Personality Differences: In Lean Times Red Deer With Dominant Personalities Pay A High Price

Saving energy is important for humans and animals alike when resources are limited. Scientists at the Research Institute of Wildlife Ecology of the University of Veterinary Medicine, Vienna, found out that although higher-ranked red deer gain privileged access to patches of food, they also have higher metabolic rates and thus use more energy. This can be a serious disadvantage in winter when red deer rely largely on their limited stored body fat to survive.

Energy budget adjustments

Energy is the currency of life, and a central topic of wildlife ecological research is to understand how animals regulate their energy budgets with respect to its limited supply in the environment. Chris Turbill and colleagues set out to test the hypothesis that high rank, i.e. social dominance might be associated with higher metabolic rate. They measured heart rate and body temperature (proxy indicators for metabolic rate) using minimally invasive rumen transmitters in a herd of female red deer (Cervus elaphus) during winter. Red deer have a highly hierarchical herd structure. Before the experiment, behavioral observations were used to determine the social status of individuals in the group. The animals were allowed to move freely in the approx. 45 hectare large natural enclosure of the Research Institute. Owing to the poor natural forage available over winter, the deer were also fed pellets at an automated feeding station, which enabled the researchers to periodically restrict food rations and test the physiological impact of dominance in situations of food scarcity.

Dominance is costly

Red deer must withstand a negative energy balance over the winter season and maintenance of their body mass is critical to survival and reproduction. In lean times red deer, and other northern ungulates, save energy by drastically reducing their metabolism over cold winter nights – an energy-saving mechanism scientists refer to as “hypometabolism“. Socially dominant animals, however, are less good at this. The experimental results found that dominant individuals do have faster heart rates and higher body temperatures during winter compared to subordinates. Consequently, dominant individuals suffered higher rates of body mass loss during periods of low food availability than subordinates. Because the normally disadvantaged lower-ranked individuals do better in keeping their head low, slowing down, and chilling out, they seem to withstand severe winter conditions better.

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