Relocate nests/eggs for artificial incubation: Lizards
Overall effectiveness category Awaiting assessment
Number of studies: 15
Background information and definitions
Relocating eggs to artificially incubate them may be used as a way to maximise hatching success as the eggs will no longer be vulnerable to natural threats such as predation. Consideration must be given to the potential impacts of incubation conditions (for example temperature and humidity) on the sex, size, shape, colour, behaviour, movement ability and post-hatching growth of reptile hatchlings (Warner & Andrews 2002, Booth et al. 2006).
This action includes studies where eggs are incubated in artificial conditions, which ranges from controlled laboratory settings to using polystyrene boxes to incubate eggs in buildings. Studies are also included where gravid females are brought into captivity to lay eggs, but eggs are taken away from the females for artificial incubation.
Due to the number of studies found, this action has been split by species group, though no studies were found for amphisbaenians. See here for: Sea turtles; Tortoises, terrapins, side-necked & softshell turtles; Snakes; Crocodilians or Tuatara.
For studies that discuss the effects of relocating and re-burying eggs in natural habitats to avoid threats, see Relocate nests/eggs to a hatchery and Relocate nests/eggs to nearby natural setting (not including hatcheries).
Booth D.T. (2006) Influence of incubation temperature on hatchling phenotype in reptiles. Physiological and Biochemical Zoology, 79, 274–281.
Warner D.A. & Andrews R.M. (2002) Laboratory and field experiments identify sources of variation in phenotypes and survival of hatchling lizards. Biological Journal of the Linnean Society, 76, 105–124.
Supporting evidence from individual studies
A study in 1979 in the USA (Trautwein 1983) found that a wild-caught northern fence lizard Sceloporus undulatus hyacinthinus laid eggs that hatched successfully following artificial incubation in captivity. Two weeks after being brought into captivity, a female produced a clutch of 17 eggs. Sixteen of 17 eggs hatched successfully after an incubation period of 45 days. In 1979, a female lizard was captured and housed in a plywood box (3 x 4 x 1 feet) with 11 other northern fence lizards of varying sizes and sexes. The enclosures contained rocks and sand and temperatures ranged from 20–46°C. Eggs were moved to a plastic container with holes drilled in the bottom edge and placed in wet vermiculite. Incubation temperatures were 33–34°C for 20 days, and then varied between 20–29°C for the remainder of the incubation period.Study and other actions tested
A replicated, controlled study in 1990 in dry savanna in north-central Namibia (Phillips & Packard 1994) found that artificially incubated white-throated savanna monitor Varanus albigularis egg hatching success was almost double that of natural nests, although hatchlings were similar sized. Overall hatching success of artificially incubated savanna monitor eggs was 81% (120 of 148 eggs) compared to 47% (50 of 107 eggs) for natural nests (results not statistically tested). The average length of artificially incubated hatchlings was similar (115 mm) to hatchlings from natural nests (114 mm; results not statistically tested). Incubation time was longer and hatchlings were larger at lower incubation temperatures and in moister conditions (see original paper for details). In 1990, nine female monitors were radio-tracked through the breeding season. Five females were brought into captivity to lay eggs and four were monitored laying eggs in the wild. Captive-laid eggs were collected and incubated in mixed clutches in 27 boxes containing moistened vermiculite (15–17 eggs/box). Nine boxes contained high (-150 kPa), medium (-550 kPa), or low (-110 kPa) moisture levels. Three boxes of each moisture level were incubated at 27, 29 or 31°C. Artificially incubated (from 148 eggs) and natural-nest hatchlings (from 107 eggs) were checked and weighed on emergence.Study and other actions tested
A replicated, randomized, controlled study in 1997–1998 in Karnataka, southwest India (Radder et al. 2002) found that when eggs from wild-caught garden lizards Calotes versicolor were artificially incubated, hatching success was lower at higher incubation temperatures but was not affected by short exposures to high temperatures. Hatching success was lower at 35°C (33 of 59, 53%) and 33°C (36 of 61, 59%) than it was at 30°C (49 of 55, 89%) and at ambient temperatures of 27°C (138 of 148, 93%). Hatching success remained similar when eggs were exposed to short periods at 35°C (1 h/day: 15 of 16, 94%; 3 h/day: 14 of 15, 93%) compared to when eggs were incubated at ambient temperatures of 27°C (15 of 15, 100%). In 1997–1998, gravid female lizards were caught (number not given) and when they reached late gravidity eggs were removed from the oviduct (method not given). Eggs from 15 clutches were split between the treatment temperatures (55 eggs at 30°C, 61 at 33°C and 59 at 35°C) and ambient temperatures (148 eggs at 27°C). A further 46 eggs from three clutches were incubated at 27°C and exposed to 35°C for 1 h/day (16 eggs), 3 h/day (15 eggs) or kept at ambient temperatures (15 eggs). All eggs were incubated in black clay soil, and moisture levels were topped up every two days.Study and other actions tested
