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The rock-climbing brothers (31) came to New Zealand from their home town of Ventura on a working holiday, but ended up living and working in Milford Sound, exploring New Zealand's natural playground.
While working for Southern Discoveries, they heard about the work the company had been doing with the Fiordland Conservation Trust and Department of Conservation to establish a sanctuary in the Sinbad Valley, at the base of Mitre Peak.
Over the summer the brothers and other Southern Discovery volunteers worked with Doc to cut access tracks in the valley and climb previously inaccessible rock faces to establish the numbers and condition of a range of wildlife - including the rare and endangered Sinbad Gully skinks.
Doc now had more data on several of the most rare Sinbad skinks thanks to the brothers making several three-day trips into the valley.
They also located more than a dozen other lizards, among them Mahogany skinks and Cascade gecko.
"We've both got a deep respect for the environment, so when we heard Southern Discoveries was looking for volunteers to help with gecko and skink research on our days off, we put our hands up," Dave said.
"Sinbad Gully's the most special place I've ever been.
"We fly in by helicopter because that's the only way to access this remote valley, then climb up to a spot where we set a number of small cylindrical mesh traps along a rock wall with some bait in them to attract the geckos and skinks.
"Later in the day while the sun's still on them we go back up to check the traps then gently bring them back to the valley floor for the Doc people to measure, check and photograph them before re-releasing them where we found them."
Joe said working with Doc had been an educational experience and he and his brother were delighted to have put their rock-climbing skills to such good use.
"These skinks are tiny, beautiful creatures, so being involved with this project means my experience of New Zealand has been nothing short of magical."
Both said it was a privilege and an honour to work with Doc to help preserve species.
"I think we've done something that makes a difference, and I love telling people about what were doing and why," Dave said.
The Sinbad Gully Project was a result of the collaboration of Southern Discoveries, the Fiordland Conservation Trust and Doc which had a long-term commitment to ridding the valley of predators.
Ongoing donations from Southern Discoveries was also helping to establish a pest control programme.