Diurnal and ultradian rhythms of behaviour in a mare group of Przewalski horse (Equus ferus przewalskii), measured through one year under semi-reserve conditions

Investigations were conducted on four horses from a group of 12 Przewalski mares raised in different toes and kept in a 44-ha enclosure under semi-nat ural conditions. Activity and feeding were continuously measured every seco nd and were saved every 15 min by the storage-telemetry system ETHOSYS, fro m June 1995 to July 1996. Body mass of the horses was regularly recorded. D aily and monthly mean values, power spectra and DFC (as a measure for stabi lity of rhythms synchronised with circadiurnal period) for activity and fee ding were calculated. The general pattern of activity and feeding over the year was closely related to sunrise and sunset. Feeding accounted for 40% o f total activity in summer and 62% in spring (all-year average being 52%). The level of activity was lowest in winter; whereas feeding was lowest in s ummer. The time budget for feeding reflected both feeding conditions and th e annual pattern of body condition. Greatest activity occurred during dayli ght hours. Only on hot summer days, activity at night was higher than durin g daylight hours. Spectral analysis of activity and feeding in Przewalski h orse showed a time pattern which was characterised by 24-h rhythmicity, but also by ultradian components with period lengths between 4.8 and 12 h, i.e ., an activity pattern of up to five strong bouts per day. Annual variation in the pattern of power spectra was not high during the year. Results are discussed in connection with horse feeding strategy. Analysing the time str ucture of long-term and continuously measured activity and feeding could be a useful method to follow the general living conditions, especially the nu tritional situation and to detect stressful conditions. (C) 1999 Elsevier S cience B.V. All rights reserved.