The Research Institute of Wildlife Ecology has long been investigating the question how wild animals, in particular large herbivores, deal with the drastically different living conditions that winter brings. In addition to a marked reduction in the availability and quality of food, energy requirements are expected to be higher in cold temperatures. In our initial studies on red deer (Cervus elaphus) we were however surprised to learn that in winter their metabolic activity is about half of what it is in summer. This is also reflected in their food requirements. The animals eat only half as much in winter as in summer, even if they are offered ample high quality food. In winter red deer use the fat reserves that they have accumulated during summer and live frugally. They achieve a lower energy consumption primarily by reducing their inner heat production and lowering their body temperature. Especially in cold nights the animals do not balance out heat losses to the cold environment, instead they tolerate a decline in their body temperature. Due to their large size and associated thermal inertia the temperature loss is hardly noticeable in the body core, but can be substantial in the limbs and outer parts of the body. Red deer are therefore capable of physiological responses that were previously known only from hibernating animals. We now know through the expansion of research to other species that reactions similar to hibernation are widespread in ungulates of the northern latitudes (e.g. capricorn, Przewalski´s horse, and chamois).
The exploration of these amazing seasonal reactions of native wild animals is only possible thanks to the advanced telemetry technology that we have developed at the research institute. The continuous measurement of detailed physiological values over long periods is accomplished without stress to the animals. We use the long-known fact that ruminants do not have problems with small foreign bodies in their rumen. At FIWI we therefore developed miniature transmitters that are introduced into the reticulum by swallowing. These transmitters detect heart rate, which is a good measure of metabolic intensity, and the core temperature of the animals. The rumen transmitter communicates with a device in the animal´s collar, which also stores all measured data. The system is now also being used on free-roaming wild animals and allows for the continuous measurement of pulse rate, body temperature, activity and GPS position over a period of up to two years.