Life history stage and extrinsic factors affect behavioural time allocation in plains zebras (Equus quagga) in the Serengeti ecosystem

Abstract

Time is a limited resource and how well it is allocated to competing behaviours can profoundly affect Darwinian fitness. Life history theory predicts that the amount of time allocated to vital behaviours will change with life history stage, resulting in trade-offs between competing behaviours. Moreover, a range of environmental factors can also affect activity budgets. We studied diurnal time allocation by migratory plains zebras (Equus quagga) in the Serengeti ecosystem, Tanzania, and investigated the effect of life history stage, social environment, habitat structure, and day time on time allocation to five behavioural categories (grazing, resting, vigilance, movement, other). We expected (1) increased vulnerability to predation and impeded predator detection to increase vigilance and decrease resting and grazing; (2) energetically costly life stages to increase grazing and decrease resting; and (3) increasing age in young to result in increased vigilance and grazing and decreased resting. Our findings revealed that in young zebras, resting decreased and grazing increased from the youngest to the oldest age class. Band stallions spent more time grazing and less time resting and moving than bachelors. Lactating mares devoted more time to grazing but less to resting and vigilance than other mares. Mares spent most time vigilant in the last third and stallions in the first third of the day. Adult zebras moved more, and mares were more vigilant in the woodland boundary than on short grass plains. Taken together, our study identifies intrinsic and extrinsic factors shaping time allocation decisions and trade-offs between competing behaviours in plains zebra. How well animals allocate their limited time to competing behaviours will affect their survival and reproduction. For example, energetically costly life history stages often require an increase in foraging whereas when predators threaten survival, more time should be allocated to vigilance. Increased investment of time in one behaviour requires decreased investment in another or other behaviours; thus, trade-offs in time are expected. Life history theory predicts substantial changes in the time allocated to vital behaviours between life stages. We investigated the effect of life history stage and environmental factors on the behavioural time budgets of migratory plains zebras in the Serengeti ecosystem. Our results showed that life history stage, juvenile age and environmental factors determine how time is invested in vital behaviours, and the behavioural trade-offs this entails.