Create artificial nests or nesting sites

Supporting evidence from individual studies

1. A replicated, before-and-after study in 1965–1971 in a captive breeding facility in the Galápagos, Ecuador (MacFarland et al. 1974) found that Galápagos giant tortoise Geochelone elephantopus hoodensis females successfully laid eggs when artificial nesting sites mimicking natural conditions were provided. Results were not statistically compared. During the first two nesting seasons, when no artificial nests were provided, females attempted to nest on successive evenings (approximately 20–30 nights attempted nesting/clutch) but eventually dropped eggs on the rocky surface (four clutches). After artificial nests without ideal substrate were provided, females attempted to nest on successive evenings (10–30 nights/clutch) and some eggs were deposited in artificial nesting sites (artificial sites: 2 nests; on rocky substrate: 2 nests). After provision of ideal soil substrate, nesting attempts were shorter (1–4 nights/clutch, rarely up to 12) and all eggs were deposited in artificial (17 nests) or natural sites (2 nests). One male and 10 female Galápagos giant tortoises were brought into a captive breeding enclosure to mate and nest from the 1967/1968 nesting season. In 1969/1970, three artificial nesting sites were built (coarse soil, minimum 3 m² and 35–40 cm deep). These were removed in the 1970/1971 and 1971/1972 nesting seasons, and replaced with four artificial nest sites with fine soil identical to that found in the natural nesting area (all other dimensions the same).

   Study and other actions tested

   Referenced paper

   MacFarland C.G., Villa J. & Toro B. (1974) The Galápagos giant tortoises (Geochelone elephantopus) Part II: Conservation methods. Biological Conservation, 6, 198-212.

2. A study in 1993 on an island in the Columbretes archipelago, Spain (Castilla & Swallow 1995) found that all of 15 artificial nests were visited by Iberian wall lizards Podarcis hispanica atrata and one nest contained a clutch of laid eggs. All 15 artificial nests were used as basking and burrowing sites by adult male and female Iberian wall lizards (rocky area: total 3–17 active lizards/nest; vegetated area: 7–35 active lizards/nest). One artificial nest (in the vegetated area) had a clutch of two eggs laid in it, which hatched successfully. A total of 39 of 47 introduced eggs (83%) survived and developed successfully in the artificial nests. Fifteen white plastic containers (20 x 15 x 7 cm) filled with volcanic sand (five with rocks, five with stone shingle) were placed in a rocky area with a low density of lizards (seven containers; <100 lizards/ha) and a vegetated area with a high density of lizards (eight containers; 800 lizards/ha). Containers were covered with stone slabs and placed on the ground 5–15 m apart surrounded by rocks. Water was added every other day. In May–July 1993, lizards and their faecal pellets and burrows were counted during 40 x 5-minute observations over 19–20 days. All 15 containers were searched for naturally laid eggs on two occasions. Three introduced eggs (laid by captive female lizards) were placed in each container and survival recorded weekly.

   Study and other actions tested

   Referenced paper

   Castilla A.M. & Swallow J.G. (1995) Artificial egg-laying sites for lizards: a conservation strategy. Biological Conservation, 72, 387-391.

3. A study in 2009 in vegetated pond banks in Anhui, China (Wang et al. 2011) found that Chinese alligators Alligator sinensis nested at a quarter of sites where artificial nesting materials were provided. Chinese alligators constructed nests at 11 of 43 sites where artificial nesting materials were provided. In addition, Chinese alligators constructed nests at eight locations across the whole study area where nesting materials were not provided. In May 2009, artificial nesting materials were provided in 43 sites in an outdoor alligator captive-breeding enclosure. The enclosure was surrounded by a 2.1 m high fence and included eight natural ponds surrounded by native vegetation. In total, 211 adult Chinese alligators had been introduced to the enclosure (0.024 alligators/m²). The banks of all ponds (areas with and without provided nesting material) were monitored daily in the first part of July 2009 for signs of nesting activity.

   Study and other actions tested

   Referenced paper

   Wang J., Wu X.B., Tian D., Zhu J., Wang R. & Wang C. (2011) Nest-site use by the Chinese alligator (Alligator sinensis) in the Gaojingmiao breeding farm, Anhui, China. Asian Herpetological Research, 2, 36-40.