A replicated, randomized study in 1998 in Karnataka, southwest India (Radder et al. 2002) found that when eggs from wild-caught garden lizards Calotes versicolor were artificially incubated, eggs incubated in cotton wool had lower hatching success than those incubated in soil or sand. Hatching success was lower for eggs incubated in cotton wool (59 of 68, 84%) compared to those incubated in soil (59 of 61, 95%) or sand (84 of 87, 96%). Across all treatments, the average incubation period stayed the same (69 days), and three measures of hatchling size did not differ significantly (body mass, snout-vent length and tail length). In 1997–1998, gravid female lizards were caught (number not given) and when they reached late gravidity eggs were removed from the oviduct (method not given). In 1998, eggs from 15 clutches were incubated in either cotton wool (68 eggs), wet black clay soil (61 eggs) or sand (87 eggs). Eggs were incubated at ambient temperatures of 27°C. Every two days, moisture levels were topped up and new cotton wool was provided.Study and other actions tested
A replicated, randomized study in 1998–1999 in southern Spain (Díaz-Paniagua & Cuadrado 2003) found that during artificial incubation of common chameleon Chamaeleo chamaeleon eggs, hatching success, growth and survival were affected by temperature but not by moisture levels. Hatching success was higher at 25°C (100%) than at 29°C (53–76%) but was not affected by moisture levels (wet: 76–100%; dry: 53–100%). Similarly, hatchling survival during the first month was affected by incubation temperature but not moisture levels (result presented as statistical model), and growth was higher for hatchlings incubated at 25°C (0.19 mm/day) compared to those incubated at 29°C (0.09 mm/day). In 1998, ninety-six eggs from six wild nests were split evenly between 16 plastic boxes (6 eggs/box) and completely buried in moist vermiculite. Two temperature treatments (cool: 25°C; warm: 29°C) and two moisture treatments (wet: -150 kPa; dry: -600 kPa) were established, and four boxes each were assigned to each temperature-moisture treatment. All eggs were subjected to an initial low temperature period (<18°C) during November–February before temperatures were gradually increased to the treatment level.Study and other actions tested
A replicated, randomized study (years not provided) in laboratory conditions in New Zealand (Hare et al. 2004, same experimental set-up as Hare et al. 2008) found that lizard Oligosoma suteri hatchlings artificially incubated at 22–26°C survived significantly longer than those incubated at 18°C. Hatchlings incubated at 22°C and 26°C survived for longer (22°C: 94% of 50 survived 18 months; 26°C: 88% of 49 survived 18 months) than those incubated at 18°C (24% of 37 survived 18 months). See original paper for details on the effects of incubation temperature and moisture levels on body size and growth rates. Lizard eggs collected from wild females temporarily brought into captivity were randomly assigned incubation temperatures (18, 22 or 26°C) and moisture levels (–120 and –270 kPa). Eggs were artificially incubated in plastic containers with vermiculite (8–13 eggs/container and 2–4 containers/treatment). After hatching, juveniles were measured and housed in plastic-and-mesh containers for up to 18 months.Study and other actions tested
A replicated study in 2003 in an artificial setting in Zhejiang, China (Du et al. 2005) found that the hatching success of eggs and hatchling size from a species of Chinese skink Eumeces chinensis relocated for artificial incubation was not affected by fluctuations in incubation temperatures. At an average temperature of 27°C, hatching success was similar for eggs when incubation temperatures fluctuated by 3°C (12 of 15, 80%) or by 7°C (19 of 22, 86%). A range of hatchling traits, including size, weight and sprint speed were also similar when incubation temperatures fluctuated by 3°C or 7°C (see paper for details). In 2003, four gravid female skinks were brought into captivity and housed in an enclosure (110 x 90 x 50 cm) until they laid their eggs. Eggs were removed and clutches were split evenly between two incubation treatments: average temperature of 27°C with 3°C fluctuations (15 eggs); or average temperature of 27°C with 7°C fluctuations (22 eggs). Temperatures fluctuated gradually over a 24 h period. Hatching success was assessed and hatchling traits were measured (see paper for details).Study and other actions tested
