Action

Relocate nests/eggs for artificial incubation: Crocodilians

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

Study locations

Key messages

  • Six studies evaluated the effects of relocating nests/eggs for artificial incubation on crocodilian populations. Two studies were in the USA and one study was in each of Zimbabwe, Argentina, Venezuela and Australia.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (6 STUDIES)

  • Reproductive success (5 studies): Two replicated studies in Zimbabwe and the USA reported that hatching success for 20,000 Nile crocodile eggs and >30,000 American alligator eggs that were artificially incubated was 74% and 61%. Two studies (including one replicated study) in Argentina and Venezuela reported that 43–100% of road-snouted caiman eggs, 66% of American crocodile eggs and 54% of Orinoco crocodile eggs hatched successfully following artificial incubation. One replicated, before-and-after study in Australia reported that hatching success of artificially incubated saltwater crocodile eggs differed when the project was under local compared to external management.
  • Condition (1 study): One replicated, controlled, paired study in the USA found that American alligator eggs relocated for artificial incubation produced larger hatchlings than eggs left in situ.

BEHAVIOUR (0 STUDIES)

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 1967–1974 in three rearing stations along the Zambezi River in Zimbabwe (Blake & Loveridge 1975) found that three-quarters of artificially incubated Nile crocodile Crocodylus niloticus eggs hatched in captivity. Over seven years, artificially incubated Nile crocodile egg hatching success was 74% (16,697 of 22,697 eggs hatched). The authors reported that collecting eggs very soon after laying had a detrimental effect on hatching success. Nile crocodile eggs were collected from the wild, hatched and reared in three rearing stations (at Kariba Lake, Binga and Victoria Falls) as part of a crocodile farming initiative in 1967–1973 (128–2,475 eggs collected/station/year). Eggs were artificially incubated in captivity (no details are provided).

    Study and other actions tested
  2. A replicated study in 2001–2002 in a laboratory in Santa Fe province, Argentina (Larriera et al. 2006) found that artificially incubated broad-snouted caiman Caiman latirostris eggs hatched in captivity. Hatching success of artificially incubated broad-snouted caiman eggs taken from the wild ranged from 43–100% (hatching success of seven caiman nests: 30 of 36 eggs hatched; 18 of 37 eggs hatched; 35 of 41 eggs hatched; 20 of 30 eggs hatched; 13 of 30 eggs hatched; 18 of 26 eggs hatched; 35 of 35 eggs hatched). Between 1990 and 2002, a head-starting programme collected caiman eggs from wild nests (December–January), artificially incubated the eggs and reared hatchlings for up to nine months before releasing caiman (with individual scale markings) back into the collection site (see original paper for details). In austral summer 2001–2002, clutches from seven head-started female broad-snouted caiman were collected from the wild (26–41 eggs/nest) and artificially incubated (at 31.5°C and 95% relative humidity) until hatching.

    Study and other actions tested
  3. A replicated, controlled, paired study in 1999–2004 in an area of marsh in Louisiana, USA (Elsey & Trosclair 2008) found that relocating American alligator Alligator mississippiensis eggs for artificial incubation soon after laying resulted in heavier, longer hatchlings compared to eggs left in the nests until just before hatching. Eggs relocated soon after laying produced heavier (after hatching: 39–56 g; 6–9 months old: 795–1,270 g) and longer (after hatching: 24–26 cm; 6–9 months old: 63–78 cm) hatchlings than eggs from naturally incubated nests (mass: after hatching: 37–53 g; 6–9 months old: 795–1,130 g; length: after hatching: 23–26 cm; 6–9 months old:  62–74 cm). Alligator nests were located by helicopter and ground surveys (three nests in 1999 and six nests in 2003). Half of each clutch was relocated for artificial incubation soon after laying, whereas the other half was left in the nest and collected just prior to hatching. Relocated eggs were artificially incubated at 31–32°C. Weight and length of all hatchlings was measured two days after hatching, and then three more times at 2–3 month intervals.

    Study and other actions tested
  4. A study in 2009 in two river basins in Venezuela (Barros et al. 2010) found that most American crocodile Crocodylus acutus and Orinoco crocodile Crocodylus intermedius eggs hatched successfully after being collected from the wild and artificially incubated. Results were not statistically tested. In total 66% of American crocodile eggs (200 of 305 eggs) and 54% of Orinoco crocodile eggs (116 of 216 eggs) hatched successfully after artificial incubation. Egg collection was carried out in 2009 (521 eggs collected overall) in the Santa Ana (305 American crocodile eggs) and Manapire (216 Orinoco crocodile eggs) river basins. Eggs were transported to a brick-walled building in each location (25 m2 and 5 m2 in size) with a zinc roof closed to predator access. The larger incubation room temperature was maintained at 32ᵒC by five light bulbs. Eggs were stored in sand-filled insulated polystyrene boxes. The sand was kept damp by adding water at regular intervals.

    Study and other actions tested
  5. A replicated study in 2007–2012 in hatching facilities across six counties in Texas, USA (Eversole et al. 2013) found that artificially incubating American alligator Alligator mississippiensis eggs resulted in more than half of eggs hatching successfully. Average hatching success was 61% (average of 23 of 37 eggs/nest) and hatching success of viable eggs was 71% (average of 23 of 32 viable eggs/nest). In 2007–2012, a total of 33,454 eggs were collected from 902 wild alligator nests, and the viability of eggs was determined by examining egg colour, odour and presence of an opaque band. Eggs and nesting materials were transported in wire baskets to hatching facilities, where they were incubated at 31–32.8°C and 100% humidity, buried inside the nesting material. Eggs were removed from 50% of nests that were discovered during surveys, and surveys were carried out on foot, by boat and by helicopter.

    Study and other actions tested
  6. A replicated, before-and-after study in 1989–2015 in hatching facilities within four river systems in Northern Territory, Australia (Corey et al. 2018) found that artificially incubated saltwater crocodile Crocodylus porosus eggs hatched in captivity, but hatching success rates differed between local and external management. Results were not statistically tested. Hatching success of saltwater crocodile eggs as part of a sustainable harvest programme was 49% when run by a local Indigenous community organisation (654 hatchlings from 1,396 live eggs/year) compared to 84% when it was run by an external management company (1,413 hatchlings from 1,659 live eggs/year). Saltwater crocodile eggs were collected and incubated as part of a regional government-led sustainable harvest initiative. In 1989–1997 an external management company ran the programme. In 1998–2015 it was run by a local Indigenous management company. In 1996–1997 eggs were harvested by the external company and incubated by the Indigenous management company. There was no harvest in 2007–2008. Annual quotas were 2,700–3,000 eggs/year (total limit of 70,000 eggs/year across the territory). Eggs were incubated at a constant temperature of 32°C and ≥99% humidity. Local workers were paid based on the number of eggs collected and hatchlings produced.

    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.

Where has this evidence come from?

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Reptile Conservation

This Action forms part of the Action Synopsis:

Reptile Conservation
Reptile Conservation

Reptile Conservation - Published 2021

Reptile synopsis

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