The Black Rock Skink (Egernia saxatilis ) is a species of large skink native to Eastern and Southern Australia from central New South Wales to Grampians National Park in Victoria. A large, dark colored skink, up to 135 mm from snout to base of the tail, the Black Rock Skink is the first reptile discovered to have a "nuclear family" structure where the parents form a pair and care for their offspring for more than one year. The Black Rock Skink is a viviparous skink meaning females give birth to live offspring instead of laying eggs. They defend their home range and families against conspecifics for up to several years.
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TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
Oviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
Among animals, viviparity is the development of the embryo inside the body of the parent. The term 'viviparity' and its adjective form 'viviparous'...
Precocial species are those in which the young are relatively mature and mobile from the moment of birth or hatching. Precocial species are normall...
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MonogamyMonogamy is a form of relationship in which both the male and the female has only one partner. This pair may cohabitate in an area or territory for...
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starts withThe Black Rock Skink is a relatively large, mostly dark brown or black lizard with an average total length of 215 mm. The black upper side has a pattern of broken up pale scales that appear as white flecks. The scales on the back are keeled and rough to the touch, while the abdominal scales are smooth and not keeled. These ventral scales are also smaller than the dorsal scales. The underside of the skink is slightly orange and the ventral sides of the tail and throat are white with scattered black markings. The sides of the lizard have black scales with a scattering of lighter brown scales throughout. The feet and digits of the Black Rock Skink are black and shiny. The upper lip of the lizard is a lighter black color than the rest of the body. E. saxatilis reaches a maximum length of 140mm in snout to end of tail length.
E. saxatilis is diurnal and is the most active during the morning and later afternoon and spend the majority of their time sheltered in rock crevices. When the weather is warmer, they will emerge from these shelters to bask and forage.
The species is found in the southeastern woodlands of Australia, mainly on the coast and in nearby mountain ranges. They mainly inhabit the outcropping basalt bluffs of the Warrumbungle Ranges in New South Wales and the rocky outcroppings of the Great Dividing Range. E. s. saxatilis are found almost exclusively in the Warrumbungle Range, while E. s. intermedia are often found further east in the Great Dividing Range.
These skinks prefer permanent shelter for habitat including rock crevices beneath boulders and sometimes timber on rocky outcrops. Large crevices allow for a larger family to occupy them, however they are at higher risk of attack from predators including snakes. Permanent rock crevice habitats have different levels of quality depending on their level of sun exposure and their ability to offer thermoregulatory benefits to the lizards. They spend the majority of their time in and around these shelters. Basking and foraging all occurs within a close proximity to this permanent home. E. saxatilis saxatilis is exclusively rock-dwelling, whereas E. s. intermedia can be found in arboreal habitats. Egernia saxatilis can be excluded from timber habitats if related Egernia species are present, and forced to remain completely saxatile.
The social organization of these Australian lizards is very complex, as a study has shown monogamous tendencies among this species, contrary to the polygamous tendency of reptiles in general. The adults and young can stay together for over a year, with the female annually producing 2 - 3 young. They are viviparous. Based on examining similar species, it is thought that they can live for 10 years, and are mature by 2 - 3 years.
species, contrary to the polygamous tendency of reptiles in general. The adults and young can stay together for over a year, with the female annually producing 2 - 3 young. They are viviparous. Based on examining similar species, it is thought that they can live for 10 years, and are mature by 2 - 3 years.
Most Black Rock Skinks live in “nuclear family” systems, meaning a pair of parents lives with and protects their offspring. The vast majority of juveniles live in social groups and many of them live with their biological parents in a family group. Most of the groups that had at least two adults consisted of one adult male and one adult female.
For the juveniles and adults who do not live with their genetic relatives, the majority of them live in social groups. Juvenile lizards who are not in family groups are not forced into less preferable habitats though, in terms of thermoregulatory advantages. They inhabit the peripheries of family territories or occupy smaller crevices only suitable for one lizard.
Egernia saxatilis prey on invertebrates and are primarily insectivores. However, plants make up a significant amount of the diet in certain seasons of the year and for larger individuals. They eat mostly beetles, ants, cockroaches, and grasshoppers.
Egernia saxatilis is viviparous and gives birth to 1-4 young in late February to early March. Reproduction occurs annually.
Egernia saxatilis live in small families and adults defend their territories against conspecifics. The small “nuclear families” live in the same permanent shelter and the parents protect their infants from infanticidal conspecifics in this way.Long-term monogamy and group stability can be observed in the family groups. This is evident with up to three annual sibling cohorts living together with their biological parents at a time.
Adults attack unrelated juveniles but not their own offspring. The presence of a parent significantly reduces the rate of infanticide because conspecific adults ignore juveniles when a parent is present, likely because another adult is more threatening to the aggressive lizard. Therefore, a juvenile living within its parents’ own territory will experience far less attacks from conspecific adults.
Parents can provide their progeny better access to thermal resources and foraging opportunities. Increased opportunity to forage and bask leads to an increased growth rates and escape locomotion. Solitary juvenile lizards are at higher risk of infanticide because of their lack of parental protection and must take advantage of smaller crevices that adults and families would be unable to utilize. Males are more aggressive than females and win the aggressive interactions between the sexes. A female is unable to efficiently defend her young if attacked by a conspecific male and will often not confront them at all. The formation of family groups with a territorial male allows these paired males to protect juveniles from attacks by aggressive conspecific adult males.
The species is locally abundant, but distribution is severely fragmented and the number of adults appears to be decreasing. Egernia saxatilis was assessed by the NSW Threatened Species Committee, but there was not sufficient data to draw a clear conclusion on how threatened the species was, though due to the declining population, further investigation was suggested. The logging of eucalypts in southeastern Australia has caused a shift in the forest composition from a mixed population of young and old vegetation to an abundant amount of regrowing plants and trees. Lizards who require older and more sturdy trees to inhabit have been adversely affected. However, Egernia saxatilis is predominately a log-basking species and features of regrowth including thicker regenerating vegetation and high stem density prevent adequate sun exposure for these basking lizards. The absence of canopy openings in regrowing vegetation excludes E. saxatilis to the limited number of exposed logs clear of thick vegetation and in direct sunlight. Therefore, the deforestation in these areas forces these lizards out of their established habitats and requires them to look for a suitable habitat that becomes much more difficult to find with the regrowth process.
Social animals are those animals that interact highly with other animals, usually of their own species (conspecifics), to the point of having a rec...