4. A study in 2009–2011 in tropical rainforest on Reunion Island, Indian Ocean (Sanchez 2012) found that some artificial egg-laying sites in a habitat restoration area were used by Reunion day geckos Phelsuma borbonica in the year they were installed and the number of sites used and eggs laid increased in the second year. Nine months after artificial egg-laying sites were installed, four of 34 sites were used by geckos and 10 eggs were laid. Two years after the first artificial egg-laying sites were installed, eight of 40 sites were used by geckos and 41 eggs were laid. In total, 40 artificial egg-laying sites were added to an area (9,000 m²) of degraded habitat in a hydroelectric power plant in September 2009–July 2010 (34 were installed by June 2010 and a further 6 by July 2010). Artificial egg-laying sites comprised hollow, rectangular metal poles (4 x 8 x 250 cm) inserted into the ground (50 cm deep). Native plant species were planted in the same area to restore habitat (22,000 plants of 50 species). Egg-laying sites were monitored for signs of geckos and egg laying in June and September 2010, and March and September 2011.

   Study and other actions tested

   Referenced paper

   Sanchez M. (2012) Mitigating habitat loss by artificial egg laying sites for Reunion day gecko Phelsuma borbonica, Sainte Rose, Reunion Island. Conservation Evidence, 9, 17-22.

5. A replicated, controlled study in 2009–2010 in a mosaic of wetlands, rivers and lakes in Ontario, Canada (Paterson et al. 2013) found that freshwater turtle species used artificial nest mounds more than expected, and eggs in artificial mounds had higher hatching success than eggs left in natural nests. Turtles used artificial nests more than expected by chance (artificial mounds constituted 2% of nesting habitat but hosted 4% of nests). Of the four turtles that used the artificial mounds (1 painted turtle Chrysemys picta, 1 snapping turtle Chelydra serpentina, 2 Blanding's turtle Emydoidea blandingii), all had 100% hatching success. Eggs transplanted to artificial nests had higher hatching success than those left in natural nests for nine painted turtle nests (artificial: 98%; natural 71%) and 12 snapping turtle nests (artificial: 88%; natural 56%). Four artificial nesting mounds (60% gravel and 40% sand) 6 m diameter and 0.5 high were installed in April 2009 on top of a layer of geotextile cloth. Each mound was within 100 m of water, 50 m of a known nesting site and sited to prevent nesting turtles from having to cross a road. All natural, artificial and potential nesting mounds within 1 km of each artificial mound were monitored nightly from May-June 2009–2010. For the transplant experiment, nests were excavated and split evenly between the closest artificial mound and the original nest. Hatching events were monitored from August, and nests were excavated in October to assess hatching success.

   Study and other actions tested

   Referenced paper

   Paterson J.E., Steinberg B.D. & Litzgus J.D. (2013) Not just any old pile of dirt: Evaluating the use of artificial nesting mounds as conservation tools for freshwater turtles. Oryx, 47, 607-615.

6. A replicated, controlled study in 2006–2007 on an island of salt marsh grasses in New Jersey, USA (Wnek et al. 2013) found that hatching success of diamondback terrapin Malaclemys terrapin nests in artificial nesting mounds varied depending on the construction material and year when compared to natural nests.  Dredge soil mounds produced no hatchlings in the first year (0 of 10 nests hatched) but had some success in the second year (10 of 12 nests hatched, 42–60% hatching success). Loamy-sand mounds produced hatchlings in both years (11–85% hatching success). Hatching success in sand mounds varied from 0–31% in the first year and 41–65% in the second year. Natural nests had hatching success of 54% in the first year and 70% in the second year. Three experimental plots (2.25 m²) were filled with 45cm of soil:  dredge soil from a nearby channel which had been dried for two months; loamy sand from a natural nesting area or sand from a beach. One half of each plot was shaded by shade cloth 15 cm above the soil with the other half in full sun and each nest had a predator excluder made of wire mesh. Natural nests were in full sun with nearby vegetation cover. Clutches were relocated to treatment plots from areas with high human activity (2006: 5 nests/treatment, 5 natural controls; 2007: 6 nests/treatment, 8 natural controls). Nests were excavated after 60 days to assess hatching success.

   Study and other actions tested

   Referenced paper

   Wnek J.P., Bien W.F. & Avery H.W. (2013) Artificial nesting habitats as a conservation strategy for turtle populations experiencing global change. Integrative Zoology, 8, 209-221.

