Feeding zoo animals is kind of like feeding toddlers. At least, that’s how Dr. Jennifer Watts, director of nutrition for Chicago’s Brookfield Zoo, describes her job. “All of our animals are individuals and they all have their own taste preferences,” she says. “We know what meal is the best food to feed [them], but getting them to actually eat it is the challenge.” Along with her small staff, Watts works to prepare and deliver food in bulk for 3,000 vertebrate animals of 300 different species. Zookeepers typically weigh each individual meal and feed the animals. Her job is rare—she is one of about 20 zoo nutritionists in the country. Breakfast is typically served before the animals go out on exhibit for the day, followed by some food while out on exhibit, and an evening meal after they return to their night area. But the actual feeding schedule is very species-dependent.

Tigers eat a complete meat beef product with vitamins and minerals. However, they fast once a week to simulate a day without a kill in the wild. One day includes a meal of bones to help with dental health. While tigers eat twice a day, the four-foot-long Gaboon viper only eats once a week or so. Her diet? A medium-sized rat. Figuring out what each animal likes to eat is a process of trial and error and some animals have strong opinions.

“We know that our old silverback gorilla hates grapefruit,” Watts says. “He would get really angry if we tried to give him or the group grapefruit.”

When an animal comes from a different institution, it may be used to a different diet. One warthog previously ate only apples and carrots before coming to Brookfield Zoo where he was introduced to new foods like broccoli, peppers, and grapes. “It took him a little while to get used to the idea he was getting all this variety, and he took to most of the stuff, but it’s a process,” Watts says.

One recent to the animals’ diets introduction was mamey sapote, a Central American fruit. “It was kind of hit and miss,” she says. “Some of our animals don’t do well with novel foods and you have to give them a couple times to get used to it because they’re very used to what they normally get. Some took to it right away and some needed a couple days to try it out. Each individual has taste buds and preferences.”

The zoo goes through 85,000 pounds of meat each year, 250,000 pounds of fish, 330,000 pounds of fresh fruit and vegetables, and 14,000 eggs. The nutrition team chops 400 pounds of carrots and sweet potatoes each week and prepares 140 pounds of fruit salad a week, among many other duties. Much of the food comes from a company that also supplies Chicago restaurants.

“Everything we feed out is human quality,” Watts says. “We don’t feed out anything we wouldn’t eat ourselves.”

Surprisingly, many familiar human snacks  are on the menu. Keepers scatter and hide Cheerios, Rice Krispies, pasta, and popcorn through some exhibits so animals like primates and bears become more engaged with their environment. Some primates even receive Flintstones and gummy multivitamins.

“People would often be surprised at how much stuff we have on our shelves that you see in a grocery store,” Watts says.

But not everything can be found at the grocery store. During the summer, a local utility company trims trees near transmission towers and power lines, fills large trucks with the trimmings, and delivers this “browse” to the zoo twice a week. “All sorts of herbivores eat the browse, like giraffes, rhinos, okapi, gorillas, orangutans, reindeer, hyrax, camels, kangaroos, [and] gerenuk,” explains Watts.

Carcasses are another non-standard item. Keepers feed African wild dogs, big cats, and wolves the bodies of deceased animals like goats and deer so they can exhibit natural pack behavior.

“We do that more for the social aspect of it,” she says. “If we allow them that opportunity to showcase and enforce where everyone’s social standing is, we actually get less aggression because they have the opportunity to put each other in place and reinforce the social structure of the pack.”

While every animal has their food preferences, Watts ensures each animal eats multiple food items in case their current favorite, like a particular kind of fish, becomes unavailable.

“If we had animals only eating herring and for some reason the catch that year was terrible, we’d have a problem trying to transition our animals over to other fish,” she says. “If we have them normally eating two or three different types of fish, we’d have no issue with switching them around… and not being in a lurch with not having a diet item on hand.”

Just in case, Watts has two vendors for each product, so she can have a steady supply if there’s a problem with one vendor. When your job is to essentially feed 3,000 picky toddlers every day, being prepared comes in handy.