"We need to find the mothers as soon as possible," Nathan tells the Wall Street Journal.
"The longer we wait, the more difficult it will be for the mothers and the babies to bond because of too much human contact. In a group [of elephants], there is not only the mum but also aunties and sisters who look after baby elephants. So why were this babies abandoned?"
Search teams have searched for elephant herds in the vicinity where the calves were found, but have so far been unable to find any.
Pygmy elephants, native to Borneo, are a critically endangered species, number as few as 1,500 -- adding extra urgency to ensuring these two members of the latest generation are returned to the wild.