Short-beaked Echidna - Ecology and Behaviour

Ecology and Behaviour

No systematic study of the ecology of the short-beaked echidna has been published, but studies of several aspects of their ecological behaviour have been conducted. They live alone, and, apart from the burrow created for rearing young, they have no fixed shelter or nest site. They do not have a home territory they defend against other echidnas, but range over a wide area. The range area has been observed to be between 21 and 93 ha, although one study in Kangaroo Island found the animals there covered an area between 9 and 192 ha. Overall, the mean range areas across the various regions of Australia were 40–60 ha. There was no correlation between gender and range area, but a weak one with size. Echidnas can share home ranges without incident, and sometimes share shelter sites if not enough are available for or each animal to have one individually.

Short-beaked echidnas are typically active in the daytime, though they are ill-equipped to deal with heat because they have no sweat glands and do not pant. Therefore, in warm weather, they change their patterns of activity, becoming crepuscular or nocturnal. Body temperatures above 34°C (93°F) are believed to be fatal, and in addition to avoiding heat, the animal adjusts its circulation to maintain a sustainable temperature by moving blood to and from the skin to increase or lower heat loss. In areas where water is present, they can also swim to keep their body temperatures low. The "thermoneutral zone" for the environment is around 25°C (77°F), at which point metabolism needed to maintain body temperature is minimized. Echidnas can tolerate cold temperatures, and they hibernate during the winter both in cold regions and in regions with more temperate climates. The echidna is endothermic, and can maintain body temperatures of around 32°C. It can also reduce its metabolism and heart rate and body temperature. In addition to brief and light bouts of torpor throughout the year, the echidna enters periods during winter when it hibernates. During periods of hibernation, the body temperature drops to as low as 4°C (39°F). The heart rate falls to four to seven beats per minute—down from 50–68 at rest&mdash, and the echidna can breathe as infrequently as once every three minutes, 80 to 90% slower than when it is active. Metabolism can drop to one-eighth of the normal rate. Echidnas begin to prepare for the hibernation phase of the year between February and April, when they reduce their consumption and enter brief periods of torpor. Males begin hibernating first, while females that have reproduced start later. During the period of hibernation, the animals average 13 separate bouts of torpor, which are broken up by periods of arousal lasting 1.2 days on average. These interruptions tend to coincide with warmer periods. Males end their hibernation period in mid-June, while reproductive females return to full activity in July and August; nonreproductive females and immature echidnas may not end hibernation until two months later. During euthermia, the body temperature can vary by 4°C per day. The metabolic rate is around 30% of that of placental mammals, making it the lowest energy-consuming mammal. This figure is similar to that of other animals that eat ants and termites; burrowing animals also tend to have low metabolism generally.

Questions have arisen as to why echidnas hibernate, as it is seemingly unnecessary for survival; they begin their hibernation period while the weather is still warm, and food is generally always plentiful. One explanation of this phenomenon is echidnas want to be cautious with their energy reserves to maximize their foraging productivity. Another hypothesis is they are descended from ectothermic ancestors, but have taken to periodic endothermy for reproductive reasons, so the young can develop more quickly. Supporters of this theory argue males hibernate earlier than females because they finish their contribution to reproduction first, and they awake earlier to undergo spermatogenosis in preparation for mating, while females and young lag in their annual cycle. During the hibernation period, the animals stay in entirely covered shelter.

Short-beaked echidnas can live anywhere with a good supply of food. They locate food by smell, using sensors in the tips of their snouts, and regularly feast on ants and termites. This view is based on the echidna's method of shuffling around seemingly arbitrarily, and using its snout in a probing manner. A study of echidnas in New England has shown they tend to dig up scarab beetle larvae in spring when the prey are active, but eschew this prey when it is inactive; this has been used to support the conjecture that echidnas detect their prey using hearing. Vision is not believed to be significant in hunting, as blind animals have been observed to survive in the wild.

Echidnas use their strong claws to pull apart nests and rotting logs to gain access to their prey. They are selective of what types of ants and termites they target because some of their would-be prey secrete repulsive liquids. They also have a preference for the eggs, pupae and winged phases of the insects. Echidnas hunt most vigorously towards the end of winter and early in spring, when their fat reserves have been depleted after hibernation and/or nursing. At this time of the year, ants have high body fat, and the echidna targets their mounds. The animal also hunts beetles and earthworms, providing they are small enough to fit in a 5-mm gap. The proportion of ants and termites in their diets depends on the availability of prey, and termites make up a larger part in drier areas where they are more plentiful. However, termites are preferred, if available, as their bodies contain a smaller proportion of indigestible exoskeleton. Termites from the Rhinotermitidae family, however, are avoided due to their chemical defenses. Scarab beetle larvae are also a large part of the diet when and where available. In a study conducted in New England in New South Wales, 37% of the food intake consisted of beetle larvae, although the echidna had to squash the prey in its snout as it ingested it, due to size.

Echidnas are powerful diggers, using their clawed front paws to dig out prey and create burrows for shelter. They may rapidly dig themselves into the ground if they cannot find cover when in danger. They bend their belly together to shield the soft, unprotected part, and can also urinate, giving off a pungent liquid, in an attempt to deter attackers. Males also have single small spurs on each rear leg, believed to be a defensive weapon that has since been lost to the evolutionary process. Echidnas typically try to avoid confrontation with predators due to their lack of anatomical weaponry. Instead, they use the colour of their spines, which is similar to the vegetation of the dry Australian environment, to avoid detection. They have good hearing and tend to become stationary if sound is detected.

In Australia, they are most common in forested areas with abundant, termite-filled, fallen logs. In agricultural areas, they are most likely to be found in uncleared scrub; they may be found in grassland, arid areas, and in the outer suburbs of the capital cities. Little is known about their distribution in New Guinea. They have been found in southern New Guinea between Merauke in the west and the Kelp Welsh River, east of Port Moresby, in the east, where they may be found in open woodland.

Echidnas have the ability to swim, and have been seen cooling off near dams during high temperatures. They have also been seen crossing streams and swimming for brief periods in seas off Kangaroo Island. They swim with only the snout above water, using it as a snorkel.