Multiple lizard species occupying the same retreat sites.
Robert A. Valentic and Grant Turner.
Valentic, R.A. & Turner, G. 1998. Herpetofauna 28(1): 40-43.
Observations of multiple species of reptiles and frogs occupying the same retreat are of interest because they represent examples of site-specific compatibility, indicate preferential retreat site selection, or the existence of a retreat site shortage in area. There have been numerous reports of Australian reptiles and frogs occupying the same retreat however only a few describe aggregations of more than one species (e.g., Bustard, 1970; Covacevich & Limpus, 1972, 1973; Cogger, 1973; Covacevich, 1974; Rankin, 1975; Maryan & Robinson, 1987; Valentic, 1993, 1996).
In this note we describe two separate occurrences of multiple lizard species occupying the same retreat. In both instances lizards occupied arboreal crevicollous retreats formed by decorticating bark around the bole of dead Eucalypt trees.
The observations occurred in June 1997 at two locations in northern New South Wales (NSW). Length measurements of lizards (snout-to-vent length: SVL; tail length: TL) were made using a rigid 500mm ruler. The sex of adult geckos was determined by an inspection of the ventral tail base: males were characterised by the presence of conspicuously swollen pouches (housing the hemipenes), and adjacent to these, caudal spurs; females lacked both of these features. The sex of adult skinks could not be reliably determined and therefore is not stated. Stage of maturity (i.e., adult, sub- adult, juvenile) are based on adult SVL’s given for each adult species in Cogger (1992). The relative positions of individuals on the tree bole were noted.
Location: Dandry Road approximately 4km in from the Newell Highway (31°09’S, 149°21’E), 19km north of the township of Coonabarabran, north-eastern NSW.
Habitat: ‘Pilliga scrub’ consisting of dense stands of Black Cypress-pine Callitris endlicheri, mixed Acacia spp. and Eucalypt forest (Narrow-leafed Ironbark Eucalyptus crebra, White Box E. albens, White Gum E. rossi) growing on a sandy, loam soil plain.
Date: 23rd June 1997. Time: 1450- 1505 hrs Eastern Standard Time (EST). Weather: Cool and sunny; max. 19° C.
Notes: A large dead Eucalyptus albens (diameter approx. 0.7m) beside a track was examined for the presence of reptiles. The main trunk of the tree was approx. 4 m in height, 2 m girth, with loose adherent bark 25-35mm thick. Charred portions of bark indicated that it had been burnt in the last few years. Bark was easily removed (and later reattached with nails) During this process three lizard species (10 individuals in total) were located on the bole of the tree. The bole itself was slightly moist and all lizards were attached to the bole rather than the bark. Details of the lizards are as follows: Tree Skink Egernia striolata - two adults (SVL 105mm (both) ; TL 91mm, 64mm (22mm of incomplete regeneration) and two juveniles (SVL 59, 58mm; TL 66, 53mm). Ocellated Velvet gecko Oedura monilis- two adults, a male (SVL 80mm; TL 64mm) and a female (SVL 80mm; TL 62mm, 51mm regen.complete). Eastern Spiny-tailed Gecko Strophurus williamsi- four adult specimens; two males (SVL 62, 59 mm, TL 37mm- 1mm of complete regeneration, 40mm) and two females (SVL 64, 66 mm, TL 40, 45 mm). Adult E. striolata and O. monilis were located at about the same height and within 0.3m of each other, while juveniles and S. williamsi were widely separated and at various heights.
Location: Pioneer Crossing, Gwydir River (29°25’S, 149°50’E), approximately 5km north of the township of Moree on the road to Mungindi, north-eastern NSW.
Habitat: Floodplain immediately adjacent to the Gwydir River consisting of open grassy woodland with River Red gum Eucalyptus camaldulensis and Box Eucalypts dominating on disturbed alluvial soils with a degraded grassy understory.
Date: 25th June 1997. Time: 1420 - 1510 hrs EST. Weather: Overcast with intermittent sunshine; max. 18° C.
Notes: A large dead River Red gum (diameter approx. 0.8 m) on a small slope some thirty metres from the rivers edge was examined. It was approx. 6 m tall with a 1.5 m girth, had flaking bark and was completely exposed. Beneath the bark were adult Ragged Snake-eyed Skinks Cryptoblepharus pannosus which were very active. Two adult Dtella Geckos Gehyra dubia were observed higher up. In between the two G. dubia was an adult Strophurus williamsi which was about 0.5 m from either. Individual details of lizards were not obtained in this instance. There were a number of other large River Red gums in the vicinity with flaking bark, all of which had numerous active C. pannosus on them.
While the importance of old or dead trees as roosting, nesting or shelter sites for birds and mammals is well known (Recher, 1984), there is much less known about their importance as refuges for arboreal species of reptiles. We found in each area that dead or mature trees with loose bark were used as refuges whereas younger trees that lacked crevices between the bole and the bark, or had very thin flaking bark, were rarely occupied. These ‘preferred’ refuges were uncommon at both localities and it seems that, in some instances at least, they take a considerable period of time to form. Senescent River Red gums, for example, are typically hundreds of years old. No reptiles were found on dead trees with flaking bark that were occupied by termites. Such trees were probably far less accessible to lizards due to the termites using soil to plug gaps between the bark and the bole. These observations concur with Bustard (1970) who stated the preferred habitat of Egernia striolata “….is free from dirt hence termites are habitat competitors”. The same would also seem to be true for the sympatric O. monilis and S. williamsi. Each lizard species was found to utilise other types of retreats within each habitat but in each instance occurred singly. Collectively these observations suggest that particular trees provide important habitat refuges for some lizard species.
A number of Egernia species are known to be gregarious, living in small ‘family’ groups (Greer, 1989; Ehmann, 1992; Hutchinson, 1993), and Bustard (1971) also found O. monilis to commonly occur in adult male- female pairs (this was observed above). Swanson (1987) states that E. striolata “…is usually found in family groups beneath loose bark of dead trees”. In contrast, Bustard’s (1970) study of Pilliga Scrub populations recorded adults occurring together on only five occasions (out of 250 sightings) and all occurred during the mating season in large home sites, however juveniles “quite frequently” occurred together with an immature or adult skink. Ehmann (1992: 242) notes that on smaller trees the species tends to be solitary but records a colony of eight on an “old, large River Red Gum“ suggesting that refuge size or availability may determine the occurrence of aggregations. We observed two further instances of cohabiting E. striolata near Uralla (30°38'S, 151°30'E) in the New England Tablelands of NSW: (i) a group comprising two adults and two juveniles and (ii) two adults (plus an adult Oedura tryoni) beneath weathered exfoliated granite. Additionally, on the lower slopes of Mt Korong (36°28'S, 143°45'E) in central Victoria; two adult, one sub-adult and three juvenile (juveniles of uniform size) E. striolata were observed cohabiting a small weathered granite exfoliation on an exposed granite dome with a north-easterly aspect in late May, 2008 (R. Valentic & Craig Stephenson, per. obs.). The latter exfoliation initially appeared too small to harbour the group found in occupancy. The timing of these observations does not coincide with the species’ known mating season (September-October, Bustard, 1970). Although few in number these observations suggest that associations between adult E. striolata are mediated by factors other than just mating.
We thank Glenn Shea for providing us with several important references and also the referees for their improvements to the manuscript.
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