7. A replicated study in 2013–2014 on an island site between a saltmarsh and road in Georgia, USA (Quinn et al. 2015) found that diamondback terrapins Malaclemys terrapin made use of artificial nest mounds, and an electrified nest box provided more protection from predation than a nest box alone. At least 37 nests were laid in nest mounds (number of confirmed nests from table), yielding at least 203 hatchlings. Fewer nests laid under a nest box with an electric wire were predated (1 of 27 nests found) compared to those under a nest box with no wire (16 of 16 nests found). An artificial nesting mound (22.9 m long × 3.6 m wide × 1.2 m tall) was constructed using dredge material along the shoulder of an 8.7 km causeway leading to the island. On top of the mound were placed six nest boxes (3.7 x 1.2 x 0.6 m) with a ground-level 9 cm horizontal gap to allow terrapins access but to exclude predators. For 35 days from May–June 2013, one nest box was modified to include a battery-powered electric wire along the horizontal gap opening and for 26 days from June–July 2013, all six nest boxes had electric wires. The mound was excavated to find nests and hatched eggs in November 2013 and April 2014.

   Study and other actions tested

   Referenced paper

   Quinn D.P., Kaylor S.M., Norton T.M. & Buhlmann K.A. (2015) Nesting mounds with protective boxes and an electric wire as tools to mitigate diamond-backed terrapin (Malaclemys terrapin) nest predation. Herpetological Conservation and Biology, 10, 969-977.

8. A study in 2000–2008 on a roadside verge along a river bank in Pennsylvania, USA (Nagle & Congdon 2016) found that sand and shale mounds built along a barrier fence as mitigation nesting habitat after a road was constructed were used by a small number of nesting female northern map turtles Graptemys geographica in the first year. In the first year following creation of sandy mounds as nesting sites, two of 50 nests were laid in the sand mounds. The authors reported that most females walked over the sand mounds and nested near the barrier fence. In 1999, a new highway was built along a major river and in 2000 a chain-link fence (1 m high, 1,150 m long) was erected to mitigate road deaths of female turtles crossing the road to find suitable nesting habitat. Eight mounds of sand (800 m³ total volume) were created on the river side of the road fence to provide nesting habitat. In 2001, the sand was moved closer to the fence and shale was added to reduce vegetation. Turtle nesting was monitored in May–July 2000–2003, 2005–2007 and 2008 (dates not provided for 2008) in the mitigation nesting habitat and at another commonly used nesting site, but data on use of mitigation nesting sites were only provided for 2000.

   Study and other actions tested

   Referenced paper

   Nagle R.D. & Congdon J.D. (2016) Reproductive ecology of Graptemys geographica of the Juniata River in central Pennsylvania, with recommendations for conservation. Herpetological Conservation and Biology, 11, 232-243.

9. A before-and-after study in 1991–2015 in old-growth dry limestone forest in Jamaica (Wilson et al. 2016) found that when an artificial nesting site was created as part of a Jamaican iguana Cyclura collei head-starting programme, numbers of nesting female and hatchling iguanas increased over 23 years. Results were not statistically tested. Twenty-three years after the start of a Jamaican iguana head-starting programme involving building an artificial nesting site, 321 iguana hatchlings and 63 nesting female iguanas were counted compared to 31 hatchlings and nine nesting females at the start of the programme. Two nests were laid in the artificial nest site three years after it was built. In 1991–2015, Jamaican iguana eggs/hatchlings were collected for head-starting in a zoo and head-starters were released from 1996 (278 total head-starters released, usually 6–8 years old or 1–2 kg). In 1997–2014, non-native mammalian predators (mongoose Herpestes javanicus, cats Felis catus, dogs Canis lupus familiaris and feral pigs Sus sp.) were removed using baited cage traps, snares and leg-hold traps (~1,500 individual removed in ~350,000 trap days over 17 years using 20–300 cage traps). In 2011–2012, an artificial nesting site was constructed 40 m south of the main nesting area. During the nesting season in 1991–2015, nests were checked daily and adult female iguanas were monitored by live trapping, observation and camera traps.

   Study and other actions tested

   Referenced paper

   Wilson B., Grant T.D., Van Veen R., Hudson R., Fleuchaus D., Robinson O. & Stephenson K. (2016) The Jamaican iguana (Cyclura collei): a report on 25 years of conservation effort. Herpetological Conservation and Biology, 11, 237-254.