The endangered Sumatran orangutan infant at New Orleans’ zoo is being bottle-fed because his mother wasn’t producing enough milk. The still unnamed baby was being tube-fed as well, but the tube was removed Jan. 13, Audubon Zoo spokeswoman Annie Kinler Matherne said Wednesday.

The great apes with long red hair are considered critically endangered by the International Union for Conservation of Nature. Threats to the Sumatran species include hunting and the destruction of the forests and peat swamps where they spend nearly all their time in trees.

Twelve-year-old Menari gave birth to the baby on Christmas Eve; a twin brother was stillborn. Days later, the baby was showing signs of weakness and lack of nursing.

Veterinarians examined Menari, a first-time mother, and discovered the lactation problem.

Since then the infant has had round-the-clock care from zoo staffers wearing furry vests that the baby can cling to. Until the feeding tube was removed, their duties included making sure he didn’t pick or pull at the thin tube inserted through his nose.

He’s been eating well and now weighs 1.98 kilograms (4.35 pounds), Audubon Nature Institute Vice President and general curator Bob Lessnau said in a statement sent by Matherne.