Homecoming at Hamilton Zoo for Stanley Island tuatara

It has been a homecoming of sorts for four juvenile Stanley Island tuatara who arrived back at Hamilton Zoo last week after leaving the facility nine months ago as eggs.

The eggs were laid in January by one of Hamilton Zoo's mature female tuatara, and were the first to be laid at the facility since 2001.

Hamilton Zoo director Stephen Standley said the arrival of the eggs earlier this year was exciting for staff who had just about given up hope of seeing any more tuatara eggs laid at the facility.

"The small group of tuatara that we have at Hamilton Zoo were all taken off Stanley Island, off the Coromandel Peninsula, in the early 1990s, prior to rats being eradicated from the island. Since then we have been attempting to breed these reptiles with limited success as they are believed to be very old.

"In 1997 we had four juvenile tuatara at Hamilton Zoo and then one each year from 1999 through to 2001 – Each of these tuatara have been released on to Stanley Island once they have been big enough to fend for themselves," he said.

After failing to produce any tuatara eggs for several years, in 2006 Hamilton Zoo swapped its two male tuatara with males from Auckland Zoo. Three years on, an x-ray confirmed that the exchange had been a success and that one of the facility's female tuataras was carrying eggs.

"In February we sent the eggs to Victoria University in Wellington for incubation. Two were incubated under higher temperatures and hatched as males in June, while the remaining two were incubated under lower temperatures and hatched as females in July," said Mr Standley.

The four tuatara arrived back at Hamilton Zoo last Thursday and are now on display in the facility's reptile house. They are expected to remain at Hamilton Zoo for about six years, until they are big enough to be released on to Stanley Island.

About tuatara:

Tuatara are slow breeders which mate in summer and lay eggs the following summer, before hatching the next spring or summer depending on temperature and weather conditions. Eggs are able to be incubated faster under artificial conditions with constant temperatures. Because males are produced from eggs that are incubated in warmer conditions and females from eggs incubated in cooler conditions, there are concerns that global warming will result in significantly more male tuatara than females.

Despite being legally protected since 1895, tuatara populations are continuing to decrease.