Action

Translocate adult or juvenile reptiles: Snakes

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

Study locations

Key messages

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (12 STUDIES)

  • Abundance (6 studies): One of two global reviews reported that 15 of 47 reptile translocations (number of snake species not provided) resulted in stable or growing populations (both wild-caught and captive bred reptiles or snakes). The other review reported that the outcome of one indigo snake reintroduction was unknown. One replicated study in the USA found that five of 13 translocations of snakes resulted in established populations. Three studies in Canada and Antigua reported that 3–7 years after translocations of red-sided garter snakes and Antiguan racer snakes, greater numbers were counted.
  • Reproductive success (3 studies): One global review reported that breeding occurred in nine of 22 reptile translocations (of both wild-caught and captive bred animals). Two studies in Antigua reported successful reproduction in translocated populations of Antiguan racer snakes three years after release.
  • Survival (8 studies): Three controlled studies in the USA and Australia found that translocated timber rattlesnakes, northern water snakes and dugite snakes had lower survival than resident snakes, and in one study no translocated snakes survived a year. One controlled study in the USA found that ratsnakes held in captivity for 1–7 years before release had lower survival compared to snakes held for 7–18 days or resident snakes. Four studies (including one replicated, controlled study) in Canada, the USA and South Korea reported that 12–45% of snakes survived for three months to eight years after release.
  • Condition (1 study): One controlled study in the USA found that translocated northern water snakes had similar growth rates compared to resident snakes.

BEHAVIOUR (5 STUDIES)

  • Behaviour change (5 studies): Three of five controlled studies in the USA found that differences in movement and home range size of translocated and resident hognose snakes, ratsnakes and dugite snakes were mixed. The other two studies found that translocated timber rattlesnakes and northern water snakes had larger home ranges than residents. One study also found that translocated timber rattlesnakes had higher daily movements than resident snakes.

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 review of worldwide translocation programmes for reptiles during 1962–1990 (Dodd & Seigel 1991) reported that the outcome of one programme involving indigo snakes Drymarchon corais was unknown. The origin of individuals (wild populations or captive-bred) was not described for this programme. Published and unpublished literature was searched.

    Study and other actions tested
  2. A study in 1985–1988 at a hibernaculum in a limestone sinkhole in Manitoba, Canada (Macmillan 1995) found that around 12% of translocated red-sided garter snakes Thamnophis sirtalis parietalis were recaptured after one winter and none were recaptured at the donor site. After one winter, 84 of 720 translocated snakes (12%) were recaptured at the hibernaculum. One translocated snake was recaptured during the following autumn and spring, but sampling was disrupted by commercial snake harvesters. None of the 720 translocated snakes were recaptured at the donor site. The authors reported that three years after the translocation the population consisted of around 800 snakes, 427 if which were new captures. The hibernaculum had been uninhabited since heavy flooding in 1974. In September–October 1985, a total of 720 snakes (451 males, 269 females) were collected at a hibernation site and released at an empty hibernaculum 55 km away. All translocated snakes were individually marked by ventral scale clipping. Snakes were collected periodically at both sites in spring and autumn 1986, spring 1987 and spring 1988 (sampling methods not reported).

    Study and other actions tested
  3. A controlled study in 1990–1994 in a site of mixed broadleaf forest in Pennsylvania, USA (Reinert & Rupert 1999) found that translocated timber rattlesnakes Crotalus horridus had higher mortality and moved longer distances than resident rattlesnakes. Translocated rattlesnakes had higher mortality (55% died; 6 of 11 rattlesnakes) than resident rattlesnakes (11%; 2 of 18 rattlesnakes). Translocated snakes had higher daily movements (average daily movement: 55–124 m) compared to resident rattlesnakes (10–37 m), moved more overall in two of three comparisons and had larger ranges in nine of 12 comparisons (see paper for details). In 1991–1992, eleven rattlesnakes (five females, six males) were equipped with radio transmitters and translocated between eight and 172 km from point of capture. In 1990–1992, eighteen resident rattlesnakes (10 females, eight males) were also monitored using radio telemetry. Rattlesnakes were located once every two days for six months of the year (mid-April to mid-October) for up to a year.

    Study and other actions tested
  4. A controlled study in 1992–1994 in a site of deciduous forest in Arkansas, USA (Plummer & Mills 2000) found that translocating eastern hognose snakes Heterodon platirhinos resulted in only one surviving until hibernation. Similar numbers of translocated snakes were predated (5–6 of 8) compared to resident snakes (6 of 8). Translocated snakes survived 3–75 days, whereas residents survived 24–183 days (values taken from table). Average movement of translocated snakes (120 m/day) was similar to residents (119 m/day), but variability in daily movement was nearly six times higher for translocated snakes than residents. Translocated snakes were captured offsite from various localities 8–40 km from the translocation site and resident snakes were captured on site. Snakes were implanted with radio transmitters and released within 5 days of capture in a grassy clearing.  Snakes were located daily from April to October 1992–1994.

