Western spiny-tailed skink (Egernia stokesii badia)

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Western spiny-tailed skink
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Western spiny-tailed skink fact file

Western spiny-tailed skink description

KingdomAnimalia
PhylumChordata
ClassReptilia
OrderSquamata
FamilyScincidae
GenusEgernia (1)

The western spiny-tailed skink gains its Latin name from Admiral John Lort Stokes, an officer serving on the HMS Beagle during the time Charles Darwin made his famous voyage (2), A robust lizard with the cylindrical body and rather short limbs typical of a skink (3), it is olive- to reddish-brown in colour, with scattered paler brown and darker-edged scales which tend to form transverse bars. The belly is white, cream or yellow. The tail, which measures just a third of the snout-vent length, is strongly flattened and, as the common name suggests, heavily spined (4). In addition to the spiny tail, the scales of the body are also heavily keeled (4), helping to prevent predators from easily extracting the skink from crevices or hollows (5).

Also known as
Gidgee skink, gidgee spiny-tailed skink, Stoke’s egernia, Stoke’s skink.
Size
Snout-vent length: up to 19.4 cm (2)
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Western spiny-tailed skink biology

Like many skinks (3), the western spiny-tailed skink is most active during the day (5), basking and foraging within easy reach of its rocky shelters. The diet consists mainly of insects (4), although adults will also eat plant material, and the diet may change seasonally (8). Like many Egernia species, the western spiny-tailed skink has the habit of using specific defecating sites, resulting in small piles of faeces that may mark the group’s territory (4) (5) (7) (9).

The western spiny-tailed skink shows an unusual level of social complexity, living in stable, extended family groups of up to 17 individuals, consisting of breeding partners, offspring, and related adults (5) (9) (10). Group members appear to use chemical cues to recognise each other (5) (11) (12), and bask close together, as well as sharing shelters (9). Living in such a group may improve vigilance against predators, or allow offspring access to otherwise potentially limited food and refuges (5) (10) (13). Also unusually for a lizard, the western spiny-tailed skink is monogamous, with breeding pairs remaining together over many seasons (5) (14). The female gives birth to up to eight live young between February and March, after a gestation period estimated at three to four months (15). The newborn skinks average a snout-vent length of 6.7 centimetres (15), and take over five years to reach maturity, after which they may disperse to nearby groups (5) (9) (10). The lifespan of this species may be up to 25 years (5) (15).

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Western spiny-tailed skink range

While the species as a whole is found across Australia, in New South Wales, the Northern Territory, Queensland, South Australia and Western Australia (2) (4), the subspecies Egernia stokesii badia (western spiny-tailed skink) is found only in parts of Western Australia, where its range has been severely reduced (2) (5) (6).

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Western spiny-tailed skink habitat

The western spiny-tailed skink inhabits tall shrubland, open heath, woodland, and areas with limestone slabs, and requires hollow logs or rock crevices for shelter (4) (5) (6) (7).

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Western spiny-tailed skink status

Classified as Endangered (EN) on the IUCN Red List (1).

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Western spiny-tailed skink threats

The western spiny-tailed skink has declined in numbers and range as a result of overgrazing, habitat clearance and crop production (7) (6) (16). The region occupied by this subspecies has proved suitable for wheat cultivation, and most has been extensively cleared of standing and fallen timber, and now forms the north-eastern wheatbelt of Western Australia. In this area, very little suitable habitat now remains for the western spiny-tailed skink (7) (6), and introduced predators such as cats and foxes may also be a potential threat (17).

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Western spiny-tailed skink conservation

A number of conservation efforts are underway for the western spiny-tailed skink. A partnership between WWF-Australia, government and local communities has led to two projects, ‘Back from the Edge’ and ‘Back from the Brink’, which aim to raise awareness of threatened species in the Avon River Basin region of Western Australia, and which have already discovered two new populations of western spiny-tailed skink. WWF and the local government are also supporting communities and individuals in participating in conservation action in the region, and in managing the skink’s populations and habitat (17) (18). It will also be important to provide guidelines and incentives for landowners to reduce the impact of current land use practices (6). Further conservation measures recommended for this unusual lizard include translocations to suitable sites (16), as well as population surveys, research into its biology and ecology, genetic studies, and ensuring that secure, viable populations are maintained within reserves (6).

