When scientists discovered seven baby Bell's turtles in a batch of six eggs they had incubated they were initially stumped.
University of New England PhD candidate Louise Streeting said she was sure there was a clerical error, but couldn't have been happier to be proved otherwise.
'When we investigated more closely we realised two babies had come out of the same egg — they're half the size of their siblings," she said.
The twins form part of a repopulation project that is boosting numbers of the endangered Bell's turtles in NSW Northern Tablelands.
It has put close to 3,000 Bell's turtles put back into the local ecosystem.
But twins have never been produced during the project, and with very little literature available, Ms Streeting said new ground has been broken.
"There has been no research into twins in Bell's turtles, there has been very little research into twins across turtles in general," she said.
"It's 1-in-3000 eggs, which is very rare — at least for us."
"Twins do occur across other species of turtles, for example the alligator snapping turtle [has] three sets of twins per 1,000 eggs."
During their time in the lab, the Bell's turtles are assessed, with their measurements and weights recorded, before they are released into waterways on a private property on the Severn River at Glen Innes.
"The twins are half the size of their siblings, but they are doing really well — hopefully they will catch up with their siblings as time goes by," Ms Streeting said.
Future of the program
Last year, researchers released 1,500 Bell's turtles into the Northern Tablelands, but the team had to take a more conservative approach for this year's release.
The Gwydir and Namoi river systems were a particular focus last season and were "plentiful" with adult female Bell's turtles to be induced to lay eggs.
However, the focus is now at Glen Innes Severn, where there are fewer adult turtles to induce.
"Unfortunately, this means we can't harvest as many eggs, but obviously makes it extremely important for this water system," Ms Streeting said.
High rates of predation on nests by wildlife make the program integral to the population of endangered Bell's turtles.
"The turtles are endangered because foxes are raiding more than 97 per cent of turtle nests each year," Ms Streeting said.
"In particular, the population in the Severn and other waterways."
With her PhD graduation just around the corner, Ms Streeting is hopeful the program can continue to grow.