Habitat destruction and the direct exploitation of species often occupy center stage in discussions of biodiversity perils. However, indirect harms, such as that posed by nitrogen pollution, remain underappreciated and poorly understood despite playing a key role in species declines. The mechanisms of nitrogen's impacts are diverse and often involve hard-to-pinpoint chains of causality. For this episode, we're joined by Dr. Dan Hernandez of Carleton College and Dr. Erika Zavaleta of the University of California, Santa Cruz. They and their colleagues recently conducted a survey of 1400 species listed under the US Endangered Species Act, finding a total of 78 that face known hazards from excess nitrogen. They describe their findings here.