Lizards do not typically construct architectural nests in the way birds do, but they engage in highly specific behaviors to secure a suitable environment for their offspring.
Where Most Lizards Deposit Eggs
The majority of lizard species are oviparous (egg-laying), but they generally do not construct complex structures. Instead, the female selects a deposition site based on two primary environmental factors: concealment and thermal stability. These sites must provide camouflage against predators while maintaining the temperature and humidity required for embryonic development.
Common deposition sites are typically found within existing natural features that offer stable microclimates. These include areas under rocks, inside the hollows of rotting logs, beneath leaf litter, or shallowly buried in soil or sand. Some species, such as certain geckos, may utilize the crevices of trees or caves, returning to the same spot repeatedly. This sometimes leads to communal egg-laying sites shared by multiple females. The female often performs a minimal excavation, digging a small hole with her snout or limbs before depositing the clutch and covering it up to hide the eggs from potential threats.
Oviparity Versus Viviparity
Lizard reproduction involves two strategies: oviparity and viviparity (live birth). While most species lay eggs, approximately 20% of all lizard species exhibit viviparity, where the young develop internally and are born as miniature versions of the adult.
Viviparity is prevalent in species that inhabit cooler climates, such as high altitudes or extreme latitudes. By retaining the developing embryos, the female lizard can behaviorally regulate the clutch temperature by basking in the sun or seeking shade. This protects the young from potentially lethal cold spells. Oviparous females must rely on the stable temperature and moisture conditions of the chosen deposition site.
Specialized Structures and Excavations
Although most lizards rely on passive hiding spots, some species exhibit specialized behaviors that involve significant environmental modification, bordering on true nest construction. These behaviors focus on creating an engineered chamber for incubation.
The common green iguana, for example, is known for its extensive nesting behavior. Females migrate long distances to suitable nesting grounds and use their limbs to excavate a deep nesting tunnel that can extend over a meter into the ground. At the end of this tunnel, she creates a chamber where she deposits a clutch of up to 50 eggs before filling the entire burrow with soil to conceal the entrance. This preparation ensures the eggs are kept at a stable temperature and humidity deep below the surface. These nesting sites are often communal, with multiple females returning to the same area year after year. Other exceptions include some species of Cyclura iguanas, which deposit their eggs inside subterranean sand chambers or within termite mounds, utilizing the insects’ structure for thermal stability.
Maternal Protection and Post-Hatching Care
Following egg deposition, the general pattern among lizards is abandonment; the female departs and provides no further parental investment. However, there are notable exceptions involving egg attendance and defense against predators.
In some species, such as the five-lined skink (Plestiodon fasciatus), the female remains with her eggs throughout the approximately six-week incubation period. She actively guards the clutch, sometimes coiling her body around the eggs to defend them from small predators. While post-hatching care is exceedingly rare, hatchling green iguanas have been observed engaging in social interactions and moving in small groups from communal nesting areas. This suggests a brief period of association that aids in early survival.