A replicated, controlled study in 1998 in Cádiz province, southern Spain (Díaz-Paniagua 2007) found that artificially incubating common chameleon Chamaeleo chamaeleon eggs resulted in high hatching success, and that hatchling size was affected by the length of an initial cold period during incubation. Overall hatching success was 96%, with just one egg failing during the cold period of incubation (14°C) and two during the warm period (25°C). Hatchling length and body mass were affected by the length of the initial cold period of incubation (results presented as statistical model). In 1998, eggs were collected from seven chameleon nests (82 eggs, 10 or 12 eggs/nest) and incubated in sealed plastic boxes, completely buried in moist vermiculite. Eggs were initially incubated at 14°C for zero, 84, 119 or 149 days (cold period) and then kept at 25°C until hatching (warm period).Study and other actions tested
A replicated, randomized study (years not provided) in laboratory conditions in New Zealand (Hare et al. 2008, same experimental set-up as Hare et al. 2004) found that incubating lizards Oligosoma suteri at higher temperatures resulted in higher sprint speeds at higher ambient temperatures. At ambient temperatures of 26°C, lizards incubated at 22°C (0.8–0.9 m/s) and 26°C (0.9–1.0 m/s) sprinted faster than lizards incubated at 18°C (0.4–0.6 m/s). At temperatures of 18 and 22°C, lizards incubated at 18°C recorded speeds of 0.3–0.4 m/s, lizards incubated at 22°C recorded speeds of 0.6–0.7 m/s, and lizards incubated at 26°C recorded speeds of 0.6–0.8 m/s. The amount of water added to incubation substrate, lizard sex or size did not affect sprint speed (see original paper for details). Lizard eggs from 58 females were collected from the wild and randomly assigned to be incubated at 18 (20 lizards), 22 (49 lizards) and 26°C (48 lizards), at two water potential levels (-120 and -270 kPa). At 4–6 weeks and four months old, lizards were placed on an oval racetrack and encouraged to sprint using a paintbrush at three different ambient temperatures (18, 22 and 26°C). Lizards sprinted three times/ambient temperature. Maximum speeds were recorded and compared.Study and other actions tested
A study in 2005–2008 in laboratory conditions in Chiayi County, Taiwan (Norval et al. 2012) found that some wild female Kühne’s grass lizards Takydromus kuehnei laid eggs in captivity and following artificial incubation, more than half of the artificially incubated eggs hatched successfully. Five females laid a single clutch of 1–2 eggs (9 eggs total; numbers taken from table), and five of nine eggs (56%) hatched successfully. In 2005–2008, a total of 48 lizards were collected from the wild, 19 of which were classified as females. Lizards were housed temporarily (< 5 days) in small glass cages (25 x 25 x 27 cm) with a substrate of clean river sand overlain with sphagnum moss Sphagnum sp. Eggs were removed and placed in a small-animal cage on a substrate of clean river sand covered with sphagnum moss. Eggs were incubated at room temperature (25–32°C) and cages were misted to maintain a moist environment. Adult lizards were re-released in the same area they had been captured.Study and other actions tested
A replicated study in 2011 in laboratory conditions in Oklahoma, USA (Santoyo-Brito et al. 2012) found that some artificially incubated eggs from wild-caught, gravid female eastern collared lizards Crotaphytus collaris that laid eggs in captivity hatched successfully, but only eggs that were laid inside artificial nests hatched. All 17 wild-caught gravid female eastern collared lizards laid eggs in captivity (one clutch/individual, 5–9 eggs/clutch). Twelve lizards laid eggs inside artificial nest chambers (74 total eggs) and these eggs had a 62% hatching success after artificial incubation (46 of 74 eggs hatched). Five lizards laid eggs outside of artificial nest chambers (29 total eggs) and none of these eggs hatched after artificial incubation (23 eggs were desiccated when found after being laid and six eggs became mouldy during incubation). Seventeen gravid female lizards were caught in the Glass Mountains and moved to a laboratory where they were housed individually in partitioned wooden and metal-mesh cages. Each cage section (80 x 40 x 40 cm) contained gravel substrate, artificial lighting and an artificial nest made from bricks and sand/peat moss (see original paper for details). Lizards were fed and watered regularly. Eggs were moved for artificial incubation within 16 hours of being laid and adult lizards were returned to their capture site.Study and other actions tested
