The behavioural response of the sleepy lizard Tiliqua rugosa to an extended drought was examined in spring and summer 2002. Observations of the behaviour and use of microhabitat by radio-tagged lizards for spring in 2000–2002 showed that the lizards in 2002 suffered decreased body mass and increased mortality, were less active, showed reduced mating behaviour and increased use of burrows when compared with the more normal wetter years of 2000 and 2001. The lizards lost significant mass owing to dehydration and starvation. An ‘onboard’ data logger recorded lizard stride frequency and body temperature continuously for 4 months on 11 lizards during the drought of 2002. The normally diurnal heliothermic sleepy lizards responded to rare rainfall events during the drought whenever they occurred, day or night, by emerging from burrows or other shelters for extended periods of activity with sub-optimal body temperatures as low as 8.5 °C. They moved more often, and with higher stride frequencies during periods of rain than during dry periods, both overnight and during the day. As a consequence of this extended activity under physiological stress, the lizards were able to respond to naturally occurring transient opportunities for food and water that would not have been available if they were only active at optimal body temperatures. In an area where freestanding water is rarely available, the lizards were able to access limited water by licking substrate. They also gained water and perhaps nutrition by consuming the temporarily rehydrated thalli of the free-living terrestrial cyanobacterium Nostoc commune. Such behaviour enabled lizards to regain much of the mass lost before the rainfall and probably enabled many lizards to survive until more normal food sources became available. These rare events may have a significant effect on the shaping of the sleepy lizards phenotypic capacities outside routine day-to-day activities.

The Australian sleepy lizard Tiliqua rugosa forms socially monogamous pair bonds for 6 to 8 weeks each spring before mating occurs. This behaviour could not be explained by any hypothesis involving males helping to rear their young, because pairs split up soon after mating, and males seem to have no contact with the offspring of their partners. Short monogamous associations in other lizard species are often interpreted as mate guarding by the male to assure paternity. The mate guarding hypothesis was tested by experimental separation of pairs at various times during the pairing season. Data from 73 trials indicated that males were more likely to return to females than vice versa, and that the tendency of males to return to females increased as the time of mating approached. Also, reunion was more likely in pairs that had a greater tendency to remain together during the season. These results are consistent with predictions that the monogamous relationship is a form of mate guarding by males. However, the incidence of females re-uniting with males, and the long duration of pair bonds before mating occurs are not predicted by a mate guarding hypothesis. There may be additional explanations for monogamous pairing in the sleepy lizard.

Over 15 years (1983–97) 25 665 random encounter captures of adult sleepy lizards, Tiliqua rugosa, were made at a site near Mt Mary, in the mid-north of South Australia. The last months of winter (July and August) became warmer and drier in the later years of the study, and the spring months when lizard activity was highest (September and October) had increased rainfall. The lizards form monogamous pairs for an average of 8 weeks before mating in late October or early November. Pairing started earlier and lasted longer in later years of the study. The time when pairing ended showed no significant temporal trend, although it was earlier in years with warmer spring temperatures. These results suggest that the timing of reproductive behaviour was influenced by climatic variation.

Sleepy lizards Tiliqua rugosa are large, long-lived, Australian skinks that live in stable home ranges. Previous studies showed that the lizards have a good sense of orientation and navigation towards home. However, since they are active only 4 months in every year, there is a question about which environmental cues enable them to locate their home boundaries. In the present study we determined whether surrounding olfactory and chemical cues are important for the sleepy lizards for home-range maintenance. In the first part of the study we showed in the laboratory that zinc sulphate (ZnSO4) is a chemical that induces anosmia and prevents detection of chemical cues in sleepy lizards for up to 30 days, with no evident long-term harm to the animals. We then monitored the location of 50 radio-tagged sleepy lizards. After determining their home ranges they were divided into three groups: an untreated control, a saline-treated (sham-operated) group and a ZnSO4-treated group. Starting 2 days after the treatment, the home ranges of all lizards were re-determined within the period that ZnSO4 blocked olfaction. Three variables were calculated comparing home ranges before and after treatments: the change in home-range size, the distance between the centre of activities of the lizards, and the overlap between the individual home ranges before and after treatments. Lizard home ranges varied from 1.9 ± 0.6 ha to 4.6 ± 1.4 ha before treatment, and 1.3 ± 0.3 ha to 3.1 ± 0.7 ha after treatment. There was no significant effect of treatments or of sex on the home-range size or on the distances between the centre of activities, or on the overlap between the individual home ranges. Our data indicate that olfaction and vomerolfaction are not a major cue for home-range maintenance in the sleepy lizards.