    Study and other actions tested
  5. A replicated study in 1980–1999 in five upland sites near to New York, USA (Cook 2002) found that of 13 translocations of snakes, at least five resulted in established populations. Five of 13 translocations of three species (northern brown snake Storeria dekayi, eastern milk snake Lampropeltis triangulum triangulum, black racer Coluber constrictor) resulted in established populations; four translocations of four species were likely to have been successful based on persistence of offspring records (smooth green snake Opheodrys vernalis, eastern hognose snake Heterodon platirhinos, eastern milk snake, black racer) and one translocation of eastern hognose snakes failed. The success of three translocations could not be assessed because of insufficient data (smooth green snake, eastern hognose snake, northern water snake Nerodia sipedon). In 1980–1995, six species of locally caught snakes of different life stages were translocated to one or more of five sites. At one of the sites, coarse woody debris and some temporary and permanent freshwater ponds were also added. Monitoring involved funnel traps, drift-fences with pitfall traps, artificial coverboards, visual searches and radio-telemetry.

    Study and other actions tested
  6. A study in 1980–2001 on an island off the coast of Florida, USA (Irwin et al. 2003) found that a small number of released eastern indigo snakes Drymarchon couperi survived 5–8 years in the wild. In the 17–20 years after 40 eastern indigo snakes were released, five snakes were recorded in the wild and the last snake was observed 5–8 years after release (1983: 1 individual; 1985: 1 individual; 1986: 2 individuals; 1988: 1 individual). In 1980–1982, forty eastern indigo snakes (hatchlings and juveniles from a captive breeding colony, wild-caught adults, confiscated snakes and donated from zoos) were released onto St Vincent Island National Wildlife Refuge (51 km2). Snakes were monitored using combinations of cameras in gopher tortoise Gopherus polyphemus burrows and drift fence/pitfall trap arrays in autumn, winter and spring 1983–1990, January and December 2000, and April 2001. Sightings (unverified) were also recorded but are not reported here.

    Study and other actions tested
  7. A study in 1999–2006 on a coastal forest offshore island in Antigua (Daltry 2006) found that a population of Antiguan racer snakes Alsophis antiguae translocated to a rat-free island survived at least seven years and bred in the wild. After three years, the first adult offspring was recorded (one individual). After four years, 15 new snakes were recorded. After seven years, the total population was estimated to be 40–50 adult and subadult snakes. Monitoring of the translocated snakes after release indicated that they were hunting and feeding successfully. In total 10 wild-caught snakes were introduced to Rabbit Island (2 ha) in November-December 1999. Five snakes were implanted with radio transmitters for monitoring up to 6 months after their release. All snakes are marked with PIT tags. Black rats Rattus rattus were eradicated from the island in 1998.

    Study and other actions tested
  8. A study in 2002–2006 on a coastal forest island in Antigua (Daltry 2006) found that a population of Antiguan racer snakes Alsophis antiguae translocated to a predator-free island survived at least three years and bred successfully in the wild. Young racer snakes were observed three years after snakes were first translocated and the population had approximately doubled to 98 snakes three years after the first release (data presented in 7). Monitoring of adult female snakes found that two of them had increased in weight and length in the year after being released. In total 45 wild-caught snakes were transported to and released onto Green Island (43 ha) in 2002–2005. Four female snakes were implanted with radio transmitters for post release monitoring in 2003. Black rats Rattus rattus were eradicated from the island in 2002 but returned in 2006.

    Study and other actions tested
  9. A review of worldwide reptile translocation projects during 1991–2006 (Germano & Bishop 2009) found that a third were considered successful with substantial recruitment to the adult population. Of the 47 translocation projects reviewed (39 reptile species), 32% were successful, 28% failed and long-term success was uncertain for the remaining 40%. Projects that translocated animals due to human-wildlife conflicts failed more often (63% of 8 projects) than those for conservation purposes (15% of 38) and those for research purposes (50% of 5). Success was independent of the source of animals (wild, captive, and combination), life-stage translocated, number of animals released and geographic region (see original paper for details). Translocated animals were adults in 75% of cases, juveniles and sub-adults in 64% of cases and eggs in 4% of cases. Wild animals were translocated in 93% of projects. The most common reported cause of failure was homing and migration with the second most common reported cause being insufficient numbers, human collection and food/nutrient limitation all equally reported. Success was defined as evidence of substantial recruitment to the adult population during monitoring over a period at least as long as it takes the species to reach maturity. 

