|TheShort-beaked Echidna (Tachyglossus aculeatus), also known as the Spiny Anteater because of its diet of ants and termites, is one of four living species of echidna and the only member of the genus Tachyglossus. The Short-beaked Echidna is covered in fur and spines and has a distinctive snout and a specialized tongue, which it uses to catch its prey at a great speed. Like the other extant monotremes, the Short-beaked Echidna lays eggs; the monotremes are the only group of mammals to do so.
The species is found throughout Australia, where it is the most widespread native mammal, and in coastal and highland regions of southwestern New Guinea, where it is known as the Mungwe in the Daribi and Chimbu languages. It is not threatened with extinction, but human activities, such as hunting, habitat destruction, and the introduction of foreign predatory species and parasites, have reduced the distribution of the Short-beaked Echidna in Australia.
Short-beaked Echidnas are typically 30 to 45 centimetres (12-18 in) in length, have a 75-millimetre (3 in) snout, and weigh between two and five kilograms (4.5-11 lb). However, the Tasmanian subspecies, T. a. setosus, is larger than its Australian mainland counterparts. Because the neck is not externally visible, the head and body appear to merge together. The earholes are on either side of the head, with no external pinnae. The eyes are small and at the base of the wedge-shaped snout. The nostrils and the mouth are at the distal end of the snout; the mouth of the Short-beaked Echidna 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 (2 in) 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, their limbs are short and have strong claws. The claws on the hind feet are elongated and curve backwards to enable cleaning and grooming between the spines. Like the Platypus it has a low body temperature Â— between 30 and 32 Â°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 Â°C. The Echidna does not pant or sweat and normally seeks shelter in hot conditions. In autumn and winter the Echidna shows periods of torpor or deep hibernation. Because of the low body temperature of the Short-beaked Echidna, it becomes sluggish in very hot and very cold weather. Like all monotremes, it has one orifice for the passage of faeces, urine and reproductive products, which is known as the cloaca. The male has internal testes, no external scrotum and a highly unusual penis with four knobs on the tip. The gestating female develops a pouch on its underside, where it raises its young.
A Short-beaked Echidna curled into a ball; the snout is visible on the right.
The musculature of the Short-beaked Echidna has a number of unusual aspects. The panniculus carnosus is an enormous muscle that is just beneath the skin and covers the entire body. By contraction of various parts of the panniculus carnosus, the Short-beaked Echidna can change shapeÂ—the most characteristic shape change is achieved by rolling itself into a ball when threatened, protecting its belly and presenting a defensive array of sharp spines. It has one of the shortest spinal cords of any mammal, extending only as far as the thorax.
The musculature of the face, jaw and tongue is specialised to allow the Echidna to feed. The tongue of the Short-beaked Echidna is the animal’s sole means of catching prey, and can protrude up to 180 mm (8 in) outside the snout. The tongue is sticky because of the presence of glycoprotein-rich mucous, which both lubricates movement in and out of the snout and helps to catch ants and termites, which adhere to it. Protrusion of the tongue is achieved by contracting the circular muscles that change the shape of the tongue and force it forward, and contraction of two genioglossal muscles attached to the caudal end of the tongue and to the mandible. The protruded tongue is stiffened by the rapid flow of blood, allowing it to penetrate wood and soil. Retraction requires the contraction of two internal longitudinal muscles, known as the sternoglossi. When the tongue is retracted, the prey is caught on backward-facing keratinous “teeth”, located along the roof of the buccal cavity, allowing the animal both to capture and grind food.The tongue moves with great speed, and has been measured to move in and out of the snout 100 times a minute.
