Relocate nests/eggs for artificial incubation: Tortoises, terrapins, side-necked & softshell turtles
Overall effectiveness category Awaiting assessment
Number of studies: 17
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.
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 a 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 replicated study in 1966–1971 in an artificial incubating facility in Galápagos, Ecuador (MacFarland et al. 1974) found that eggs from five subspecies of Galápagos giant tortoise hatched successfully after artificial incubation. Results were not statistically tested. Hatching success of artificially incubated Geochelone elephantopus ephippium eggs was 51% (158 of 312 eggs), G. e. darwini eggs was 37% (44 of 118 eggs hatched, 83 embryos died, 71 infertile eggs), G. e. hoodensis eggs was 63% (20 of 32 eggs hatched, 28 embryos died, 46 infertile eggs), G. e. porteri eggs was 35% (6 of 17 eggs hatched, 11 eggs infertile), and G. e. chathamensis eggs was 100% (3 of 3 eggs hatched). Hatching success of G. e. ephippium and G. e. porteri eggs incubated in undisturbed natural nests in the wild was 82% (103 of 133 eggs hatched, 4 embyros died, 18 infertile eggs) and 76% (391 of 520 eggs hatched, 21 embryos died, 101 infertile eggs) respectively. In the 1969/1970–1970/1971 nesting seasons, giant tortoise eggs laid by G. e. ephippium (312 total eggs), G. e. darwini (118 total eggs), G. e. hoodensis (32 total eggs), G. e. porteri (17 total eggs) and G. e. chathamensis (3 total eggs) were transported to an artificial incubation facility (1–2 hours on foot and 5–6 hours by boat). Eggs were incubated in wooden boxes with a soil substrate (see original paper). Hatching success and egg fertility was compared between subspecies and to naturally incubated, undisturbed G. e. ephippium and G. e. porteri eggs laid in the same seasons.Study and other actions tested
A replicated study in 1969–1971 in an artificial incubating facility in Galápagos, Ecuador (MacFarland et al. 1974) reported that Galápagos giant tortoise Geochelone elephantopus ephippium egg hatching success was higher when eggs were left longer in natural nests before being relocated for artificial incubation. Results were not statistically tested. Of artificially incubated giant tortoise eggs, 74% (43 of 71) moved at 10–15 weeks, 67% (4 of 6) moved at 7–9 weeks, 19% (5 of 29) moved at 4–6 weeks, and 19% (5 of 27) moved at 0–2 weeks hatched successfully. In undisturbed natural nests, 82% (103 of 133) of G. e. ephippium eggs and 76% (391 of 520) G. e. porteri eggs hatched. In the 1969/1970 and 1970/1971 nesting seasons, giant tortoise eggs were transported at 10–15 weeks (71 eggs from 16 clutches), 7–9 weeks (6 eggs from 2 clutches), 4–6 weeks (29 eggs from 6 clutches) and 0–2 weeks (27 eggs from 5 clutches) after laying to an artificial incubation facility. Eggs were incubated in wooden boxes with a soil substrate (see original paper). Hatching success was compared to clutches left undisturbed laid by G. e. ephippium (133 eggs from 26 clutches) and G. e. porteri (520 eggs from 55 clutches) in the same nesting seasons.Study and other actions tested
A study in 1985–1986 at Columbus Zoo, Ohio, USA (Goode 1988) found that two of three incubated eggs laid in captivity by a wild-caught gravid gibba turtle Mesoclemmys gibba hatched successfully. A female laid three eggs over a one-month period, and two hatched successfully after 154 and 164 days of incubation. The third egg failed during incubation. A wild-caught female was acquired in 1985 and housed along with a range of other turtle species in a 140 cm square display tank, with 50 cm deep water and a basking spot. Water temperature was 20–24°C and air temperatures were 24–32°C. Eggs were incubated at 26–31°C in sealed 1 gallon jars in a 1:1 mixture of vermiculite and water (by weight), and jars were vented every 4–6 weeks.Study and other actions tested
