Echidnas (Tachyglossidae)

views updated

Echidnas

(Tachyglossidae)

Class Mammalia

Order Monotremata

Family Tachyglossidae


Thumbnail description
Small to medium, terrestrial, invertebrate-feeding, egg-laying mammal, characterized by a head with large brain and narrow beak-like snout covered with leathery skin, minute mouth opening under the tip of the beak, no teeth, worm-like tongue, small external eyes, large ear slits, stocky, rounded body covered with spines and fur, powerful front digging limbs, and backwards rotated hind limbs

Size
16–40 in (40–100 cm); 5.5–35.2 lb (2.5–16 kg)

Number of genera, species
2 genera; 4 species

Habitat
Forests, grasslands, heath, shrublands, and woodlands

Conservation status
Endangered: 3 species; Lower Risk/Near Threatened: 1 species

Distribution
Australia and New Guinea

Evolution and systematics

Fossil records for echidnas are scarce. The first tachyglosssid fossil, a long-beaked echidna (Zaglossus robusta = Megalibgwilia), found in a gold mine at Gulgong, New South Wales in 1895 was about 15 million years old. Tachyglossus remains have been found in Pleistocene sediment (about 100,000 years old) at Mammoth Cave, Western Australia and in the Naracoorte Caves of South Australia. Fossil records show that long-beaked echidnas became extinct on mainland Australia in the late Pleistocene.

The divergence of present day echidnas and their relationship to other fossil monotremes from the Cretaceous (120 million years ago), are unknown.

The family Tachyglossidae is divided into two genera. Tachyglossus, the short-beaked echidna, consists of one species, T. aculeatus, and five subspecies. Zaglossus, the long-beaked echidna, has three species, with four subspecies of Z. bartoni. Zaglossus taxonomy is based on world museum collections.

Physical characteristics

Together with the platypus, echidnas are the world's only monotremes, or egg-laying mammals. They are sometimes referred to as "spiny anteaters" because they look like the hedgehog and the porcupine in that they are covered by sharp spines.

Echidnas have a domed shaped back with short stubby tail, no obvious neck, and a flat belly. Back and sides are covered with spines (modified hairs) of varying sizes and lengths. Fine to course hair covers the legs and belly and surrounds the spines. The panniculus carnosus, a muscle located under the skin and around the body allows echidnas to assume contortionist shapes from very round to nearly flat. This muscle also permits movement of individual spines and helps form the pouch in reproductively active females.

Short and long-beaked echidnas are easily distinguished by differences in size, body mass, and length of the beak. Appearance of ears and eyes are also different. Adult Zaglossus range 24–40 in (60–100 cm) in length, weigh

13.2–35.2 lb (6–16 kg), and have a 4.2 in (10.5 cm) beak, often displaying a downward curve. Adult Tachyglossus are 12–20 in (30–50 cm) long, weigh 5.5–15.4 lb (2.5–7 kg), and have a 2.1 in (5.5 cm) straight beak. Whereas Zaglossus often have small distinct pinna, Tachyglossus generally have no external ear. Eyes of Tachyglossus are nearly obscured by hairs, but surrounded by bare wrinkled skin in Zaglossus. Contrary to lore, echidnas see well and can learn using visual cues.

The thick, woolly hair and short spines of Zaglossus are most like the Tasmanian subspecies of Tachyglossus, T. a. setosus. Pelage density, color, and spine length differ between subspecies. The arid dwelling T. a. acanthion tend to have longer, thinner spines and less hair than the other mainland subspecies T. a. aculeatus. Pelage of Kangaroo Island, T. a. multiaculeatus, and Tasmania, T. a. setosus, subspecies varies from light straw-colored to very dark whereas mainland subspecies are uniformly dark. Albinism has been reported in most subspecies.

Front and back limbs have five toes, with one to three grooming claws on each hind foot. Articulation of the rotated hind limbs in the pelvic girdle gives echidnas extreme dexterity to scratch between spines on any part of the body. Arrangement of the muscles in relation to the short, stout limbs gives echidnas enormous strength for digging and climbing. The limbs of Zaglossus are twice as long as those of Tachyglossus.

Echidna body temperature is low compared to other mammals, 87.8–91.4°F (31–33°C) and individuals use torpor (lowering of body temperature and metabolic rate) at any time of the year. There is only one opening, the cloaca, for excretion of urinary, fecal, and reproductive products out of the body. It is not possible to tell the gender of an echidna by external features. All genitalia are located internally. Both males and females may retain a spur on the inside of the hind foot and both can contract abdominal muscles to form a pseudo-pouch. Echidnas can live in excess of 50 years.

