Each juvenile bear that arrives at the zoo gets assigned a color, and zookeepers mix the glitter into their meat patties. That way, when they examine the resulting poop, they can connect it to a bear.
"With food colorings, you know, it was either red, which made it look like the animals were eating beets or had some kind of internal problem, or it just got metabolized," Petersen explained. But even glitter that's safe to eat will stay intact in a polar bear's digestive system.
This might already be done with animals at your local zoo. You probably wouldn't know it, because (disappointingly) the practice doesn't turn enclosures into glittering rainbows.
"People aren't usually close enough to see poo sparkling in the sunshine," Petersen said with a laugh.
But in this case, all that glittering poop yields a goldmine of data: Researchers start by analyzing the stress hormones of young bears during their first few months at the zoo, looking for spikes that might indicate they should treat the cubs differently.
"We can see how the things we do affect stress hormones that appear in the scat, and that tells us what we can do better the next time we get new cubs," Petersen explained.
Petersen and other scientists track the bears' hormonal levels using the scat. It's much less invasive than collecting the same information using blood draws – and easier to accomplish when studying wild bears. By monitoring hormonal levels and fluctuations in bears living in captivity, the scientists can figure out what benchmarks to look for when they collect scat from bears in the wild.
"We could look at progesterone and see if they’re pregnant females, or look at testosterone to see if it’s a young or mature male," Petersen said. One of his long-term projects involves collecting hair and scat from wild bear caves, checking to see whether mothers teach their female cubs to return to the same spot.
"That could give us a better sense of how important those habitats are," Petersen said. Habitat loss is the biggest threat to polar bear survival these days. Ice loss out on the sea has them going on long, grueling swims to hunt for food, and the bears have to make it to caves on land to give birth. Human habitat destruction or a lack of ice could keep polar bears from getting back to the same spots their mothers gave birth in — so if the bears really do go looking for specific caves, their reproduction could be interrupted.
Petersen hopes that the research will benefit captive and wild bears alike — and that he won't run out of colors. Already, one of the bears has a combination of two colors of glitter in their diet. And some colors don't work very well.
"We had to get rid of white glitter, because they just couldn’t distinguish it . . . especially in winter when there are ice crystals on the poo," he said.
But since the bears' scat is only measured until they reach sexual maturity, he thinks they have enough wiggle room left on the color spectrum.