Tasmanian Devil - Ecology and Behaviour

Ecology and Behaviour

The Tasmanian devil is a nocturnal and crepuscular hunter, spending the days in dense bush or in a hole. It has been speculated that nocturnalism may have been adopted to avoid predation by eagles and humans. Young devils are predominantly crepuscular. There is no evidence of torpor.

Young devils can climb trees, but this becomes more difficult as they grow larger. Devils can scale trees of trunk diameter larger than 40 cm (16 in), which tend to have no small side branches to hand onto, up to a height of around 2.5–3 m (8–10 ft). Devils that are yet to reach maturity can climb shrubs to a height of 4 metres (13.1 ft), and can climb a tree to 7 m (25 ft) if it is not vertical. Adult devils may eat young devils if they are very hungry, so this climbing behaviour may be an adaptation to allow young devils to escape. Devils can also swim and have been observed crossing rivers that are 50 metres (160 ft) in width, including icy cold waterways, apparently enthusiastically.

Tasmanian devils do not form packs, but rather spend most of their time alone once weaned. Classically considered as solitary animals, their social interactions were poorly understood. However, a field study published in 2009 shed some light on this. Tasmanian devils in Narawntapu National Park were fitted with proximity sensing radio collars which recorded their interactions with other devils over several months from February to June 2006. This revealed that all devils were part of a single huge contact network, characterised by male-female interactions during mating season, while female-female interactions were the most common at other times, although frequency and patterns of contact did not vary markedly between seasons. Previously thought to fight over food, males only rarely interacted with other males. Hence, all devils in a region are part of a single social network. They are considered to be non-territorial in general, but females are territorial around their dens. This allows a higher total mass of devils to occupy a given area than territorial animals, without conflict. Tasmanian devils instead occupy a home range. In a period of between two and four weeks, devils' home ranges are estimated to vary between 4 and 27 km2 (990 and 6,700 acres), with an average of 13 km2 (3,200 acres). The location and geometry of these areas depend on the distribution of food, particularly wallabies and pademelons nearby.

Devils use three or four dens regularly. Dens formerly owned by wombats are especially prized as maternity dens because of their security. Dense vegetation near creeks, thick grass tussocks, and caves are also used as dens. Adult devils use the same dens for life. It is believed that, as a secure den is highly prized, some may have been used for several centuries by generations of animals. Studies have suggested that food security is less important than den security, as habitat destruction that impacts the latter has had more effect on mortality rates. Young pups remain in one den with their mother, and other devils are mobile, changing dens every 1–3 days and travelling a mean distance of 8.6 kilometres (5.3 mi) every night. However, there are also reports that an upper bound can be 50 kilometres (31 mi) per night. They choose to travel through lowlands, saddles and along the banks of creeks, particularly preferring carved-out tracks and livestock paths and eschewing steep slopes and rocky terrain. The amount of movement is believed to be similar throughout the year, except for mothers who have given birth recently. The similarity in travel distances for males and females is unusual for sexually dimorphic, solitary carnivores. As a male needs more food, he will spend more time eating than travelling. Devils typically make circuits of their home range during their hunts. In areas near human habitation, they are known to steal clothes, blankets and pillows and take them for use in dens in wooden buildings.

While the dasyurids have similar diet and anatomy, differing body sizes affect thermoregulation and thus behaviour. In ambient temperatures between 5 and 30 °C (41 and 86 °F), the devil was able to maintain a body temperature between 37.4 and 38 °C (99 and 100 °F). When the temperature was raised to 40 °C (104 °F), and the humidity to 50%, the devil's body temperature spiked upwards by 2 °C (3.6 °F) within 60 minutes, but then steadily decreased back to the starting temperature after a further two hours, and remained there for two more hours. During the this time, the devil drank water and showed no visible signs of discomfort, leading scientists to believe that sweating and evaporative cooling is its primary means of heat dissipation. A later study found that devils pant but do not sweat to release heat. In contrast, many other marsupials were unable to keep their body temperatures down. As the smaller animals have to live in hotter and more arid conditions to which they are less well-adapted, they take up a nocturnal lifestyle and drop their body temperatures during the day, whereas the devil is active in the day and its body temperature varies by 1.8 °C (3.2 °F) from its minimum at night to the maximum in the middle of the day.

The standard metabolic rate of a Tasmanian devil is 141 kJ/kg (15.3 kcal/lb) per day, many times lower than smaller marsupials. A 5-kilogram (11 lb) devil uses 712 kilojoules (170 kcal) per day. The field metabolic rate is 407 kJ/kg (44.1 kcal/lb). Along with quolls, Tasmanian devils have a metabolic rate comparable to non-carnivorous marsupials of a similar size. This differs from placental carnivores, which have comparatively high basal metabolic rates. A study of devils showed a loss of weight from 7.9 to 7.1 kilograms (17 to 16 lb) from summer to winter, but in the same time, daily energy consumption increased from 2,591 to 2,890 kilojoules (619 to 690 kcal). This is equivalent to an increase in food consumption from 518 to 578 grams (18.3 to 20.4 oz). The diet is protein-based with 70% water content. For every 1 gram (0.035 oz) of insects consumed, 3.5 kilojoules (0.84 kcal) of energy are produced, while a corresponding amount of wallaby meat generated 5.0 kilojoules (1.2 kcal). In terms of its body mass, the devil eats only a quarter of the eastern quoll's intake, allowing it to survive longer during food shortages.

The devil is a keystone species in the ecosystem of Tasmania.