Kate Karpuk would wake up at all hours of the night, get out a bottle and warm it to the perfect temperature.

But Karpuk doesn't have children. Instead, the 32-year-old Union, New Jersey, resident was hand-feeding Cassie, a baby groundhog who calls the Staten Island Zoo home and whose famous dad, Chuck, has rubbed elbows with mayors.

Hand-rearing these baby wild animals, often in the zookeepers' own homes, has become common, helping the animals become comfortable with humans at an early age so they can be used for educational purposes later on. But the practice comes with its own challenges, and keepers have to balance getting attached to their unconventional pets with preserving the animals' wild instincts.

"I don't have children, but I kind of think of them [as that]," Karpuk said. "You do have to do your research because they are wild animals. It's not like a puppy. You fall in love and it's hard not to treat them as a part of the family because essentially they are. But ... they are the zoo animals."

Karpuk and her partner, 23-year-old Nicole Kovara, raise several animals for the zoo. They tend to bring home animals that will eventually end up in the children's zoo or as ambassador animals that visitors can see as part of a hands-on learning experience.

Dr. Noha Abou-Madi, a clinical associate professor and section chief of zoological medicine at the Cornell University College of Veterinary Medicine, said it is always best to raise animals with their own kind, but there can be benefits to giving certain babies human contact. It is not recommended with certain species, like deer or antelopes.

"There's an advantage of hand-raising these animals if they are not going to become aggressive: they recognize people as their companions," she said. "In terms of a zoo animal, there's an advantage of these animals becoming comfortable with humans."

But nothing that zookeepers can do will fully domesticate certain species, Abou-Madi said.

"If you look at tigers, for example, if you hand-raise them they may be more comfortable coming to the gate to greet you or interact with you," Abou-Madi said. "But if you go in the gate they may attack you. In terms of that behavior, it doesn't remove it."

In an effort to mimic the animals' natural instincts of having two parents, Karpuk and Kovara share joint custody of the zoo's beaver, Ashokan, who was found abandoned in Ithaca and rescued in May along with her sister, Tayanita. Beavers don't tend to do well without their biological parents and, unfortunately, Tayanita died a few days later.

"They don't do so great when they're babies on their own without their mothers. And it's very hard to raise a wild animal in captivity," Kovara said. "It's definitely hard because you have to play mom or dad. You're there at all times: you're the caregiver, you're there to comfort them when they're scared, you're there to feed them. It is like taking care of your own child except it's an animal."

They said Ashokan is now thriving.

"It's essential that she has two parents and not like three, not four, not five, not one," Karpuk said. "We're mom and dad."

Hand-raising an animal can sometimes become necessary for its survival. Javier Alvarez, the hospital manager and avian collection manager for the Staten Island Zoo, did just that when the parents of a Nicobar pigeon weren't taking care of their egg. The Nicobar pigeon, which is part of the Association of Zoos and Aquariums' Species Survival Plan Program, hatched in July.

"For the first three or four days they have to be fed every two hours from 8 o'clock in the morning until 10 o'clock at night," Alvarez said. "It was kind of fun for me anyway, but I actually ended up sleeping over at the hospital for about three or four days."

Kovara is also helping to raise Bintu, an 8-month-old porcupine. Bintu, who was born at a Tennessee zoo, spent about four months in Kovara's home but recently started living at the zoo again.

"We try to keep it as normal as possible, so if they were actually in the wild this is how would be for them," Kovara said. "So with Bintu, as well, I have about three or four other co-workers who have come in contact with him a lot and that's because he would normally live in a burrow with about four other porcupines: his parents, his siblings. They stay in a group, that's what he's used to. That's what his natural habit is, to live with a family."

This is one of many steps the zookeepers take to maintain the animals' wild instincts, while giving them an education in how to act with humans.

"The main reason we do all this hand-raising is to teach the public," Karpuk said. "If you come and you visit the zoo, it's really great if you can pet a sloth, if you can touch a porcupine, if I can sit here and talk to you all day about a groundhog and let you touch the groundhog. People form a bond with those animals just by doing that."

The Staten Island Zoo:

614 Broadway, West Brighton, Staten Island;

(718) 442-3100;

Open 7 days/week from 10 a.m. to 4:45 p.m.