Numerous physiological adaptations aid the lifestyle of the Short-beaked Echidna. Because the animal burrows, it can tolerate very high levels of carbon dioxide in inspired air, and will voluntarily remain in situations where carbon dioxide concentrations are high. Its ear is sensitive to low-frequency sound, which may be ideal for detecting sounds emitted by termites and ants underground. The leathery snout is covered in mechano- and thermoreceptors, which provide information about the surrounding environment. The Short-beaked Echidna has a well-developed olfactory system, which may be used to detect mates and prey. It has a highly sensitive optic nerve, and has been shown to have visual discrimination and spatial memory comparable to those of a rat. The brain and central nervous system of the Short-beaked Echidna have been extensively studied for evolutionary comparison with placental mammals. The Short-beaked Echidna has the largest prefrontal cortex with respect to body size of any mammal, it shows rapid eye movement during sleep, and its brain has been shown to contain a claustrum that is similar to placental mammals, linking this structure to their common ancestor.
Ecology and behaviour
No systematic study of the ecology of the Short-beaked Echidna has been published; however, there have been studies of several aspects of their ecological behaviour. Short-beaked Echidnas 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, but range over a wide area. Short-beaked Echidnas are typically active in the daytime; however, 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 pattern of activity, becoming crepuscular or nocturnal. They can tolerate cold temperatures, and hibernate during the winter in very cold regions.
Short-beaked Echidnas can live anywhere that has a good supply of food. Short-beaked Echidnas locate food by smell, using sensors in the tip of their snout, and regularly feast on ants and termites. They 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.
In Australia they are most common in forested areas where there are 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, to the Kelp Welsh River, east of Port Moresby in the east, where they may be found in open woodland.
The underside of a female Short-beaked Echidna; the pouch which carries eggs is towards the rear of the abdomen.
The solitary Short-beaked Echidna looks for a mate between May and September; the precise timing of the mating season varies with geographic location. Both males and females give off a strong odour during the mating season. During courtship Â— observed for the first time in 1989 Â— males locate and pursue females. Trains of up to ten males 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. 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. The male is often observed to roll the female onto her side and then assumes a similar position so that the two animals are abdomen to abdomen. Each side of the bilaterally symmetrical, rosettelike 4 headed penis [similar to reptiles] is used alternately, with the other half being shut down between ejaculations. Sperm bundles of ~100 each, appears to confer increased sperm motility, which may provide the potential for sperm competition between males. 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, during which time the female constructs a nursery burrow. Following the gestation period, a single rubbery-skinned egg between 13 and 17 millimetres in diameter is laid directly into a small, backward-facing pouch that has developed on her abdomen. 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 cm long and weigh between 0.3 and 0.4 grams.After hatching, young Echidnas are known as puggles. Hatchlings attach themselves to their mothers’ milk areolae, a specialised patch on the skin that secretes milk (monotremes lack nipples). The way in which puggles imbibe the milk is not yet known, but they have been observed ingesting large amounts during each feeding period, since mothers may leave them unattended in the burrow for between five and ten days. The principal components of the milk are fucosyllactose and saialyllactose; it is high in iron content, giving it a pink colour. 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. 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 between 180 and 240 days.
The age of sexual maturity is uncertain, but may be four to five years. A twelve-year field study, published in 2003, found that the Short-beaked Echidna reached sexual maturity between five and 12 years of age, and that 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.
The Short-beaked Echidna is common throughout most of temperate Australia and lowland New Guinea, and is not listed as endangered. In Australia, the number of Short-beaked Echidnas has been less affected by land clearing than have some other species, since Short-beaked Echidnas do not require a specialised habitat beyond a good supply of ants and termites. Despite their spines, they are preyed on by birds, the Tasmanian Devil, cats, foxes and dogs. They were eaten by indigenous Australians and the early European settlers of Australia. The most common threats to the animal in Australia are motorised vehicles and habitat destruction, which have led to localised extinction. Infection with the introduced parasite Spirometra erinaceieuropaei is fatal for the Echidna. The Wildlife Preservation Society of Queensland runs an Australia-wide survey called Echidna Watch to monitor the species in Australia.
Captive breeding is difficult, partly due to the relatively infrequent breeding cycle. Only five zoos have managed to breed a captive Short-beaked Echidna, but no captive-bred young have survived to maturity. This has conservation implications for the endangered species of echidna from the genus Zaglossus, and to a lesser extent for the Short-beaked Echidna.