Dr. Jennifer Watts loves animals and math. In her work as the director of nutrition at the Chicago Zoological Society’s Brookfield Zoo, both passions are important.
There are about 3,000 animals at the zoo, all with unique personalities, preferences and dietary needs. To feed them the right macronutrients and micronutrients, it takes some serious math and planning. And to make sure the diet is appealing, diverse and enriches their lives—that's a labor of love.
This interview has been edited for clarity.
My job is to design the diets for our animals. I do the science behind the nutrition. We start by looking at what animals eat in the wild using information provided by researchers in the field. Based on that, we determine the composition and nutrient concentrations that will be the best for our animals’ health.
Take a nutrient like protein. We know that for primates, protein is about 10 to 15 percent of the diet. But for some species, like lorises or other animals that eat gums or nectar, the protein requirements might be a little bit lower.
There’s some trial and error. We'll try a diet and see how it works. If we see any deficiencies or anything that that’s not quite right, we make changes as we go. Zoo nutrition is still a new field, and we're learning every day.
Designing a Diet
When I started working here, the brown bears were not at an ideal weight. I needed to focus on reducing their weight. Part of the problem was that the proportion of nutrients in their diets wasn’t changing seasonally in the way that it would for bears in the wild.
In the spring, when brown bears come out of their dens, they eat a lot of grasses. They might eat the carcass of a calf if they find one, but their diet at that time of year has a lot of plant matter and very little protein.
As the year progresses, the protein content increases, culminating in the salmon runs where brown bears eat as much salmon as they possibly can to fatten up. Later in the fall, they focus on berries, nuts, seeds, grasses and other plants.
To reflect these seasonal changes, I put them on a diet that has changes in the proportion of nutrients—not just the overall volume of food—throughout the year.
Other animals have different seasonal changes in their diets. For hoof stock, we change their diet at the start of the wet season in May to simulate the way that wild grasses would be more lush and full of sugar during that time of year. For primates, we simulate a fruiting season by adding lots of fruit and vegetables to their diet, resulting in a 20 percent increase in calories during spring.
But there are limits. In the wild, bears eat fungus, so we were excited about giving them different mushrooms. But they were just kind of like, "no, no, don't want it." Same with cranberries. Sometimes it's like feeding 3,000 toddlers.