Biologist Erick Greene has been taking blood samples from Osprey chicks in northwest Montana for years. Ospreys eat fish, so toxins in the water become concentrated in their bodies. Their blood offers a window into how pollution moves through the food chain. Finding high mercury levels in Osprey chicks helped Greene trace the toxin’s source.

Hear more about how Montana’s Ospreys are persisting despite pollution on the Threatened podcast.