Story highlights The panda's paternity is unclear

Mei Xiang gives birth after quick labor, zoo officials watch for second

Giant pandas are one of the world's most endangered species

Zoo Atlanta welcomed the first ever panda twins in July

There's a new panda in Washington.

Officials at the Smithsonian's National Zoo confirmed the arrival of a cub on Friday for Mei Xiang following a quick labor.

DC's new celebrity resident was about the size of a butter stick and zoo officials said it appeared to be doing well, as was mom, who was cradling it in her den.

"This is a very delicate time for us. We're still on the lookout for a possible second cub," the zoo's director, Dennis Kelly, said at a news conference.

There was a 50% chance of a twin being born later Friday or early on Saturday.

A healthy little panda would be extra special because the female cub that Mei Xiang delivered nearly a year ago died within days. A lack of oxygen due to underdeveloped lungs was determined as the cause.

Zoo officials said they were pleased and hopeful things would work out this time, and they even brought in an expert from China to help out.

"After our last experience, and this is such a small cub, I am not going to relax," Kelly said. "We're gong to be tense for the next two or three months. We have high hopes."

It will take two to three weeks to know the sex of the cub and zoo officials won't name it for 100 days, following Chinese tradition.

Conceived through artificial insemination, it was the third pregnancy for Mei Xiang, 15. The National Zoo says the cub's father is either their own Tian Tian, 15, or the San Diego Zoo's Gao Gao, who is about 23.

All three pandas are on loan from China.

Mei Xiang and Tian Tian are already the parents of Tai Shan, who was born in 2005 and now is in China, the native region for the endangered animals.

American zoo officials are consulting with their Chinese counterparts about panda reproduction and ways to encourage newborns to thrive in captivity.

The giant panda is one of the world's most endangered species, with an estimated 1,900 in existence.

Among pandas born in captivity, about one in four males and one in four females die in the year following birth, according to the National Zoo.

The twins were the first for Lun Lun, who has two other offspring at that zoo, and were the product of artificial insemination as well. Their father is Yang Yang, also a resident.

National Zoo experts began watching Mei Xiang a couple of weeks ago, and the anticipation peaked once she became restless and began cradling objects.