Remove or control predators by relocating them

Overall effectiveness category Awaiting assessment
Number of studies: 2
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Background information and definitions

Predators can drive declines or local extinctions of vulnerable reptile species. Non-native predators may be a particular problem for native reptiles that lack sufficient predator avoidance behaviours. Native predators can also threaten populations of reptiles that persist in low numbers. Predator control may attract opposition on animal welfare grounds, and therefore relocating predators may be a more favourable option in some circumstances.

Se also: Remove or control predators using fencing and/or aerial nets and Remove or control predators using lethal controls.

Study locations

Key messages

Two studies evaluated the effects on reptile populations of removing or controlling predators by relocating them. Both studies were in the USA.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (2 STUDIES)

Abundance (1 study): One before-and-after study in the USA found that after raccoons were live trapped and relocated, the number of freshwater turtle hatchlings increased for 2–3 years, then decreased again after 3–4 years.
Reproductive success (2 studies): One of two studies (including one replicated, controlled study) in the USA found that within a fenced area where predators were removed by both relocating and lethal controls, fewer gopher tortoise nests were predated than outside the fenced area where predators were not removed. The other study found that after raccoons were live trapped and relocated, predation of freshwater turtle nests decreased for 2–3 years, then increased again after 3–4 years.
Survival (1 study): One replicated, controlled study in the USA found that within a fenced area where predators were removed by both relocating and lethal controls, survival of gopher tortoise hatchlings was higher than outside the fenced area where predators were not removed.

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

A before-and-after study in 1978–1982 around ponds and sand dunes in Iowa, USA (Christiansen & Gallaway 1984) found that following removal of racoons Procyon lotor, the number of turtle hatchlings increased, and nest predation decreased for the first few years. Results were not tested statistically. Nest predation decreased for two years following racoon removal (before removal: 18 nests destroyed; after removal: 5 and 4 nests destroyed), but increased again 3–4 years after removal (21 and 28 nests destroyed). Abundance of hatchlings increased for three years (before removal: 15 hatchlings; after removal: 75, 80 and 74 hatchlings), but then decreased four years after removal (30 hatchlings). The most abundant turtle species was the yellow mud turtle Kinosternon flavescens (167 hatchlings seen in total). Raccoons were live trapped during 1979 and relocated to a site 24 km from the study site. Surveys for hatchlings and destroyed nests were conducted in 1978–1982. Turtle nesting areas were monitored twice/week and hatchling turtles were sampled using drift fences placed between ponds and known nesting areas 3–30 m from water and pitfalls.
Study and other actions tested
Referenced paper
Christiansen J.L. & Gallaway B.J. (1984) Raccoon Removal, Nesting Success, and Hatchling Emergence in Iowa Turtles with Special Reference to Kinosternon flavescens (Kinosternidae). The Southwestern Naturalist, 29, 343-348.
A replicated, controlled study in 2002–2005 in a pine forest in Georgia, USA (Smith et al. 2013) found that removal of predators using relocations and lethal controls from fenced exclosures resulted in higher survival of gopher tortoise Gopherus polyphemus nests and hatchlings compared to areas with no fencing or predator removal. The effects of predator removal (both relocations and lethal controls) and fencing cannot be separated. Survival was higher inside fenced areas with predator removal compared to outside for both nests (Fenced: 52 of 78, 66% survived; Un-fenced: 26 of 73, 35%) and hatchlings (Fenced: 74% survived for 1 year; Un-fenced: 38%). In 2002–2003, four plots (40 ha) were randomly selected and enclosed in 1 m high mesh fence with electrical wires at the top and bottom. A further four plots were left un-fenced. In 2002–2003, all mammalian predators within the exclosures were live-trapped and removed, and in 2003–2005, further trapping of meso-predators was conducted. Predators that re-entered exclosures were euthanized. In May–June 2003–2005, all tortoise burrows were searched for nests, and all active nests were monitored 1–2 times/week up to 110 days. In 2004, forty hatchlings from 13 different nests were fitted with radio transmitters and monitored for up to a year.
Study and other actions tested
Referenced paper
Smith L.L., Steen D.A., Conner L.M. & Rutledge J.C. (2013) Effects of predator exclusion on nest and hatchling survival in the gopher tortoise. Journal of Wildlife Management, 77, 352-358.

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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This Action forms part of the Action Synopsis:

Reptile Conservation

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