Remove or control invasive or problematic herbivores and seed eaters

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

Study locations

Key messages

  • Seven studies evaluated the effects of removing or controlling invasive or problematic herbivores and seed eaters on reptile populations. Three studies were in Australia and one study was in each of Mauritius, New Zealand, the USA and the Galápagos.


  • Richness/diversity (2 studies): One of two studies (one site comparison study and one controlled study) in the USA and Australia found that areas where feral horses had been removed had higher lizard and snake species richness than sites with horses. The other study found mixed effects of fencing in combination with removal of invasive mammals on reptile species richness.


  • Abundance (7 studies): Four of seven studies (including four controlled studies) in Mauritius, New Zealand, the USA, Australia and the Galápagos found that controlling European rabbits, grey kangaroos or herbivores and predators, in some cases using fencing, had mixed effects on the number of sightings or abundance of different reptile species. Two studies found that when both rabbits and Pacific rats or feral goats were removed the abundance of lizards or the percentage of giant tortoises that were juveniles. The other study found that areas where feral horses had been removed had similar lizard and snake abundance compared to sites with horses.


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 before-and-after study in 1982 and 1989 on a volcanic island in Mauritius (North et al. 1994) found that European rabbit Oryctolagus cuniculus eradication resulted in increased encounter rates of four of six reptile species. Results were not tested statistically. Daytime encounter rates increased after rabbit eradication for four species (by 0.2–2.3 individuals/hour), decreased for one species (by 2.1 individuals/hour) and stayed the same for one species (0.5 individuals/hour both years). Night-time encounter rates increased for five species (by 0.2–1.7 individuals/hour) and stayed the same for one species (0 individuals/hour in both years). For six reptile species, the total number of individuals encountered was higher following rabbit removal (37–1,363 individuals/species seen) compared to before rabbit removal (8–883 individuals/species seen), though survey effort was higher in 1989 than in 1982. In 1986, rabbits were eradicated from the island over a period of 2 months using (an unspecified) poison. Goats had been removed by progressive shooting in 1978. Three areas on the island were searched for reptiles by teams of up to seven people that thoroughly searched all vegetation. In 1982, survey effort was 59 person hours/day and 25 person hours/night, and in 1989, effort was 117 person hours/day and 49 person hours/night.

    Study and other actions tested
  2. A before-and-after study in 1986–1992 on two islands near North Island, New Zealand (Towns 1994) found that eradication of European rabbits Oryctolagus cuniculus and Pacific rats Rattus exulans resulted in an increase in the abundance of resident lizards. Results were not statistically tested, and effects of herbivore and predator control cannot be separated. In forest sites, lizard numbers remained stable for five years following eradication (1986–1991: 2 lizards/100 trap days) before increasing suddenly (1992–1993: 16 lizards/100 trap days). In coastal sites there was a gradual increase from the year of eradication (3 lizards/100 trap nights) to six years after eradication (70 lizards/100 trap nights). On a nearby predator free island, lizard abundance was 4 lizards/100 trap nights in forested areas and 15–60 lizards/100 trap nights in coastal areas. Rats and rabbits were eradicated in 1986–1987 from one island (rodenticide and shooting) and a nearby island was historically free of invasive mammals. In 1986–1993, lizards were counted using pitfall traps (initially 49, increased to 69 traps over 580 m2 on removal island) that were monitored twice/year (March and November).

    Study and other actions tested
  3. A site comparison study in 1998 in seven sites of sagebrush steppe in the Great Basin, USA (Beever & Brussard 2004) found that sites where feral horses Equus caballus had been removed had more lizard and snake species but similar abundances compared to grazed sites. Sites where horses had been removed had higher species richness (5 species/site) compared to sites with feral horses (2 species/site), but similar total abundance of individuals (horses removed: 11 individuals/site; horses present: 5 individuals/site). In addition, authors reported that the percentage of expected reptile species (% of those historically present) was similar for sites with and without horse removal. Ten horse-removed and nine horse-occupied plots (135 x 135 m) were chosen that had no recent fires (<15 years); were unused by cattle for at least 20 years; and were dominated by sagebrush (Artemisia tridentala). Only low elevation sites were included in analysis for reptiles (5 horse occupied plots; 6 horse removed plots across 7 sites). Horses were removed 10–14 years prior to the study. Sightings of reptiles within and adjacent to (≤20 m) a trapping grid (established for small mammal trapping) were recorded during May–August 1998.