A replicated study in 2011 in Gansu, China (Tang et al. 2012) found that after bringing females of two species of toad-headed agamas Phrynocephalus przewalskii and Phrynocephalus versicolor into captivity to lay eggs, less than half artificial incubated eggs hatched successfully, and hatching success was lower at the highest incubation temperature. Hatching success was lowest at the highest incubation temperature for both species (Phrynocephalus przewalskii: 34°C: 32–36%; 26–30°C: 40–53%; Phrynocephalus versicolor: 34°C: 11–22%; 26–30°C: 52–76%), although this result was not statistically tested. Moisture content of the incubation medium had no effect on hatching success. Incubation period decreased at higher temperatures for both species (26°C: 44–46 days; 30°C: 31–33 days; 34°C: 23–26 days). In 2011, wild female lizards of both species were captured and housed in groups of 15 in cages (800 x 360 x 400 mm) with a sand substrate. Temperatures of 25–37°C were available during the day and were 20°C at night. Eggs were collected (Phrynocephalus przewalskii: 263 eggs from 101 females; Phrynocephalus versicolor: 185 eggs from 66 females) and assigned to three temperature (26, 30, 34°C) and two moisture level (2 g water/5 g vermiculite, 2 g water/8 g vermiculite) treatments. Eggs were incubated in plastic containers (150 ml).Study and other actions tested
A replicated study in 2010–2011 in Gansu and Zhejiang provinces, China (Wang et al. 2013) found that after bringing wild, gravid females of five Phrynocephalus species into captivity, some artificially incubated eggs hatched successfully. Data on hatching success is not provided. Incubation period was shorter at higher temperatures for all species (24°C: 44–56 days; 28°C: 32–38 days: 32°C: 26–28 days), and none of seven measures of hatchling size were affected by temperature (results presented as statistical model). In 2010–2011, gravid females of five species were collected and housed in cages (900 x 650 x 600 mm) in groups of 7–10 individuals of the same species. A substrate of sand, and clay tiles were provided, and temperatures were 20–28°C. Females were moved to individual cages (200 x 200 x 200 mm) to lay eggs. Eggs were incubated at 24°C (54 eggs), 28°C (44 eggs) or 32°C (59 eggs) in individual covered jars (50 ml) in vermiculite (1:1 with water by weight). Adult females were released back in to the wild after 3–4 months.Study and other actions tested
A replicated, randomized study in 2010–2011 in laboratory conditions in Zhejiang province, China (Shen et al. 2017) found that most eggs laid in captivity by wild Chinese skinks Plestiodon chinensis and artificially incubated hatched successfully, and hatching success was not affected by incubation temperature. Overall hatching success was 86% (837 of 972 eggs) and was similar at all incubation temperatures (83–86%). In addition, incubation period decreased at higher temperatures (40 days at 24°C vs 19 days at 32°C). In 2010–2011, seventy-two gravid females were brought into captivity and housed in groups of 5–8 in enclosures (1.5 x 1.5 x 0.6 m) with a turf-covered substrate. A total of 972 viable eggs were collected and placed in individual plastic jars (50 ml) with moist vermiculite (-12 kPa). Clutches of eggs were divided between five constant temperature treatments (24, 26, 28, 30 or 32°C) or one fluctuating treatment (incubated outside). After laying, adult females were re-released at their point of capture.Study and other actions tested
A replicated, randomized study in 2013–2015 in south China (Ma et al. 2018) found that artificially incubating forest skink Sphenomorphus incognitus eggs at different temperatures did not affect hatching success or hatchling morphology, but that higher temperatures resulted in shorter incubation periods. Hatching success did not change significantly at different incubation temperatures (69% at 22°C; 77% at 25°C; 82 % at 28°C) or when incubation temperature fluctuated around an average of 25°C (3°C fluctuation: 79%; 5°C fluctuation: 64%). Five measures of morphology were also similar at different incubation temperatures (see paper for details). Average incubation period varied between 76 days at 22°C and 40 days at 28°C. In 2013–2015, twenty-seven wild, gravid female skinks were collected and housed in individual plastic cages (540 x 400 x 320 mm) with a substrate of moist soil at 20–28°C. A total of 136 eggs were incubated in individual, covered plastic jars (50 ml) with moist vermiculite. Eggs from each clutch were divided equally between three constant temperature treatments (13 eggs at 22°C, 26 at 25°C, 11 at 28°C) and two treatments that fluctuated around an average of 25°C (28 eggs at 3°C fluctuation, 25 at 5°C fluctuation).Study and other actions tested