Lying down as a means of reducing fly harassment in red deer (Cervus elaphus)

Summary Resting time in red deer (Cervus elaphus) was shown to be more than twice as long on days when harassment by head flies (Hydrotaea irritans) was considered severe compared with days when fly harassment was estimated as low. Avoidance reactions in the deer decreased as soon as the deer reclined and became stabilized at a level corresponding to approximately 50% of the initial response frequency. The present observations do not give any clear indications as to whether it is the head flies per se or climatic factors that are the primary cause of reduced locomotory behaviour in the deer. It is concluded, however, that due to a causal relationship between the appearance of flies and certain types of weather, and because lying down has a relieving effect, inactivity may be an important part of the strategy used by red deer to cope with head fly harassment.