A replicated study in a laboratory in Illinois, USA (Tucker 1995) found that after incubating eggs recovered from road-killed red-eared sliders Trachemys scripta elegans, more than half of the eggs hatched successfully, and hatching success was higher for eggs from turtles found with intact carapaces compared to those with open carapaces. Forty-three of 67 (64%) eggs hatched successfully. Hatching success was higher for eggs recovered from turtles with intact shells (30 of 35, 86 %) compared to those with shells that had been opened (13 of 32, 41 %). Of 32 turtles that were found on a road having been hit by a vehicle, nine contained 2–21 unbroken eggs. One turtle survived and was later released after laying eggs. Unbroken eggs were transferred to a laboratory and partially buried in perlite incubation medium in plastic containers (32 x 19 x 10 cm), with aluminium foil layered under the lid. Clutches were incubated separately. A road was searched for turtles hit by vehicles at least twice daily during the nesting season (months not given).Study and other actions tested
A replicated study in 1992 in Pennsylvania, USA (Ewert et al. 2002) found that most artificially incubated pond slider Trachemys scripta and Mississippi map turtle Graptemys pseudogeographica kohni eggs hatched successfully, but higher CO2 concentrations during incubation led to lower hatching success for pond sliders in two of three comparisons and a higher proportion of female hatchlings for both species. Compared to 0% CO2, hatching success was lower at the highest concentration of CO2 for pond sliders (24 of 25 eggs at 0% CO2 vs 4 of 25 at 15% CO2; all with 21% oxygen), but remained similar at medium CO2 concentrations for both species (pond sliders: 21 of 25 at 10% CO2; map turtles: 12 of 14 at 0% CO2 vs 7 of 14 at 10% CO2; all with 21% oxygen). The proportion of males to females was lower at higher concentrations of CO2 for pond sliders (0%: 22:2; 10%: 11:12; 15%: 4:6) and map turtles (0%: 10:2; 10%: 3:6). A separate trial for pond slider eggs at high CO2 (15%) and 10% oxygen resulted in 0 of 24 eggs hatching successfully and a sex ratio of one male to six female embryos. In 1992, gravid, wild female turtles were injected with oxytocin to obtain their eggs. Groups of 25 pond slider eggs were incubated at 0, 10 or 15% CO2, and groups of 14 map turtle eggs were incubated at 0 or 10% CO2, all with 21% oxygen. A further 24 pond slider eggs were assigned to a treatment involving high CO2 (15%) and reduced oxygen levels (10%).Study and other actions tested
A replicated, randomized study in 2001 in a laboratory setting in Hangzhou, China (Du et al. 2006) found that artificially incubating Chinese three-keeled pond turtle Chinemys reevesii eggs at different temperatures did not influence hatching success, but did influence four of five measure of hatchling size and six of 16 comparisons of locomotor performance. Hatching success was similar across all incubation temperatures (73–96%). Four of five measures of hatchling size were affected by temperature (see paper for details). Locomotor performance (four measures of swimming and crawling performance) was better for hatchlings incubated at 27 and 30°C in six of 16 comparisons and similar in the remaining 10 comparisons compared to those incubated at 24 and 33°C. In July 2001, a total of 111 viable eggs (from a private hatchery) were incubated in plastic boxes in moist vermiculite at 24°C (24 eggs), 27°C (28 eggs), 30°C (28 eggs) or 33°C (30 eggs). Crawling and swimming performance of hatchlings was assessed by chasing them along a “racetrack” covered with sand (crawling) or 50 mm of water (swimming).Study and other actions tested
A randomized study in laboratory conditions in Indiana University, Kokomo, USA (Finkler 2006) found that snapping turtle Chelydra serpentine eggs artificial incubated in substrate with higher moisture levels had higher hatching success up to a threshold, after which hatching success was lower. Snapping turtle eggs artificially incubated in 9% and 7% soil moisture had the highest hatching success (7%: 14 of 20 eggs hatched; 9% 16 of 20 eggs hatched) compared to lower soil moisture levels (3%: 9 of 20; 5%: 10 of 20 eggs hatched) or higher soil moisture levels (11%: 9 of 20; 12% 8 of 20 eggs hatched). Survivorship of hatchlings was significantly lower in at 13% moisture level compared to 7% or 9% moisture level (data presented as statistical model outputs). Freshly laid eggs were collected from the wild in June 2002 (120 total eggs from six clutches). Eggs were incubated under one of six soil moisture conditions: 3, 5, 7, 9, 11, and 13% water content (two nest boxes of 10 eggs/moisture level). Eggs were buried to 3 cm depth in the soil and incubated at 25°C.Study and other actions tested