    Study and other actions tested
  4. A controlled study in 1998–2005 in a site of dunes and shrubland in South Australia, Australia (Moseby et al. 2009) found that removing invasive European rabbits Oryctolagus cuninculus, cats Felis catus and foxes Vulpes vulpes within a fenced area, in combination with reintroducing native mammals, had mixed effects on reptile abundance and species richness 1–3 year and 4–8 years after fencing and removal began. Data reported on log scale or as statistical model results. During the first three years (1998–2000), reptile abundance and species richness were similar inside and outside the fenced area (native mammals reintroduced to fenced area in 1999). In the following five years (2001–2005), the abundance of reptiles was lower inside an expanded fenced area (one area with and one without native mammals) than outside, and richness was higher in one fenced area (no native mammals) than in both the other fenced area (with mammals) and outside the fence. A netting fence was constructed in 1997 and all rabbits, cats and foxes were removed. In 1999, locally extinct small mammals were reintroduced to the fenced area. The fenced area was expanded four times in 1999–2005, and one area received no native small mammals. In 1998, twenty-four trapping sites (12 inside the fence, 12 outside) were established. In 1999, six “outside” sites became “inside” sites as the fenced area expanded, and five new “outside” sites were established. Sites were trapped for four nights (6 pitfall traps, and 10 m drift fence) in April 1998–2000 and February 2001–2005.

    Study and other actions tested
  5. A paired sites, controlled, before-and-after study in 1993–1996 and 2007 in chenopod scrubland in South Australia, Australia (Read & Cunningham 2010) found that fencing to exclude herbivores and predators had mixed effects on different reptile species and species groups. One gecko species increased and two geckos decreased in abundance after exclusion fencing was added, compared to before when the same plots were grazed (knob-tailed gecko Nephrurus levis after fencing: 3.3 individuals/plot vs. grazed: 0.3–0.5 individuals/plot; tessellated gecko Diplodactylus tessellatus 0.0 vs. 1.3–1.8; variable fat-tailed gecko Diplodactylus conspicullatus 0.4 vs. 1.5–1.9). See paper for details of other species responses. Five grazed sites and four paired sites of differing grazing pressure were set out in 1993 (low intensity grazing: <12 cattle dung/ha; medium: 12–100; high: >120). Following the initial four years of the study, three of the eight grazing pressure sites were fenced to exclude cattle and predators. Reptiles were sampled for 10 days in summer from 1993–1996 and 2007 using 300 mm long flymesh drift fences with 13 unbaited pitfall traps (500 mm deep x 150 mm wide, 8 m apart). Lizards were marked by toe clips.

    Study and other actions tested
  6. A replicated, controlled study in 2007–2010 in two grassy woodland reserves near Canberra, Australia (Manning et al. 2013) found that fencing to reduce grey kangaroo Macropus giganteus grazing intensity had mixed effects on small skink abundance compared to not fencing depending on the amount of vegetation and whether coarse woody debris was added. At high vegetation density, small skink abundance increased over four years in fenced areas, but decreased in unfenced areas, whereas at medium-density vegetation the reverse was true (results reported on log scale). At low-density vegetation, small skink numbers remained stable over four years in both fenced and unfenced areas. In fenced low and medium-density vegetation sites, adding coarse woody debris (particularly 20 tonnes/ha clumped) lead to an increase in small skink abundance over time compared to when no debris was added (see paper for details). Reptiles were monitored in 96 plots (1 ha) in 24 sites across two nature reserves (4 plots/site). In October 2007, coarse woody debris was added to 72 plots (either 20 tonnes/ha evenly dispersed, 20 tonnes/ha clumped, 40 tonnes/ha dispersed and clumped) and none added to 24 plots. In December 2007, six sites were fenced to exclude kangaroos and grazing levels were classed as low (fenced: 0.4 kangaroos/ha) or high (unfenced: 2.1). Reptiles were surveyed at each site using 30-minute active searches from March to April in 2007–2010.

    Study and other actions tested
  7. A controlled study in 1995–2005 on two islands in the Galápagos (Márquez et al. 2013) found that removing feral goats Capra hircus resulted in an increase in the percentage of juvenile giant tortoises Chelonoidis nigra vandenburghi, whereas the percentage of juvenile giant tortoises on an island with no goat removal remained stable. With goat removal, the percentage of tortoises captured that were juveniles was higher in the second phase of goat removal (2000–2005: 24% of tortoises were juveniles) compared to the first phase (1995–1999: 5% juveniles), whereas at two locations with no goat removal juvenile numbers remained constant (1995–1999: 3% and 1%; 2000–2005: 1% and 2%). With goat removal, a total of 669 tagged tortoises were recaptured over the course of the study, and with no goat removal, 103 tortoises were recaptured. Goat removal was carried out on one island in 1995–2005. A total of 62,868 goats were removed, with around 85% of those goats being removed in the initial phase (1995–1999). No goat control was carried out on the other island. On the goat removal island, tortoises were sampled along 2–8 km long transects (placed randomly in four altitudinal zones) for 11 years; twice a year from 1995–2000 and once a year from 2001–2005, and all tortoises were individually marked. The same monitoring approach was used at two locations on the island without goat removal.

    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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Reptile Conservation

This Action forms part of the Action Synopsis:

Reptile Conservation
Reptile Conservation

Reptile Conservation - Published 2021

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