping include removal of individuals for population management purposes, scientific purposes, pest control, and obtaining fur, skin, or meat for economic purposes. The type of trap used highly affects the responses of captured animals (Kreeger et al. 1990a, White et al. 1991). Research on captured red foxes (Vulpes vulpes) has shown that foothold traps inflict greater trauma compared with box traps even when the traps had padded jaws (i.e., the animal does not experience any obvious physical damage, Kreeger et al. 1990a). Also procedures, such as chemical immobilization, have been shown to affect the life history of mountain goats (Oreamnos americanus; Cote et al. 1998), moose (Alces alces; Ballard and Tobey 1981), and polar bears (Ursus maritimus; Ramsay and Stirling 1986). Thus, not only can entrapment cause physical trauma, such as limb, tissue, or tooth damage, but the overall response is likely to be affected by how the animal perceives the situation. White et al. (1991) demonstrated higher pathological responses in red foxes captured in box traps compared with untrapped individuals, which shows that even traps like box or cage traps that are likely to minimize physical injuries can have negative effects on animals. Stress-induced hyperthermia has been shown to be closely associated with activation of the hypothalamic-pituitary-adrenal axis and the sympathetic-adrenalmedullary system, for example, in foxes (Moe 1996), thus, resulting in increased heart rate, body temperature, and cortisol levels. Cortisol levels have been used as indicators of stress during restraint of wildlife species (Morton et al. 1995), but although physiological responses often can be useful indicators of stress (Broom and Johnson 1993), it is not suitable to use them alone as stress indicators (Rushen 1991) because similar reactions can also be observed during nonstress situations (Kreeger et al. 1989, 1990b). It is well-known that psychological factors may cause or increase stress responses in animals. If an individual is in a threatening environment and is not able to cope with the situation it is likely to be stressed even without any physical injury (Jensen and Toates 1993, Toates 1995, Jensen 1996). An animal’s ability to predict or control its situation highly influences the response, with stress levels decreasing with increased ability to predict or control the situation (Weiss 1972, Jensen 1996). Therefore, besides potential physical trauma, a captured animal might also be exposed to psychological stress by experiencing lack of control because it is unable to escape from the trap. Furthermore, during long entrapment times there is also a risk of enhanced stress levels due to disruption of, or failure to perform, natural behaviors such as feeding. External factors, such as type of trap, entrapment duration, and time of day, most likely affect the stress response. Also species-specific factors, such as diurnal rhythms, general activity levels, and sociality, are likely to have an influence on how the animal responds to the situation. The European badger (Meles meles) is a nocturnal species that lives in social groups varying in size from 2–30 individuals (Rogers et al. 1997). A group uses a shared territory with one or several setts, but the individuals commonly feed independently from each other (Kruuk 1978a). Badgers are used in Sweden to train earth dogs (i.e., dogs that enter the sett when hunting [e.g., foxes and badgers]), and our study was a part of a project investigating stress coping in such badgers on commission of the Swedish Ministry of Agriculture, Food, and Consumer Affairs. Our aim was to examine some behavioral and physiological (heart rate, body temperature, and fecal cortisol) responses of semitame European badgers to restraint in cage traps for short and long capture periods during day and night time. We also studied behavior during 3 consecutive nights postrestraint (i.e., after the treatment period) and compared behavior to undisturbed conditions. We predicted that longer entrapment would affect the badgers more than short entrapment periods in terms of higher heart rate, body temperature, and fecal cortisol metabolites (FCM) levels and in terms of more long-term changes in behavior. We also predicted that entrapment during dark hours when badgers normally are active would be more stressful than during daylight.