New research shows tuatara could be at risk from the same rodenticides that are used to protect them from rats.
Tuatara populations on offshore islands have benefited from anticoagulant poisons to kill rats, which eat their young and compete for food.
However, research on four dead captive tuatara by scientists showed they were likely exposed to a common rodenticide, brodifacoum, suggests they are also susceptible to such poisons, a statement from the Science Media Centre said.
It was likely the tuatara ate small rodents or bugs that had fed on the bait.
Massey University professor in wildlife health Brett Gartrell, said the research would have implications for both the tuatara, and how to care for them.
"It suggests that tuatara are susceptible to anticoagulant poisoning from brodifacoum and this has implications for both the captive management of tuatara, but also the use of rodenticides in tuatara habitat ...
"Brodifacoum is a widely used poison to control rats and mice in New Zealand, and we need to take care in its application to ensure that native wildlife are not affected."
University of Auckland school of biological sciences Prof James Russell said Brodifacoum was a powerful toxin that prevents blood clotting, and this study presents evidence of it causing harm to tuatara.
"This is important in New Zealand where little is known about the impacts of toxins such as brodifacoum on reptiles, even though New Zealand is a biodiversity hot spot for reptiles with over 100 endemic species," he said.
"Indiscriminate use of toxins can cause unintended harms, as was certainly the case here. However, toxins are also important in managing threats to reptiles — the greatest of which is introduced rodents.
"Almost certainly the use of brodifacoum in this case was ongoing and eventually building up to a lethal dose in the tuatara.
"It is for this reason that many pest controllers are shifting their long-term pest control strategies to use less toxic alternatives."
Victoria University of Wellington dean of the faculty of science and engineering Nicola Nelson said tuatara were expected to live to a ripe old age, so deaths were important to explain.
"Tools to manage the impact of introduced mammalian predators ... are crucial, but as pointed out by New Zealand Food Safety there is important work to do to consider access, use and impact."
— APL
