Infant golden lion tamarins cling to their mother shortly after birth, then transfer to their father. (National zoo photo)

Two monkeys from an endangered species were born last week at the National Zoo, but one of them died on Tuesday, the zoo said.

It appeared, the zoo said, that one of the two golden lion tamarin infants “fell off one of its parents this morning.”

The two were born June 29. The surviving monkey was doing well, the zoo said.

Keepers had seen both of the newborns being carried by their parents, the zoo said. The parents are named Izzy, and Mo. Izzy is the mother and Mo is the father.

Last week the zoo said that since birth the two infants had clung to the back of their mother. But, the zoo said, they would transfer soon to their father. Mo would carry them “at all times” except when they are nursing, the zoo said.

It was not made clear Tuesday which parent was carrying them when the fall occurred.

“Golden lion tamarins have high infant mortality rates, with approximately half of infants dying before they reach 1 year old,” the zoo said last week. It said Tuesday that keepers would continue close monitoring of the survivor.

Once only 200 golden lion tamarins were left in the wild, the zoo said, but conservation measures and breeding programs had increased the wild population to 3,200. However, the zoo indicated that golden tamarins remain endangered.

They are native to South America and threats include habitat loss and collection for the illegal pet trade, the zoo said.