The daily activity period of the brown hare (Lepus europaeus)

The times of 241 entries into and 573 exits by brown hares from their forms on a 65 ha area of the Somerset Levels, South West England, were recorded over a ten year period to reveal the variation during the year of the duration of the daily activity period. In December when nightlength was 16 h, activity was exclusively nocturnal; intervals between entry and sunrise were Longer and less consistent than those between sunset and exit. In June with nightlength down to 7.4 h, activity was part diurnal, post-sunrise and pre-sunset, for a total of 6 h. From a peak duration of 14.5 h in December, the activity period declined to 12 h in the third week of March, mirroring night time duration. It then increased to 13.5 h in late midsummer before again reducing in the autumn. It is suggested that the proximate cause of this circannual cyclicity is an aversion to daylight activity.