Monitoring wombat activity

During a study of bare-nosed wombats at Thredbo Diggings in the Kosciuszko National Park, Graham Brown and Greg Young used radio-telemetry to monitor the wombats' activities. The researchers found that 'while they are in their burrow they often remain completely still for many hours but short periods of activity will occur from time to time'. It is a likely guess that during those long periods of stillness the wombats are sound asleep, and that the short periods of activity occur when they scratch, change their sleeping position or move to another chamber in the burrow.

As it sleeps the wombat's breathing rate slows from a fairly rapid 30 times a minute to about 14 times. Graham Brown's research has shown that the heart rate decreases rapidly when a wombat returns to its burrow, while its body temperature, which has increased by nearly 3°C during the time it was feeding and moving about, falls at a steady rate to about 34.7°C, its normal temperature, while it is resting in its burrow. This indicates that heat stored while the wombat is active on the surface is lost slowly while it is inactive, and it is thought that in this way the amount of energy used for regulating the wombat's body temperature is reduced.

All warm-blooded animals are able to keep their body temperature constant, and this normal body temperature is slightly above that of their usual surroundings. But in the wombat, this ability to regulate its body temperature decreases as the air temperature rises above 25°C, yet temperatures much higher than this are frequently found in many parts of the wombat's range in summer, when temperatures of 35°C and even 40°C are not uncommon. A wombat exposed to temperatures of 35°C will become very distressed, and it probably could not tolerate such high temperatures for very long. Measurements taken by Graham Brown of the air temperature in burrows in summer showed that the temperature in the burrows never exceeded 25°C and was usually lower. During a period of extremely hot weather I inserted a maximum/minimum thermometer into a major burrow at a distance of three metres from the entrance and left it in place for three consecutive days. During this time the shade air temperature rose above 39°C for several hours each day and reached a maximum of 41°C on the third day, but the maximum temperature reached in the burrow was only 26.5°C. Thus the wombat is able to stay cool and comfortable in the burrow, and it does not emerge until the air temperature falls to an acceptable level, which appears to be when the surface air temperature is close to the burrow temperature.

When in the late afternoon the wombat moves from the coolest, darkest part of the burrow to a chamber closer to the entrance, it is probably assessing the temperature to see when this is low enough for it to emerge. Even if it is cool enough, the wombat will not usually move out in bright daylight in summer, but will wait until dusk, although it may leave the burrow during the afternoon if the day is cool and overcast.

At the other end of the scale, the wombat often encounters extremely cold conditions. In the mountain forests and subalpine areas where the majority of bare-nosed wombats live, temperatures often fall to 0°C and below. Southerns may also encounter freezing temperatures during winter, but the burrow again provides protection against these extremes, as its air temperature seldom falls below 4°C. In any case, the wombat is well able to cope with these low temperatures, and it will often leave the burrow during winter afternoons, although Graham Brown's study showed that bare-nosed wombats spend less time above ground in winter - about five hours in winter compared with about eight hours in summer. He also found that wombats are less active while in their burrows in the winter than they are during the warmer months, indicating that wombats may expend less energy in winter. This would be an advantage, as it would offset the reduction in the amount of food available that may occur in winter when the grasses on which wombats feed grow more slowly, and it could be very important in an alpine and subalpine environment where there is often a deep snow cover.

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