For nearly 20 years, Robin Baird has been following killer whales, trying to figure out what they eat. At first, he would look to see what was in their mouths as the whales feasted on fish near the surface. But then he and his colleague, Brad Hanson, started looking for more subtle clues in their flukeprints — the orbs of placid water that appear on the surface when a killer whale dives into the sea, or flicks its tail underwater. In or around these flukeprints, you can find fish scales and fecal matter, which provide a treasure trove of information.

“If they’re catching things near the surface of the water, it’s much [easier] to be able to document than if they’re capturing things at depth,” Baird, a research biologist at Cascadia Research Collective, told Mongabay in an interview. “What the fecal samples do is they show … a higher proportion of things like lingcod and halibut and sole flounder [that] are caught deeper in the water column and less likely to be brought up to the surface.”