Short-beaked echidna

Appearance

Short-beaked echidnas are typically 30 to 45 cm in length, with 75 mm of snout, and weigh between 2 and 5 kg. However, the Tasmanian subspecies, "T. a. setosus", is smaller than its Australian mainland counterparts. Because the neck is not externally visible, the head and body appear to merge.

The earholes are on either side of the head, with no external pinnae. The eyes are small, about 9 mm in diameter and at the base of the wedge-shaped snout.

The nostrils and the mouth are at the distal end of the snout; the mouth cannot open wider than 5 mm. The body of the short-beaked echidna is, with the exception of the underside, face and legs, covered with cream-coloured spines. The spines, which may be up to 50 mm long, are modified hairs, mostly made of keratin.

Insulation is provided by fur between the spines, which ranges in colour from honey to a dark reddish-brown and even black; the underside and short tail are also covered in fur. Colouration of the fur and spines varies with geographic location. The echidna's fur may be infested with what is said to be the world's largest flea, "Bradiopsylla echidnae", which is about 4 mm long.

The limbs of the short-beaked echidna are adapted for rapid digging; they are short and have strong claws. Their strong and stout limbs allow it to tear apart large logs and move paving stones, and one has been recorded moving a 13.5-kg stone; a scientist also reported a captive echidna moved a refrigerator around the room in his home. The power of the limbs are based on strong musculature, particularly around the shoulder and torso areas. The mechanical advantage of its arm is greater than that of humans, as its biceps connects the shoulder to forearm at a point further down than for humans, and the chunky humerus allows more muscle to form.

The claws on the hind feet are elongated and curved backward to enable cleaning and grooming between the spines. Like the platypus, the echidna has a low body temperature—between 30 and 32°C —but, unlike the platypus, which shows no evidence of torpor or hibernation, the body temperature of the echidna may fall as low as 5°C.

The Echidna does not pant or sweat and normally seeks shelter in hot conditions. Despite the inability to sweat, echidnas still lose water as they exhale. The snout is believed to be crucial in restricting this loss to sustainable levels, through a bony labyrinth that has a refrigerator effect and helps to condense water vapour in the breath. The echidna does not have highly concentrated urine, and around half of the estimated daily water loss of 120 g occurs in this manner, while most of the rest is through the skin and respiratory system. Most of this is replenished by its substantial eating of termites—one laboratory study reported it would ingest around 147 g a day, most of which was water. This can be supplemented by drinking water if available, or licking morning dew from flora.

Like all monotremes, it has one orifice, the cloaca, for the passage of faeces, urine and reproductive products. The male has internal testes, no external scrotum and a highly unusual penis with four knobs on the tip, which is nearly a quarter of his body length when erect. The gestating female develops a pouch on her underside, where she raises her young.

Naming

The short-beaked echidna was first described by George Shaw in 1792. He named the species "Myrmecophaga aculeata", thinking it might be related to the giant anteater. Since Shaw first described the species, its name has undergone four revisions: from "M. aculeata" to "Ornithorhynchus hystrix", "Echidna hystrix", "Echidna aculeata" and finally, "Tachyglossus aculeatus". The name "Tachyglossus" means "quick tongue", in reference to the speed with which the echidna uses its tongue to catch ants and termites, and "aculeatus" means "spiny" or "equipped with spines".

The short-beaked echidna is the only member of its genus, sharing the family Tachyglossidae with the extant species of the genus "Zaglossus" that occur in New Guinea. "Zaglossus" species, which include the western long-beaked, Sir David's long-beaked and eastern long-beaked echidnas, are all significantly larger than "T. aculeatus", and their diets consist mostly of worms and grubs rather than ants and termites. Species of the Tachyglossidae are egg-laying mammals; together with the related family Ornithorhynchidae, they are the only extant monotremes in the world.

The five subspecies of the short-beaked echidna are each found in different geographical locations. The subspecies also differ from one another in their hairiness, spine length and width, and the size of the grooming claws on their hind feet.

⤷  "T. a. acanthion" is found in Northern Territory and Western Australia.
⤷  "T. a. aculeatus" is found in Queensland, New South Wales, South Australia and Victoria.
⤷  "T. a. lawesii" is found in coastal regions and the highlands of New Guinea, and possibly in the rainforests of Northeast Queensland.
⤷  "T. a. multiaculeatus" is found on Kangaroo Island.
⤷  "T. a. setosus" is found on Tasmania and some islands in Bass Strait.

