Utility companies use turkey vultures to sniff out gas pipeline leaks

Natural gas is odourless, so pipelines are laced with ethyl mercaptan, the same compound that gives rotting meat its smell. Turkey vultures can detect that odour from the air at just a few parts per trillion, so engineers began flying over pipelines and marking exactly where the birds circled or landed — pinpointing leaks invisible to any instrument of the time.

— Kenneth E. Stager, The Role of Olfaction in Food Location by the Turkey Vulture (Cathartes aura) — Contributions in Science, Los Angeles County Museum, No. 81, 1964