Responses of tuatara Sphenodon punctatus to removal of introduced Pacific rats from islands

  • Published source details 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.


This study is summarised as evidence for the following.

Action Category

Remove or control predators using lethal controls: Tuatara

Action Link
Reptile Conservation
  1. Remove or control predators using lethal controls: Tuatara

    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.

    (Summarised by: Katie Sainsbury)

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