''Cryptoblepharus egeriae'', also known commonly as the blue-tailed shinning-skink, the Christmas Island blue-tailed shinning-skink, and the Christmas Island blue-tailed skink, is a

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia al ...

in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Scincidae that was once endemic to

Christmas Island Christmas Island, officially the Territory of Christmas Island, is an Australian external territory comprising the island of the same name. It is located in the Indian Ocean, around south of Java and Sumatra and around north-west of the ...

. The Christmas Island blue-tailed skink was discovered in 1888. (''Ablepharus egeriae'', new species, pp. 535–536). It was formerly the most abundant reptile on the island, and occurred in high numbers particularly near the human settlement. However, the Christmas Island blue-tailed skink began to decline sharply outwardly from the human settlement by the early 1990s, which coincided with the introduction of a predatory snake and the introduction of the yellow crazy ant ('' Anoplolepis gracilipes'') in the mid-1980s. By 2006, the Christmas Island blue-tailed skink was on the endangered animals list, and by 2010 the Christmas Island blue-tailed skink was

extinct in the wild A species that is extinct in the wild (EW) is one that has been categorized by the International Union for Conservation of Nature as known only by living members kept in captivity or as a naturalized population outside its historic range due t ...

. From 2009-2010, parks Australia and

Taronga Zoo Taronga Zoo is a zoo located in Sydney, New South Wales, Australia, in the suburb of Mosman, on the shores of Sydney Harbour. The opening hours are between 9:30 a.m. to 5 p.m. Taronga is an Aboriginal word meaning 'beautiful water view'. ...

started a captive breeding program, which has prevented total extinction of the species.

Etymology

The specific name, ''egeriae'', is in honor of HMS ''Egeria''. Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). ''The Eponym Dictionary of Reptiles''. Baltimore: Johns Hopkins University Press. xiii + 296 pp. . (''Cryptoblepharus egeriae'', p. 81).

Description

The Christmas island blue-tailed skink typically grows to a snout-to-vent length (SVL) of . It can be identified by its small black body with two yellow stripes running down the skink's back and onto its vibrant blue tail. The skink can use its blue tail to draw a predator’s attention away from its body by separating its tail from its body. The bright color of the skink's tail means predators are much more likely to notice the tail than the skink's black body.

Diet

The Christmas Island blue-tailed skink is a forager known as an

insectivore A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores wer ...

. Its diet primarily consists of

crickets Crickets are orthopteran insects which are related to bush crickets, and, more distantly, to grasshoppers. In older literature, such as Imms,Imms AD, rev. Richards OW & Davies RG (1970) ''A General Textbook of Entomology'' 9th Ed. Methuen 88 ...

beetles Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, Elytron, elytra, distinguishing them from most other insects. The Coleoptera, wit ...

flies Flies are insects of the Order (biology), order Diptera, the name being derived from the Ancient Greek, Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwing ...

grasshoppers Grasshoppers are a group of insects belonging to the suborder Caelifera. They are among what is possibly the most ancient living group of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago. Grasshop ...

spiders Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species di ...

, and

earthworms An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. T ...

. It will occasionally eat some

vegetation Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic charact ...

, though insects remain its primary source of food. Because of its small size, the Christmas Island blue-tailed skink forages for its food on the ground, over exposed rocks and low-lying vegetation, and will generally only eat prey that are slower moving.

Reproduction

For the Christmas Island blue-tailed skink, the first

breeding season Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and ch ...

occurs when males and females are approximately one year old. The Christmas Island blue-tailed skink typically lives for seven years in the wild, six of which are active breeding years. The male Christmas Island blue-tailed skink will demonstrate

courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private ...

behaviour when trying to find a mate. The female Christmas Island blue-tailed skink will emit biochemicals for the males to smell, letting them know that the female is in her fertile stage of

reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – " offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual o ...

. Male Christmas Island blue-tailed skinks will often fight each other to win a female mate during breeding season. These skinks are

polygamous Crimes Polygamy (from Late Greek (') "state of marriage to many spouses") is the practice of marrying multiple spouses. When a man is married to more than one wife at the same time, sociologists call this polygyny. When a woman is married ...

which increases their chance of having offspring. Once the female Christmas Island blue-tailed skink has been fertilized, being

oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), a ...

, it will generally lay two eggs at a time, with a 75-day

incubation period Incubation period (also known as the latent period or latency period) is the time elapsed between exposure to a pathogenic organism, a chemical, or radiation, and when symptoms and signs are first apparent. In a typical infectious disease, the in ...

Distribution

The Christmas Island blue-tailed skink was

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

until the late 1990s when it could be found all over the island. It currently exists in captive populations on Christmas Island, at Taronga Zoo, and on a small island (Pulu Blan) in the

Cocos (Keeling) Islands ) , anthem = "'' Advance Australia Fair''" , song_type = , song = , image_map = Australia on the globe (Cocos (Keeling) Islands special) (Southeast Asia centered).svg , map_alt = Location of the Cocos (Keeling) Islands , map_caption = ...

where it has been released as part of an assisted colonization trial.

Conservation Efforts

The threat of extinction is largely attributed to introductions of invasive species, including a predatory wolf snake and the yellow crazy ant which were unintentionally brought to the island in the 1980s. The Christmas Island blue-tailed skink is now extinct in the wild. However,

currently has an active breeding program hosted by

Taronga Conservation Society The Taronga Conservation Society is a Government of New South Wales agency responsible for Taronga Zoo Sydney and the Taronga Western Plains Zoo in New South Wales, Australia Australia, officially the Commonwealth of Australia, is a Sove ...

, which originated from 66 skinks that were brought into captivity before their population was wiped out. The breeding program has been running for over a decade, with the goal of releasing some of the skinks back into their native habitat. Since the Taronga Conservation Society conservation efforts began, 300 skinks have been introduced to the

Cocos Islands ) , anthem = "''Advance Australia Fair''" , song_type = , song = , image_map = Australia on the globe (Cocos (Keeling) Islands special) (Southeast Asia centered).svg , map_alt = Location of the Cocos (Keeling) Islands , map_caption = ...

. The genome of the blue-tailed skink (along with the

Lister's gecko ''Lepidodactylus listeri'', also known commonly as Lister's gecko or the Christmas Island chained gecko, is a species of gecko, a lizard in the family Gekkonidae, endemic to Christmas Island in the Indian Ocean. It is currently extinct in th ...

) was sequenced in 2022, marking the first high quality skink reference genome.Dodge, Tristram O., Farquharson, Katherine A., Ford, Claire, et al. Genomes of two Extinct-in-the-Wild reptiles from Christmas Island reveal distinct evolutionary histories and conservation insights. ''Authorea.'' November 29, 2022. 10.22541/au.166974487.73559017/ Analysis of this genome revealed high genetic diversity, reflective of large historical population sizes. However, regions of the genome also showed signs of recent inbreeding, likely because skinks used to found the captive population were somewhat related.

Evolutionary relationships

''C. egeriae'' is most closely related to the ''metallicus'' group of ''

Cryptoblepharus ''Cryptoblepharus'' is a genus of skinks, lizards in the family Scincidae. The genus contains at least 53 species. Taxonomy The genus ''Cryptoblepharus'' was established in 1834 by the zoologist Arend Friedrich August Wiegmann. The type sp ...

,'' native to Australia, with the estimated divergence of ''C. egeriae'' from the group taking place around seven million years ago

References

{{Taxonbar, from=Q3005807 Cryptoblepharus Fauna of Christmas Island Reptiles described in 1888 Taxa named by George Albert Boulenger