Maintain wild-caught, gravid females in captivity during gestation

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Seven studies evaluated the effects on reptile populations of maintaining wild-caught, gravid females in captivity during gestation. Two studies were in the USA and New Zealand and one was in each of Japan, Iran and Mexico.



  • Reproductive success (7 studies): Five replicated studies in the USA, Japan, Iran and Mexico found that varying numbers of wild-caught snakes and lizards gave birth to live young or laid eggs that hatched successfully in captivity. One study also found that eggs laid in artificial nest chambers had higher hatching success than those laid outside of the chambers. One study in New Zealand found mixed effects of providing different basking conditions on the number of McCann’s skinks and common geckos that gave birth successfully. One controlled study in New Zealand found that McCann’s skinks in captivity that were treated for mites completed pregnancy more often and produced more viable offspring compared to skinks not treated.


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated study in 1995–2001 in a captive setting in Illinois, USA (King & Stanford 2006) found that gravid plains gartersnakes Thamnophis radix maintained in captivity produced some live offspring. From 38 litters, 473 offspring were alive (79%) and 128 were stillborn (21%). From 18 litters obtained by inducing females with oxytocin, 343 offspring were alive (67%) and 112 stillborn (33%). In 1995–2001, gravid females were captured (number not given) and maintained in captivity in individual glass aquaria (40 l) until giving birth. The room was kept at 24–26°C (32°C at one end of aquarium) and humidity at 50%.

    Study and other actions tested
  2. A study in 2005–2008 in rocky grassland and laboratory conditions in South Island, New Zealand (Cree & Hare 2010) found that most wild pregnant McCann’s skinks Oligosoma maccanni and common geckos Hoplodactylus maculatus kept in captivity gave birth, although gestation success in skinks depended on the basking regime that they were exposed to in captivity. Female McCann’s skinks exposed to basking temperatures for 3.5 days/week had lower gestation success (53% success) than skinks exposed to basking temperatures for 5 or 7 days/week (78–83% success). Similar numbers of female common geckos developed at least one viable offspring regardless of basking regime (3.5 days/week: 80% success; 5 days/week: 90% success; 7 days/week: 80% success). Most geckos that developed full-term embryos required inducement (see original paper for details). Clutch sizes were similar between different basking regimes for both skinks and geckos (see original paper for details). Pregnant female McCann’s skinks and common geckos were collected from the wild in November 2005 and October 2007 and kept in one of three basking regimes, with heat provided for: 8 hours/day for 3.5 days/week (17 skinks, 10 geckos), 5 days/week (18 skinks, 10 geckos) or 7 days/week (23 skinks, 10 geckos). Lizards were monitored until they gave birth and some lizards were induced when over-gestation was apparent using the hormone arginine vasotocin (see original paper for details). Gestation was considered a success when at least one viable offspring was delivered.

    Study and other actions tested
  3. A controlled study in 2004 and 2007 in laboratory conditions in South Island, New Zealand (Hare et al. 2010) found that wild-caught pregnant female McCann’s skinks Oligosoma maccanni gave birth in captivity, but pregnancy success and offspring viability was improved when skinks were treated for mites. When mites were treated with vegetable oil, the majority of wild-caught pregnant female McCann’s skinks gave birth successfully (22 of 30 skinks completed pregnancy successfully, 2 of 30 skinks had partially successful pregnancies), whereas when mites were not treated, most pregnancies were not successful (1 of 17 skinks had a partially successful pregnancy). Female McCann’s skinks treated for mites produced more viable offspring (2.6 offspring/female), compared to when mites were not treated (0.1 offspring/female). Two weeks after initial treatment with oil, 14 of 30 female skinks showed signs of mites still being present. After 28 days (and two treatments of oil), no live mites were observed. In October 2004 and 2007, pregnant female McCann’s skinks were taken from the wild and maintained in controlled temperature and lighting conditions in individual containers (2004: 17 individuals; 2007: 30 individuals; see original paper for details). In 2004, all skinks had scale mites and were not treated. In 2007, all skinks were treated for mites using sunflower oil following capture. Skinks were checked for mites and retreated with oil as necessary on the 14th day (all skinks oiled), 28th day (only those skinks with raised scales were re-oiled) and 56th day (no skinks were re-oiled) following capture.

    Study and other actions tested
  4. A replicated study in 2007 in Japan (Kadota et al. 2011) found that wild-caught, gravid female pit vipers Ovophis okinavensis that were maintained in captivity laid eggs that hatched successfully. Authors report that 22 eggs from seven clutches hatched successfully. In 2007, six gravid female snakes were brought into captivity and housed individually in plastic cages. Eggs were temporarily removed for measuring and then returned to the cage to incubate with the female.

    Study and other actions tested
  5. A replicated study 2008–2009 in Tehran, Iran (Kian et al. 2011) found that two of nine wild-caught, gravid Latifi's vipers Montivipera latifii gave birth to live young in captivity. In 2008, one female produced a single live young snake, while seven other females produced only stillborn young or infertile egg masses. In 2009, one gravid female produced a litter of 10 live young. In 2008–2009, a total of 26 wild vipers, including nine gravid females, were captured and housed in vivaria of various sizes. Peat moss was provided as a substrate, along with broken flowerpots for cover. Temperatures range from 30–32°C under a heat lamp and 26–28°C elsewhere in the enclosure, and humidity averaged 40–50%.

    Study and other actions tested
  6. A replicated study in 2011 in laboratory conditions in Oklahoma, USA (Santoyo-Brito et al. 2012) found that all wild gravid female eastern collared lizards Crotaphytus collaris brought into captivity laid eggs, but that only eggs 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 (46 of 74 eggs hatched). Five lizards laid eggs outside of artificial nest chambers (29 total eggs) and none of these eggs hatched (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
  7. A replicated study in 1991–2004 in laboratory conditions in the State of Mexico, Mexico (Manjarrez & San-Roman-Apolonio 2015) found that wild-caught, gravid Mexican garter snakes Thamnophis eques and blackbelly garter snakes Thamnophis melanogaster successfully gave birth to live offspring in captivity. Mexican garters produced 275 live offspring and 13 dead offspring from 21 litters, and blackbelly garters produced 325 live, and 15 dead offspring from 43 litters. The sex ratio for Mexican garters was even (125 males, 146 females, and 4 unsexed), whereas blackbelly garters produced more than twice as many female as male offspring (99 males and 226 females). In 1991–2004, twenty Mexican garter snakes and 43 blackbelly garter snakes that were found to be gravid (by palpating for presence of embryos) were brought into captivity. Snakes were maintained in individual terraria with a paper substrate and a water bowl. Temperatures ranged from 20–25°C. Two to three weeks after birth, adult snakes and their offspring were released where they had been captured.

    Study and other actions tested
Please cite as:

Sainsbury K.A., Morgan W.H., Watson M., Rotem G., Bouskila A., Smith R.K. & Sutherland W.J. (2021) Reptile Conservation: Global Evidence for the Effects of Interventions for reptiles. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

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