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Find out more

To find out more about the conservation of the western spiny-tailed skink see:

For more information on conservation in Australia see:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk
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Glossary

Gestation
The state of being pregnant; the period from conception to birth.
Keel
A projecting ridge along a flat or curved surface, particularly down the middle.
Monogamous
Having only one mate during a breeding season, or throughout the breeding life of a pair.
Snout-vent length
A standard measurement of body length of reptiles. The measurement is from the tip of the nose (snout) to the anus (vent), and excludes the tail.
Subspecies
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
Territory
An area occupied and defended by an animal, a pair of animals or a colony.
Translocation
When individual living organisms from one area are transferred and released or planted in another area.
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References

  1. IUCN Red List (October, 2009)
    http://www.iucnredlist.org/
  2. J. Craig Venter Institute: Reptiles Database (October, 2009)
    http://www.jcvi.org/reptiles/search.php
  3. Halliday, T. and Adler, K. (2002) The New Encyclopedia of Reptiles and Amphibians. Oxford University Press, Oxford.
  4. Cogger, H.G. (1996) Reptiles and Amphibians of Australia. Fifth Edition. Reed International, Chatswood, New South Wales.
  5. Chapple, D.G. (2003) Ecology, life-history, and behavior in the Australian scincid genus Egernia, with comments on the evolution of complex sociality in lizards. Herpetological Monographs, 17: 145 - 180.
  6. Cogger, H.G., Cameron, E.E., Sadlier, R.A. and Eggler, P. (1993) The Action Plan for Australian Reptiles. Australian Nature Conservation Agency, Canberra. Available at:
    http://www.environment.gov.au/biodiversity/threatened/publications/action/reptiles/index.html
  7. Department of the Environment, Water, Heritage and the Arts. (2009) Egernia stokesii badia - Western Spiny-tailed Skink. In: Species Profile and Threats Database. Department of the Environment, Heritage and the Arts, Canberra. Available at:
    http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=64483
  8. Duffield, G.A. and Bull, C.M. (1998) Seasonal and ontogenetic changes in the diet of the Australian skink Egernia stokesii. Herpetologica, 54(3): 414 - 419.
  9. Duffield, G.A. and Bull, C.M. (2002) Stable social aggregations in an Australian lizard, Egernia stokesii. Naturwissenschaften, 89: 424 - 427.
  10. Gardner, M.G., Bull, C.M., Cooper, S.J.B. and Duffield, G.A. (2001) Genetic evidence for a family structure in stable social aggregations of the Australian lizard Egernia stokesii. Molecular Ecology, 10: 175 - 183.
  11. Main, A.R. and Bull, C.M. (1996) Mother-offspring recognition in two Australian lizards, Tiliqua rugosa and Egernia stokesii. Animal Behaviour, 52: 193 - 200.
  12. Bull, C.M., Griffin, C.L., Lanham, E.J. and Johnston, G.R. (2000) Recognition of pheromones from group members in a gregarious lizard, Egernia stokesii. Journal of Herpetology, 34: 92 - 99.
  13. Lanham, E.J. and Bull, C.M. (2004) Enhanced vigilance in groups in Egernia stokesii, a lizard with stable social aggregations. Journal of Zoology, 263: 95 - 99.
  14. Gardner, M.G., Bull, C.M. and Cooper, S.J.B. (2002) High levels of genetic monogamy in the group-living Australian lizard Egernia stokesii. Molecular Ecology, 11: 1787 - 1794.
  15. Duffield, G.A. and Bull, C.M. (1996) Characteristics of the litter of the gidgee skink, Egernia stokesii. Wildlife Research, 23: 337 - 342.
  16. How, R.A., Dell, J. and Robinson, D.J. (2003) The western spiny-tailed skink, Egernia stokesii badia: declining distribution in a habitat specialist. Western Australian Naturalist, 24(2): 138 - 146.
  17. WWF-Australia: Rural communities help preserve rare western spiny-tailed skink (October, 2009)
    http://www.wwf.org.au/news/rural-communities-help-preserve-rare-western-spiny-tailed-skink/
  18. WWF: Biodiversity conservation in the Avon River Basin, Western Australia (October, 2009)
    http://www.panda.org/who_we_are/wwf_offices/australia/projects/index.cfm?uProjectID=AU0087
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Image credit

Western spiny-tailed skink  
Western spiny-tailed skink

© Rune Midtgaard

Rune Midtgaard
runemidtgaard@gmail.com
http://www.natureswindow.dk

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