Distribution

Short-beaked echidnas are found throughout Australia and in some parts of New Guinea. Long-beaked echidnas occur only in New Guinea and Salawati. They once inhabited parts of Australia, but died out about 20,000 years ago.

Habitat

Short-beaked echidnas are found in all types of native and exotic Australian habitats from sea level to alpine and from arid through tropical. Little is known about the distribution of T. a. lawesi in New Guinea; most records are from the south and southwest of the country. Long-beaked echidnas have been found from sea level to 12,500 ft (4,150 m), primarily in areas of higher rainfall.

Behavior

Echidnas are solitary living, extremely mobile and have home ranges up to 494 acres (200 ha). Home ranges of several animals overlap and are not defended as territories. Individuals do not interact, forage communally, or use the same shelter sites. Short-beaked echidnas are active both day and night, depending on time of year and locality. They avoid the heat of the day because they do not sweat or pant. Long-beaked echidnas are thought to be totally nocturnal, but little is known about their natural history.

Echidnas rarely vocalize. Apart from audible snuffing sounds, there are a few reports of soft "cooing" or "purring."

Feeding ecology and diet

Whereas short-beaked echidnas feed on all types of invertebrate species found in the soil or rotting wood; long-beaked echidnas feed primarily on earthworms. The tongue of the long-beaked echidna is grooved and has three rows of backward directed keratinous spines at the tip, that help extract worms from the ground. The tongue of the short-beaked echidna is lubricated with a sticky secretion, extends up to 7 in (18 cm) beyond the tip of the beak, and has an agile tip for drawing insects into the mouth. Echidnas have no teeth, but grind their food between a set of tiny keratinized spines located on the base of the tongue and the roof of the mouth. Echidnas find their prey using acute senses of smell and hearing. They also sense vibrations with their beak.

Reproductive biology

Short-beaked echidnas are sexually mature at five to seven years of age. Courtship and breeding occur during the Australian winter through spring, June to September. At the beginning of the courtship period, male echidnas abandon their solitary life style in search of a female. A group of males following a single female is called an echidna train. Courtship lasts between one and four weeks, with up to 10 males accompanying, prodding, and following a female until she is receptive. Males then compete, by shoving each other head on head, to dig a trench beside the female. When only one male remains, he completes the mating trench that prevents him from rolling over as he lifts the female and places his tail under hers, cloaca on cloaca. Copulation, which lasts between 30 and 120 minutes, is the only time that the penis is outside the body. A female mates only once during the reproductive season. After mating, males and females return to a solitary life style.

During the 22-day gestation the mammary glands of the female begin to swell and form a longitudinal pouch on the belly. In a sitting position, the female extends her cloaca and lays a single egg directly into the pouch. The 0.6 in (15 mm)

egg, about the diameter of 10-cent coin, has a soft, leathery shell. After 10.5 days of incubation, the young echidna, called a "puggle" hatches. Weighing only 0.0105 oz (300 mg), it takes 10 puggles to weigh as much as a 10-cent coin. There are no teats or nipples for the puggle to attach to. It clings to the hairs on the mother's belly with minuscule but well developed front limbs. Milk is suckled from the milk patches, areolae with specialized hairs, located anteriorly and on either side of the pouch. The puggle remains in the pouch for about 50 days and increases its body mass 85,000%. When too large to carry, the female leaves the young in a secure nursery burrow and returns for two hours every five days to suckle it. At weaning, seven months of age, the young weigh 1.7–3.3 lb (800–1,500g), depending on the size of the mother. There is no mother/offspring relationship after weaning. Young leave the natal area at about one year of age and travel up to 25 mi (40 km) to establish a home range. Most sexually mature females produce only one young every three to five years.

There have been no observations on the reproductive ecology of long-beaked echidnas. Their urogenital systems are identical to Tachyglossus and their reproductive biology is believed to be similar. No one has ever seen a pouch or burrow young Zaglossus in the wild and there are no specimens of young in world museum collections.

Conservation status

Although T. aculeatus have a wide distribution, populations are not large. Throughout Australia numbers have declined due to loss of habitat, predation by feral foxes, cats, dogs, and pigs, as well as roads, electric fences, and herbicide/pesticide use. IUCN lists this species as Lower Risk/Near Threatened. Zaglossus spp. are listed as Endangered throughout their range. Populations have disappeared primarily due to hunting which increased with human densities and a breakdown in traditional taboos.

Significance to humans

Some aboriginal groups hunted and ate short-beaked echidnas while other groups revered them as a totem. Early Europeans used echidna fat as a harness dressing or lubricant. Today short-beaked echidnas are an Australian icon used by many grass roots organizations to represent their down-to-earth, geton-with-it work ethics. In 2000 the echidna was an Olympic mascot. Long-beaked echidnas are hunted for food in some areas of New Guinea. As a member of the oldest surviving group of mammals echidnas are symbolic of species sustainability.