A replicated study in 1978–2006 in a laboratory in the USA (Feldman 2007) found that when eastern painted turtle Chrysemys picta picta eggs from natural nests and from turtles induced with oxytocin were artificially incubated, most hatched successfully. Fifty-seven of 62 (92%) of oxytocin-induced eggs and 58 of 60 (97%) natural nest eggs hatched successfully, and there was no difference in the hatching success or incubation period (average of 58 days) between oxytocin-induced and natural eggs. Sixty painted turtle eggs were collected from eight wild nests, and 14 turtles were collected before laying and induced with oxytocin, yielding 62 eggs. All eggs were incubated in a 50:50 mix by weight of vermiculite and water. Oxytocin (1.4–2.5 units/100 g) was injected into each turtle using a syringe.Study and other actions tested
A study in 2005–2006 in man-made sandbar habitat in Arkansas, USA (Plummer 2007) found that most smooth softshell turtle Apalone mutica nests moved to an outdoor enclosure for incubation hatched. In total, 314 hatchlings emerged from 26 clutches over two nesting seasons. Fourteen eggs from seven clutches did not hatch and two hatchlings died soon after hatching. Turtle eggs were collected from natural nests in May-June 2005–2006 and reburied in an outdoor enclosure in a laboratory facility (2005: 12 eggs each from 10 clutches; 2006: 10–21 eggs each from 16 clutches). The nesting area was monitored twice daily and videoed continuously in the last predicted week prior to hatching.Study and other actions tested
A replicated, randomized, controlled study in 2004–2005 on one grassy bank of a river delta in Rio Grande do Sul state, Brazil (Bujes & Varrastro 2009) found that artificially incubating Hilaire’s side-necked turtle Phrynops hilarii eggs resulted in higher hatching success and larger hatchlings compared to eggs incubated in natural nests. Hatching success was higher for artificially incubated eggs (hatching success/nest 50–100%, 25 of 28 eggs hatched) compared to eggs from natural nests (hatching success/nest 43–75%, 30 of 50 eggs hatched), though this result was not tested statistically. Hatchlings from artificially incubated nests were heavier than those from natural nests (artificial: 14 g; natural: 9 g), and larger in four of five measures (see paper for details). In September 2004, six natural turtle nests were selected and 40% of eggs were removed for artificial incubation (28 eggs), and the rest left in place (50 eggs). Natural nests were covered with a plastic screen. Removed eggs were placed in cooler boxes (1,000 x 400 x 350 mm) in moist vermiculite (2:1 ratio with water by volume), and additional water was added whenever the vermiculite was dry. Hatchlings were counted, weighed and released at the nesting site two weeks after hatching.Study and other actions tested
A replicated, controlled study in 2009 on two rivers in Southern Venezuela (Herández et al. 2010) found that artificially incubating eggs of yellow-headed sideneck turtles Podocnemis unifilis resulted in lower hatching success compared to eggs moved to an on-beach hatchery and eggs from natural nests. Results were not statistically tested. Hatching success was lower for artificially incubated eggs (42%) than for eggs from both the on-beach hatchery (88%) and natural nests (63%). Eggs that were artificially incubated came from locations where all eggs from a further 74 nests had been harvested by people. All eggs from 13 nests (401 total) at one river were placed in sand-filled polystyrene containers and incubated indoors in ambient conditions. Five eggs each from 27 nests (136 total) at the second river were moved to a hatchery and reburied in a trench (200 x 40 x 30 cm) using sand from the nesting site. The area was protected by a 1.5 m metal mesh fence, and two staff monitored the site and poured 5 litres of water over the trench each week. All eggs from a further 51 nests from the second river were left in place. In February 2009, a six and 13 km stretch of each river was searched for nests. In May, these locations were revisited to assess hatching successStudy and other actions tested
Referenced paperHerández O., Espinosa-Blanco A.S., May Lugo C., Jimenez-Oraa M. & Seijas A.E. (2010) Artificial incubation of yellow-headed sideneck turtle Podocnemis unifilis eggs to reduce losses to flooding and predation, Cojedes and Manapire Rivers, southern Venezuela. Conservation Evidence, 7, 100-105.
