Effects of isolation and mixing of social groups on heart rate and behaviour of red deer stags

The effects of visual and spatial isolation from other deer (Experiment 1), and of mixing with unfamiliar deer (Experiment 2) on the behaviour and heart rate of 16 yearling red deer stags were measured. In each experiment, the deer were initially confined in an indoor pen for 1 min in the presence of two handlers and two familiar stags (Stage I), then given two successive treatments for 1 min (Stages II and III). In Experiment 1, treatments in Stages II and III were confinement in isolation from deer and humans (Treatment IS), and confinement with the two familiar stags (Treatment GP). Eight deer received Treatment IS then Treatment GP and eight received Treatment GP then Treatment IS. Heart rate was higher during Treatment IS than Treatment GP, and deer made more steps, nosed and made head movements at the perimeters of the enclosure more frequently than during Treatment GP ( P < 0.05). In Experiment 2, treatments in Stages II and III were confinement in the presence of five familiar stags (Treatment F) and confinement in the presence of five unfamiliar stags (Treatment S; five yearling stags or five 2-year-old castrated stags). Heart rate was higher during Treatment S than Treatment F, and the deer stepped and nosed enclosure perimeters more during Treatment S. In addition, deer received or instigated aggressive interactions more frequently during Treatment S than Treatment F, and groomed themselves less ( P < 0.05). The increases in heart rate and changes in behaviour indicated that social isolation and mixing with unfamiliar deer were stress-ful to red deer. The responses to the acute social stimuli used in the study could be useful in identifying other social stressors experienced by deer during handling.