Vigilance adjustments in relation to long- and short term risk in wild fallow deer (Dama dama)

The risk allocation hypothesis predicts that vigilance should be adjusted to the temporal variation in risk. We test this hypothesis in wild fallow deer exposed to short term (disturbance) and long term (presence of a fawn after parturition) changes in risk. We recorded the proportion, frequency and type of vigilance and size of used area before and after parturition, in GPS-collared wild female fallow deer. Vigilance was divided in two main groups: “non-grazing vigilance” and “grazing vigilance”. The latter group was divided into “grazing vigilance while chewing” and a “grazing vigilance when chewing was interrupted”. By recording external disturbance in form of passing cars, we were able to investigate if this altered the amount, and type of vigilance. We found that females increased the proportion and frequency of “grazing vigilance stop chewing” after parturition. The “grazing vigilance chewing” was unaffected, but “non-grazing vigilance” decreased. Disturbance increased the proportion “grazing vigilance stop chewing” to the same extent before and after parturition. We found a clear decrease in female home range size after parturition as a possible behavioural adjustment. The increase in “grazing vigilance stop chewing” after parturition is a rarely described but expected cost of reproduction.