The earliest fossils of the short-beaked echidna date back around 15 million years ago to the Pleistocene era, and the oldest specimens were found in caves in South Australia, often with fossils of the long-beaked echidna from the same period. The ancient short-beaked echidnas are considered to be identical to their contemporary descendants except the ancestors are around 10% smaller. This "post-Pleistocene dwarfing" affects many Australian mammals. Part of the last radiation of monotreme mammals, echidnas are believed to have evolutionally diverged from the platypus around 65 million years ago, between the Cretacious and Tertiary periods. However, the echidna's pre-Pleistocene heritage has not been traced yet, and the lack of teeth on the fossils found thus far have made it impossible to use dental evidence.

The short-beaked echidna was commonly called the spiny anteater in older books, though this term has fallen out of fashion since the echidna bears no relation to the true anteaters. It has a variety of names in the indigenous languages of the regions where it is found. The Noongar people from southwestern Western Australia call it the "nyingarn". In Central Australia southwest of Alice Springs, the Pitjantjatjara term is "tjilkamata" or "tjirili", from the word "tjiri" for spike of porcupine grass ". The word can also mean slowpoke. In central Cape York Peninsula, it is called " kekoywa" in Pakanh, where "minha" is a qualifier meaning 'meat' or 'animal', "ekorak" in Uw Oykangand and "egorag" in Uw Olkola, where "inh-" is a qualifier meaning 'meat' or 'animal'.
In the highland regions of southwestern New Guinea, it is known as the "mungwe" in the Daribi and Chimbu languages.

Status

The short-beaked echidna is common throughout most of temperate Australia and lowland New Guinea, and is not listed as endangered. In Australia, it remains widespread across a wide range of conditions, including urban outskirts, coastal forests and dry inland areas, and is especially widespread in Tasmania and on Kangaroo Island.

Behavior

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 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, 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. 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.

Reproduction

The solitary short-beaked echidna looks for a mate between May and September; the precise timing of the mating season varies with geographic location. In the months before the mating season, the size of the male's testes increases by a factor of three or more before spermatogenesis occurs. Both males and females give off a strong, musky odour during the mating season, by turning their cloacas inside out and wiping them on the ground, secreting a glossly liquid believed to be an aphrodisiac. During courtship—observed for the first time in 1989—males locate and pursue females. Trains of up to 10 males, often with the youngest and smallest male at the end of the queue, may follow a single female in a courtship ritual that may last for up to four weeks; the duration of the courtship period varies with location. During this time, they forage for food together, and the train often changes composition, as some males leave and other join the pursuit. In cooler parts of their range, such as Tasmania, females may mate within a few hours of arousal from hibernation.

Before mating, the male smells the female, paying particular attention to the cloaca. This process can take a few hours, and the female can reject the suitor by rolling herself into a ball. After prodding and sniffing her back, the male is often observed to roll the female onto her side and then assume a similar position himself so the two animals are abdomen to abdomen, having dug a small crater in which to lie. They can lie with heads facing one another, or head to rear. If more than one male is in the vicinity, fighting over the female may occur. Each side of the bilaterally symmetrical, rosette-like, four-headed penis [similar to that of reptiles and 7 centimetres in length] is used alternately, with the other half being shut down between ejaculations. Sperm bundles of around 100 each appear to confer increased sperm motility, which may provide the potential for sperm competition between males. This process takes between a half and three hours. Each mating results in the production of a single egg, and females are known to mate only once during the breeding season; each mating is successful.

Fertilisation occurs in the oviduct. Gestation takes between 21 and 28 days after copulation, during which time the female constructs a nursery burrow. Following the gestation period, a single, rubbery-skinned egg between 13 and 17 mm in diameter and 1.5 and 2.0 g in weight is laid from her cloaca directly into a small, backward-facing pouch that has developed on her abdomen. The egg is ovoid, leathery, soft, and cream-coloured. Between laying and hatching, some females continue to forage for food, while others dig burrows and rest there until hatching. Ten days after it is laid, the egg hatches within the pouch. The embryo develops an "egg tooth" during incubation, which it uses to tear open the egg; the tooth disappears soon after hatching.

