Physiological response of a wild rodent to experimental manipulations in its natural environment using infrared thermography

Heat loss from non-insulating body parts of rodents can be used as a proxy to Stress-Induced Hyper-thermia (SIH) and can be detected via non-invasive methods, such as infrared thermography (IRT). Although IRT has been systematically used to detect SIH in captive or laboratory animals, very few studies have been performed in wild situations. We investigated the SIH in a wild rodent, the Eastern Broad-toothed Field Mouse Apodemus mystacinus, faced with novel stressors in its natural habitat, using IRT. We subjected live-trapped individuals to six consecutive experimental manip-ulations (Experimental Manipulations Phase -EMP), and then we temporarily transferred them to a wooden box to partly overcome the stressful challenges (Transitory Release Phase -TRP). We used the maximum eye temperature difference between the start of the EMP and the start of the TRP (& UDelta;TSIH) as the best estimate of SIH. Mean eye temperature during EMP differed significantly from that of TRP for each individual and the differences were similar when examined separately as to sex, trapping history, or breeding condition. Comparison of eye temperature time series for different trapping history groups showed a higher similarity of the response of first captures with 2nd and 3rd recaptures than of first captures with 1st recaptures, verified by a comparison of & UDelta;TSIH for these groups. Larger-sized first-captured individuals appeared less stressed by the experimental procedure than smaller-sized individuals. Overall, IRT appears to be a useful and feasible method for non-invasive monitoring of SIH.