Rare Eastern Black Rhinoceros Is Born At Chicago's Lincoln Park Zoo

(CNN) -- A rare baby rhino was born after over a year of waiting for its big arrival.

On Sunday, the mother, Kapuki, 13, gave birth to the as-yet unnamed baby rhino at Lincoln Park Zoo in Chicago.

"After 15 months of pregnancy and a relatively quick labor, we're excited to announce Kapuki gave birth!" the zoo announced on Twitter. "Kapuki's maternal instincts kicked right in and she has been seen tending to the calf."

Animal care and the veterinary team are monitoring Kapuki and the calf from a remote camera to give them time to bond privately. They will only intervene if they see a crisis developing. The animals will not be visible to the public until further notice, the zoo told CNN.

It's not yet been determined if the calf is a male or female.

The first 48 hours of a calf's life are critical, the zoo said. The baby rhino has already reached important milestones including nursing and standing. The calf stood up at only 53 minutes of age, an impressive feat, even for a rhino. The zoo says it remains "cautiously optimistic."

The birth doesn't just mean there will be another cute animal to see at the zoo. It also represents the "preservation of a critically endangered species that faces a lot of challenges," Curator of Mammals Mike Murray said in March when the zoo announced Kapuki's pregnancy.

The eastern black rhinoceros is a critically endangered sub-species of the black rhinoceros, with the population of black rhinos only at 5,000-5,400. The number of black rhinos dropped by 98% between 1960 and 1995, according to the World Wildlife Fund. Since then, their population has made a huge comeback, thanks to conservation efforts.

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