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Escape behaviour often differs between sexes, reproductive states and ages. Escape theory predicts that flight initiation distance (FID = predator–prey distance when escape begins) increases as predation risk and fitness increase, and decreases as cost of escaping increases. Similar predictions hold for distance fled and refuge entry, suggesting that age and sex differences in escape behaviour may occur when risk, fitness, and opportunity costs differ. I studied such differences in two lizard species and reviewed relevant literature on escape by lizards. In Sceloporus virgatus no difference occurred between sexes or female reproductive states in FID, distance fled, distance from refuge, or probability of entering refuge. In S. jarrovii juveniles had shorter FID and distance fled than adults; juveniles were closer than females to refuge, but this did not affect FID or distance fled. Juveniles were more likely than adults to be on rocks and use them as refuges. The literature review showed that sexual dimorphism in FID occurs in about 1/5 of species (male FID usually > female FID), but distance fled differed between sexes in only 1 of 21 species. Juveniles had shorter FID than adults in all of five species; the relationship between age and distance fled was highly variable. Reasons for patterns of age/sex differences are discussed. Because age and sex differences in these factors and escape strategy can alter multiple components affecting optimality, sometimes in opposite ways, these factors and escape strategy must be known to predict effects of age, sex and reproductive state on escape.

1. The thermal relations of blue spiny lizards, Sceloporus cyanogenys, were studied in laboratory habitats which were designed to allow the expression of a large repertoire of natural behavior patterns. Body temperatures obtained with fast-reading thermometers and by radio telemetry from implanted transmitters were correlated with postures and activities. 2. The morning emergence of lizards was found to be cued by light, often in the absence of immediate thermal reinforcement. 3. Two basking postures which altered a lizard's air and substrate thermal interfaces could be distinguished. The environmental and body temperature correlates of these postures were not appreciably different, and the change from one posture to another could not be interpreted as thermoregulatory. 4. When thermal conditions permitted, basking continued up to the attainment of the maximum voluntary body temperature (38.7 C), and was then followed by perching. 5. The body temperature correlates of perching had a range and mean much like the "normal activity range" of other species of Sceloporus (28.2-38.7 C, X= 35.2). 6. Defecation occurred mostly in the morning towards the end of the basking period, but had a broad thermal range (27.5 to 35.7 C). 7. The range of body temperatures during feeding was broad (25.3-38.5 C), but that of foraging was much narrower (34.3-38.7 C).