Wildlife researchers in California had a mystery. On March 17, 2017, residents in a part of the town of Modesto reported a number of dead goldfinches (Spinus tristis) along the street. After conducting necropsies, researchers at the California Department of Fish and Wildlife’s Wildlife Investigations Laboratory found the birds died from ingesting a nicotine-derived pesticide called Imidacloprid. The day before, city workers had applied the pesticide to the base of trees along the street, although they had reportedly followed the directions on the packaging. So why did the birds die? Researchers determined they likely ingested fallen elm seeds that had been contaminated during the application. The event revealed a previously unidentified risk, they concluded. If seeds or insects are present during application, they could represent contamination threats to wildlife, even if the pesticide is being applied correctly.