PORTLAND, Ore. -- Zookeepers and veterinarians at the Oregon Zoo were on alert Friday after elephant Rose-Tu went into labor early.

Photo courtesy Oregon Zoo

Rose-Tu

Rose-Tu's due date was mid-September so the first signs of labor were somewhat of a surprise to watchful keepers.

"With a 22-month gestation period, it is not unusual to have dates vary by a month or more," said Mitch Finnegan, the zoo's lead veterinarian.

Finnegan believes the birth may take place sometime within the next 24 hours.

"The birth of a new baby is the most enriching thing that can happen in an elephant herd," said Mike Keele, the zoo's deputy director, and the Association of Zoos and Aquariums' Species Survival Plan coordinator for Asian elephants.

"If all goes well, and we hope it will, the rest of the herd will tightly bond and protect the baby as if it were their own. There are some risks associated with being a first-time mother, but we're hopeful," he added.

There is a 30 percent infant mortality rate among captive Asian elephants.

"There can be complications to both mother and calf," said Keele. "A calf may be stillborn or get lodged in the birthing canal. We'll be monitoring her pregnancy very closely."

If the birth is successful, the baby will be Rose-Tu's first, and it will be the 28th baby elephant born at the Oregon Zoo.

Tusko is the father.

Baby elephants normally weigh 225 to 325 pounds; however, when Rose-Tu was born she weighed 184 pounds. Elephants are able to stand within 45 minutes of birth.

If healthy, the new baby could be in the elephant viewing room, ready to see zoo visitors in a couple of days.

However, Finnegan warns that these things are on their own schedule.

Rose-Tu, born Aug. 31, 1994, was the last elephant born at the zoo. She is a popular elephant within the herd and with her keepers. She is always looking to tease her herd mates and shares a strong friendship with Chendra, who is nearly the same age.

Rose-Tu is the second-smallest elephant in the herd, weighing about 7,600 pounds.

Tusko arrived at the zoo in June 2005 on a breeding loan. He has sired three calves in the past -- two while living in Canada and one in California.

In the fall of 2006, Tusko was introduced to Rose-Tu in hopes the two would make a love connection, zoo official said.