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Forest Forensics

Watch out, Canis lupus, a.k.a., the wild grey wolf. Lizzy Berkley knows what you’re eating. Sure, you may have licked the blood of your last prey from your paws, but there’s a record of your deed that you can’t hide.

For Berkley, a graduate student in forest and wildlife ecology, the proof is in the fat.

Typically, researchers have a difficult time telling exactly what wild animals eat. They can make guesses by picking through scat for bits of bone and fur or examining the stomach contents of dead animals. But even these methods still reveal only what an animal ate last night. What about last week? Or last month?

Berkley and her advisor, forest and wildlife ecology assistant professor Tim Van Deelen, are experimenting with a new strategy, which traces telltale signs of an animal’s diet in its fat cells.

Every animal species has a unique mix of fatty acids. When one animal eats another, some fatty acids from the prey are deposited largely intact into the fat tissue of the predator, creating a signature that can be identified through lab analysis. Since fat accumulates over time, researchers can learn about what an animal has eaten for the past six months by studying a sample of its fat.

Guided by Van Deelen, Berkley is using the model to assess the diet of wild wolves in the upper Midwest. The goal is to determine how much wolf diets vary according to the prey available: Do they eat mostly what’s around and plentiful, or do they prefer a particular species if they can find it? Answers to these questions might help wildlife managers protect livestock or fragile populations of elk or moose.

Berkley’s model actually begins with dogs. To create a baseline for how prey species’ fatty acids show up in wolf tissue, she prepared hundreds of what she calls “fatsicles”—Dixie cups full of frozen moose, beaver, deer and cow fat—and fed them to a group of Inuit sled dogs, closely related to wolves. She then took tissue samples from the dogs and analyzed them using a gas chromatograph, an instrument that separates organic material into component compounds.

Next, she’ll compare those profiles to fat samples collected from wild wolves trapped throughout the Midwest. Since she knows what the dogs ate, she hopes that similar fat signatures will create a record of what the wolves have been feasting on, as well. It’s kind of like CSI: Up North, except smellier.