Remove or control predators using lethal controls: Tuatara

Overall effectiveness category Awaiting assessment
Number of studies: 1
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Effectiveness

not assessed
Certainty

not assessed
Harms

not assessed

Calculating overall effectiveness category

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. Removing or controlling predators, especially native predators, for the benefit of their wild prey species can be a controversial management strategy. Nonetheless, there is potential for such management to lead to increases in the abundance, survival or reproductive success for species of conservation concern.

Due to the number of studies found, this action has been split by species group, though no studies were found for amphisbaenians.

Study locations

Key messages

One study evaluated the effects of removing or controlling predators using lethal controls on tuatara populations. This study was in New Zealand.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Abundance (1 study): One replicated, controlled, before-and-after study in New Zealand found that after eradicating Pacific rats the abundance of tuatara was higher on islands where rats were eradicated than on islands where some rats remained, and that the percentage of total tuatara that were juveniles increased.

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 replicated, controlled, before-and-after study in 1979–2005 on four coastal forest-covered pacific islands, New Zealand (Towns et al. 2007) found that eradicating Pacific rats Rattus exultans using rodenticides increased the population density of tuatara Sphenodon punctatus and increased the proportion of juveniles. On the three rat free islands, 162 tuatara were found over a total area of 5 ha (1–2 ha/island), compared to 44 tuatara found on the island with rats over a 39 ha area (no statistical tests were carried out). The percentage of juvenile tuatara increased after rats were eradicated on three islands (5–43%) compared to before they were eradicated (0–9%), whereas the proportion of juveniles remained at 0% on an island without rat eradication over 21 years of monitoring. Smaller tuatara were observed more frequently and in a greater range of size classes after rat eradication (see original paper for details). Rats were managed on Whatupuke Island (eradicated: 1993; 102 ha), Lady Alice Island (eradicated: 1994; 155 ha), and Coppermine Island (heavily controlled: 1992–1993; eradicated: 1997; 80 ha) using rodenticide (brodifacoum, aerial deployments except Coppermine Island in 1992–1993 when rodenticide blocks were placed on the ground). Rats were not eradicated from Taranga Island (500 ha). Tuatara were monitored on all islands at night using spotlight searches before and after rat eradication (4.5–8.5 years after) and on Taranga island in 1984, 2000, and 2005.
Study and other actions tested
Referenced paper
Towns D.R., Parrish G.R., Tyrrell C.L., Ussher G.T., Cree A., Newman D.G., Whitaker A.H. & Westbrooke I. (2007) Responses of tuatara Sphenodon punctatus to removal of introduced Pacific rats from islands. Conservation Biology, 21, 1021-1031.

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?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Reptile Conservation

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