Common name/Scientific name/Other common namesPhysical characteristicsHabitat and behaviorDistributionFoodConservation status
Short-beaked echidna
Tachyglossus aculeatus
Stocky, rounded body covered with spines and fur. 12–20 in (30–50 cm) long; weight 5.5–15.4 lb (2.5–7 kg); has a 2.1 in (5.5 cm) straight beak. Generally have no external ear and eyes are nearly obscured by hairs.Found in all types of Australian habitats—sea level to alpine, and arid to tropical. Solitary; active both day and night.Throughout Australia and in some parts of New Guinea.All types of invertebrate species found in soil or rotting wood.Lower Risk/Near Threatened
Long-beaked echidna
Zaglossus spp.
Stocky, rounded body covered with spines and fur. 24–40 in (60–100 cm) long; weight 13.2–35.2 lb (6–16 kg); has a 4.2 in (10.5 cm) beak, often displaying a downward curve. Often have small distinct external ears, and eyes surrounded by bare wrinkled skin.Found from sea level to 12,500 ft (4,150 m), primarily in areas of higher rainfall. Solitary; thought to be totally nocturnal.New Guinea and Salawati.Primarily earthworms.Endangered

Resources

Books

Augee, M. L., ed. Monotreme Biology. Mosman: Royal Zoological Society of New South Wales, 1978.

Augee, M. L., ed. Platypus and echidnas. Mosman: Royal Zoological Society of New South Wales, 1992.

Augee, M. L., and B. Gooden. Echidnas of Australia and New Guinea. Kensington: New South Wales University Press, 1993.

Baille, J., and B. Groombridge, eds. IUCN Red List of Threatened Animals. Gland, Switzerland: International Union of Conservation for Nature, 1996.

Flannery, T. F. Mammals of New Guinea. Sydney: Reed Books, 1995.

Griffiths, M. Echidnas. Oxford and New York: Pergamon Press, 1968.

Griffiths, M. The Biology of the Monotremes. New York: Academic Press, 1978.

Nicol, S. C., and N. A. Andersen. "Patterns of hibernation of echidnas in Tasnamia." In Life in the Cold: Tenth International Hibernation Symposium, edited by G. Heldmaier and M. Klingenspor. Berlin: Springer, 2000.

Rismiller, P. D. The Echidna, Australia's Enigma. Southport, Connecticut: Hugh Lauter Levin Associates, 1999.

Rismiller, P. D., and M. W. McKelvey. "Sex, torpor and activity in temperate climate echidnas." In Adaptations to the Cold, edited by F. Geiser, A. J. Hulbert, and S. C. Nicol. Armidale: University of New England Press, 1996.

Wells R. T. and Pledge, N. S. "Vertebrate Fossils." In Natural History of the South East, edited by M. J. Tyler, C. R. Twidale, J. K. Ling and J. W. Holmes. Adelaide: Royal Society of South Australia, 1983.

Periodicals

Abensperg-Traun, M. "A study of home range, movements and shelter use in adult and juvenile echidnas Tachyglossus aculeatus (Monotremata: Tachyglossidae) in Western Australian wheatbelt reserves." Australian Mammalogy 14 (1991): 13–21.

Dulhunty, J. A. "Potassium-Argon basalt dates and their significance in the Ilford-Mudgee-Gulgong region." Proceedings of the Royal Society of New South Wales 104 (1971): 9–44.

Flannery, T. F., and C. P. Groves. "A revision of the genus Zaglossus (Monotremata, Tachyglossidae) with description of new species and subspecies." Mammalia 62, no. 3 (1998): 367–396.

Gates, G. A. "Vision in the monotreme anteater (Tachyglossus aculeatus)." Australian Zoologist 20 (1978): 147–169.

Grigg, G. C., L. A. Beard, and M. L. Augee. "Hibernation in a monotreme, the echidna Tachyglossus aculeatus." Comparative Biochemistry and Physiology A 92 (1989): 609–612.

Murray, P. F. "Late Cenozoic monotreme anteaters." Australian Zoologist 20 (1978): 29–55.

Pledge, N. S. "Giant echidnas in South Australia." South Australian Naturalist 2 (1980): 27–30.

Rismiller, P. D., and M. W. McKelvey. "Frequency of breeding and recruitment in the short-beaked echidna, Tachyglossus aculeatus." Journal of Mammalogy 81, no. 1 (2000): 1–17.

Other

Echidna the Survivor. Documentary videotape. Australian Broadcasting Corporation, 1995.

Peggy Rismiller, PhD

About this article

Echidnas (Tachyglossidae)

Updated About encyclopedia.com content Print Article