Hatchlings are about 1.5 centimetres long and weigh between 0.3 and 0.4 grams. After hatching, young echidnas are known as "puggles". Although newborns are still semitranslucent and still surrounded by the remains of the egg yolk, and the eyes are still barely developed, they already have well-defined front limbs and digits that allow them to climb on their mothers' bodies. Hatchlings attach themselves to their mothers' milk areolae, specialised patches on the skin that secrete milk—monotremes lack nipples—through about 100–150 pores. The puggles were thought to have imbibed the milk by licking the mother's skin, but they are now thought to feed by sucking the areolae.

They have been observed ingesting large amounts during each feeding period, and mothers may leave them unattended in the burrow for between five and 10 days to find food. Studies of captives have shown they can ingest milk once every two or three days and then increase their mass by 20% in one milk-drinking session lasting between one and two hours. Around 40% of the milk weight is converted into body mass, and as such, a high proportion of milk is converted into growth; a correlation with the growth of the puggle and its mother's size has been observed. By the time the puggle is around 200 g, it is left in the burrow while the mother forages for food, and it reaches around 400 g after around two months. Juveniles are eventually ejected from the pouch at around two to three months of age, because of the continuing growth in the length of their spines. During this period, the young are left in covered burrows while the mothers forage, and the young are often preyed upon. Suckling gradually decreases until juveniles are weaned at about six months of age. The duration of lactation is about 200 days, and the young leave the burrow after 180 to 205 days, usually in January or February, at which time they weigh around 800 and 1,300 g. There is no contact between the mother and young after this point.

The composition of the milk secreted by the mother changes over time. At the moment of birth, the solution is dilute and contains 1.25% fat, 7.85% protein, and 2.85% carbohydrates and minerals. Mature milk has much more concentrated nutrients, with 31.0, 12.4 and 2.8% of the aforementioned nutrients, respectively. Near weaning, the protein level continues to increase; this may be due to the need for keratin synthesis for hair and spines, to provide defences against the cold weather and predators.

The principal carbohydrate components of the milk are fucosyllactose and saialyllactose; it has a high iron content, which gives it a pink colour. The high iron content and low levels of free lactose contrasts with other eutherian mammals. Lactose production is believed to proceed along the same lines as in the platypus.

The age of sexual maturity is uncertain, but may be four to five years. A 12-year field study found the short-beaked echidna reaches sexual maturity between five and 12 years of age, and the frequency of reproduction varies from once every two years to once every six years. The short-beaked echidna can live as long as 45 years in the wild, and the longest-lived echidna in captivity reached 49 years of age in a zoo in Philadelphia in the US. Echidnas contrast to other mammals in that their rates of reproduction and metabolism are lower, and they live longer, as though in slow motion, something caused, at least in part, by their low body temperature, which rarely exceeds 33°C, even when they are not hibernating.

Like its fellow monotreme the platypus, the short-beaked echidna has a system of multiple sex chromosomes, in which males have four Y chromosomes and five X chromosomes. Male individuals appear to be X1Y1X2Y2X3Y3X4Y4X5, while females are X1X1X2X2X3X3X4X4X5X5. Weak identity between chromosomes results in meiotic pairing that yields only two possible genotypes of sperm, X1X2X3X4X5 or Y1Y2Y3Y4, thus preserving this complex system.

Cultural

Short-beaked echidnas feature in the animistic culture of indigenous Australians, including their visual arts and stories. The species was a totem for some groups, including the Noongar people from Western Australia. Many groups have myths about the animal; one myth explains it was created when a group of hungry young men went hunting at night and stumbled across a wombat. They threw spears at the wombat, but lost sight of it in the darkness. The wombat adapted the spears for its own defence and turned into an echidna. Another story tells of a greedy man who kept food from his tribe; warriors speared him and he crawled away into the bushes, where he turned into an echidna, the spears becoming his spines.

The short-beaked echidna is an iconic animal in contemporary Australia, notably appearing on the Australian five-cent coin, and on a A$200 commemorative coin released in 1992. The short-beaked echidna has been included in several postal issues; it was one of four native species to appear on Australian postage stamps in 1974, when it was on the 25-cent stamp; it appeared on a 37-cent stamp in 1987, and in 1992 it was on the 35-cent stamp. The anthropomorphic echidna "Millie" was a mascot for the 2000 Summer Olympics. Knuckles the Echidna, from the Sonic the Hedgehog series is also based on the short-beaked echidna.