SAN DIEGO -- A trainer at the San Diego Zoo lost part of his finger to a chimp Wednesday.

A coworker of trainer Mike Bates said the two of them were doing a medical check on pygmy chimps known as bonobos Wednesday morning.

He said when Bates pointed at a chimp named Ikela to give the all clear that she was OK, the chimp bit off the tip off his finger.

Bates told a San Diego newspaper he must have gotten his hand too close to the chimp's mouth.

Later, zoo workers noticed the finger tip in the middle of a cage.

They signaled for another chimp named Lana to retrieve the finger.

As soon as the second chimp handed over the fingertip, she was rewarded with raisins.

Bates has 22 years of experience at the zoo.

Bates told the paper he was lucky the finger was still in tact and that the chimp didn't think it was food.

Bates had the fingertip reattached and has a 70 percent chance that it will heal, according to the paper.

Bates is expected to return to work next week.

Zoo officials theorized that Ikela, the 15-year-old chimp who did the nipping, might not have been feeling well.

Ikela is pregnant and could have been annoyed or tired by extra monitoring due to her pregnancy.

The picture of Ikela that is shown at the park reads, "Ikela is always pushing the limits of good behavior."

The caption for Lana, who rescued the finger, reads, "She has a strong bond with her caretakers."

According to the San Diego Zoo, bonobos are members of the great ape family, along with gorillas, orangutans, and chimpanzees.