    Study and other actions tested
  10. A controlled study in 2008–2009 in a site of mixed hardwood forest and scrub patches in Indiana, USA (10) found that translocated northern water snakes Nerodia sipedon sipedon had lower survival compared to resident snakes, as well as larger home ranges but similar growth rate. Three of 10 translocated snakes survived five months (annual survival estimated at 20 %) to hibernation but none survived one year compared to seven of 12 resident snakes surviving to hibernation (58% survival) and four surviving to the end of the year (annual survival estimated at 45 %). Translocated snakes had larger home ranges (translocated: 14 ha; resident: 5 ha) but similar growth compared to resident snakes (translocated: 0.07 cm/day & 1.25 g/day; resident: 0.07 cm/day & 0.80 g/day). Translocated snakes were also more likely to leave the release area (40% of snakes) than residents (0%). In May 2008, ten snakes were captured from a site 5 km from the release site, along with 12 resident snakes. All were implanted with radio transmitters (7–11 days in captivity for recovery) before being released. Snakes were located once/week during the active season and once/two weeks when entering and leaving hibernation.

    Study and other actions tested
  11. A replicated, controlled study in 2008–2009 in two areas of montane mixed oak forest in central South Korea (Lee & Park 2011) found that some translocated Amur ratsnakes Elaphe schrenckii survived 10 months after release. Five of 11 translocated ratsnakes and two of two resident ratsnakes were alive 10 months after release. Within 10 days of release, three translocated snakes died (two were killed by predators) and two translocated snakes lost transmitter signal. One further translocated snake was lost later in the study. In July 2008, thirteen ratsnakes were surgically implanted with radio-transmitters and released into two valleys in a national park (288 km2). Two ratsnakes were locally-captured resident females that were released back to their original location (one/valley). Eleven ratsnakes had been illegally collected at least 9 km away from the release sites in April–July 2008 and, after being requisitioned by the police and park rangers, were kept in captivity prior to being translocated (five were released in one valley, six in another). All snakes were radio-tracked July 2008–May 2009: weekly in July–December 2008 and April–May 2009, and monthly in January–March 2009. All translocated snakes that were still being tracked at the end of the study were recaptured and put into a captive breeding programme.

    Study and other actions tested
  12. A controlled study in 2012–2015 in a mixed forest and wetland in South Carolina, USA (DeGregorio et al. 2017) found that that translocated ratsnakes Pantherophis obsoletus that spent longer in captivity had lower survival rates. The longer wild-caught translocated snakes spent in captivity prior to release, the lower their seasonal survival rates were compared to translocated snakes that spent less or no time in captivity (results reported as model outputs). Overall, 11 of 19 wild-caught snakes kept in captivity died after release compared to none of five released directly into the wild and three of 11 wild resident snakes (result was not statistically tested). Snakes that spent more time in captivity were more likely to be found in exposed locations than resident or direct-to-wild translocated snakes (see paper for details). Wild-caught snakes (19 individuals) were kept in captivity for between 13 months and 7 years before being fitted with radio transmitters and released in May 2014. An additional 11 resident snakes and five snakes to be translocated directly from the wild were caught, fitted with transmitters and released into the study site 7–18 days after capture. Snakes were radio tracked five-times/week in May–September 2014, once a week in September–December 2014 and once–twice in spring 2015.

    Study and other actions tested
  13. A controlled study in 2012–2015 in a mixed forest and wetland in South Carolina, USA (DeGregorio et al. 2017) found that translocated ratsnakes Pantherophis obsoletus that spent time in captivity before release had similar home ranges to resident snakes regardless of whether their environment was enriched prior to release, whereas translocated snakes kept in captivity without enrichment moved less each day than snakes translocated directly to the wild. Enriched- and unenriched-captive held snakes had similar home range sizes (enriched: 39 ha; unenriched: 23 ha) to resident snakes (26 ha), whereas snakes translocated directly to the wild had larger home ranges (93 ha). Enriched-captive snakes moved similar average daily distances to resident and direct translocated snakes in June–October, but unenriched-captive snakes moved less than directly translocated snakes in July, August and October (see original paper for details). Wild-caught snakes were kept either in unenriched (10 individuals, individually housed with bedding, food and water) or enriched conditions (9 individuals, additionally provided materials to encourage climbing, foraging and thermoregulatory behaviours) for 13 months to 7 years prior to release. Snakes were fitted with radio transmitters and released in May 2014. In addition, 11 resident snakes and five wild translocated snakes were caught, fitted with transmitters and released into the study site 7–18 days after capture. Snakes were radio tracked > once/week in May–September 2014, once/week in September–December 2014 and once or twice in spring 2015.

    Study and other actions tested
  14. A controlled study in 2015–2017 in a suburban area in Perth, Australia (Wolfe et al. 2018) found that translocated dugite snakes Pseudonaja affinis (urban or problem individuals) had higher mortality rates and larger activity range than resident snakes. Translocated snakes had larger maximum activity ranges (11 m2/day) compared to resident snakes (1 m2/day). Translocated snakes travelled similar distances (31 m/day) to resident snakes (11 m/day). All translocated snakes died during the study (4 of 4 individuals) compared to half of the resident snakes (3 of 6 individuals). Deaths were caused by predation or road collisions. In total 10 snakes (four translocated snakes and six resident snakes) were tracked for up to 2 months each in September-December 2015–2017. Snakes were either caught opportunistically in urban areas (two individuals) or reported as problem individuals (eight individuals).

    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

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