Remove or control predators using lethal controls: Tuatara

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

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.



  • 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.


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, 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
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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