A replicated study in 2009 in an artificial setting in Zhejiang, China (Chen et al. 2011) found that some Asian yellow pond turtle Mauremys mutica relocated for artificial incubation hatched successfully, and that higher incubation temperatures resulted in higher growth rates for hatchlings from one of two populations. Overall, 19 of 35 (54%) clutches of artificially incubated eggs hatched successfully (2 eggs/clutch; one incubated at 26°C and one at 30°C). Growth rate of hatchlings sourced from a more southerly population was lower for those incubated at 26°C (0.06 g/day) compared to those incubated at 30°C (0.1 g/day), whereas hatchlings from a more northerly population grew at similar rates at both incubation temperatures (0.04–0.05 g/day). Initial hatchling mass was similar for those incubated at 26°C (5–6 g) and those incubated at 30°C (5–6 g). In 2009, fifteen clutches of eggs were collected from a more southerly wild population (Hainan province) and 20 clutches were collected from a more northerly population (Zhejiang province). Eggs were individually incubated in jars with moist vermiculite, and one egg from each clutch was incubated at 26°C and one was incubated at 30°C. Hatchlings were weighed soon after emergence and then maintained at 28°C for 90 days and weighed again to measure growth rate.Study and other actions tested
A replicated study in 2011–2012 in Phra Nakhon Si Ayutthaya province, Thailand (Pewphong et al. 2013) found that artificially incubating snail-eating turtle Malayemys macrocephala eggs at higher temperatures resulted in more physical deformities in embryos. Higher incubation temperatures resulted in more embryos having physical deformities (1% at 26°C; 3% at 29°C; 30% at 32°C). The proportion of infertile eggs did not differ between the temperature treatments (8% at 26°C; 4% at 29°C; 11% at 32°C). In 2011–2012, a total of 712 eggs from 126 wild turtle nests were collected. Eggs were placed in plastic boxes containing moist vermiculite (1:1 ratio with distilled water) and incubated at 26°C (237 eggs), 29°C (237 eggs) or 32°C (238 eggs). Eggs were randomly selected for dissection each week to assess embryos for developmental abnormalities. Embryos were euthanised with an injection of sodium pentobarbital (600 mg/kg).Study and other actions tested
A replicated study in 2010 in pine forest and artificial conditions in Mississippi, USA (Holbrook et al. 2015) found that less than half of artificially incubated gopher tortoise Gopherus polyphemus eggs collected from two sites hatched successfully in captivity. Fourteen of 46 (30%) artificially incubated gopher tortoise eggs collected from one site and 22 of 47 (47%) artificially incubated gopher tortoise eggs collected from a second site hatched successfully in captivity. Three hatchlings died within three days of emerging and one never gained function of its rear legs. Ninety-three gopher tortoise eggs were collected from two sites within 24 hours of deposition in May–June 2010 and relocated for artificial incubation. Eggs were placed in dampened vermiculite (0.7 g water to 1.0 g vermiculite) in individual sterilized containers and incubated at 29.3°C. Eggs were collected as part of a head-start programme.Study and other actions tested
A replicated study in 1994–1999 in New York State, USA (Michell & Michell 2015) found that most wood turtle Glyptemys insculpta eggs collected from the wild and artificially incubated hatched successfully. In total, 15 of 18 (83%) artificially incubated wood turtle eggs hatched successfully (1994: 8 of 10 eggs; 1998: 3 of 3 eggs; 1999: 4 of 5 eggs). Wood turtle eggs were collected from wild nests in 1994 (10 eggs), 1998 (3 eggs) and 1999 (5 eggs). The authors noted that eggs were collected from nests that would otherwise have failed. Eggs were placed in dampened vermiculite (1:1 vermiculite: water by weight) and lightly covered with vermiculite in an airtight container, which was opened once a week, until hatching.Study and other actions tested
A replicated, controlled study in 1974–2012 in a laboratory and 11 wetland sites in New Jersey and Pennsylvania, USA (Zappalorti et al. 2017) found that bog turtle Glyptemys muhlenbergii eggs incubated in a laboratory had higher hatching success than eggs left in wild nests. Hatching success was higher for eggs in the laboratory (74 of 91, 81% [numbers taken from table]) than for eggs in wild nests (caged nests: 42 of 97, 43%; uncaged nests: 53 of 161, 33%). Average hatching date was similar in the laboratory and field (30–31st August). Eggs were transferred from nests to a laboratory and incubated in plastic containers with humus from the wetland. Incubation temperatures ranged from 26–32°C during the day, and 17–24°C at night. In 1974–1993, a total of 91 eggs from five wetlands were transferred to the laboratory. In 1974–2012, a total of 258 eggs from 11 wetlands were monitored in 27 caged and 55 uncaged nests. Cages were 1 cm wire mesh and buried 8–15 cm into the ground. All eggs were monitored for at least 8–9 weeks to assess hatching success, and hatchlings from the laboratory were released at the original nest site within 5–10 days.Study and other actions tested
A study in 2015 in desert scrubland in California, USA (Daly et al. 2018) found that just over half of artificially incubated desert tortoise Gopherus agassizii eggs collected from wild adult females hatched in captivity. In total, 74 of 123 desert tortoise eggs hatched after being incubated in captivity (60% emergence success). Eggs were collected from 25 wild adult female desert tortoises in May-June 2015. Eggs were incubated in artificial burrows in an outdoor predator-proof nesting enclosure (in individual 5 x 9 m pens inside a 30 x 30 m enclosure).Study and other actions tested