Leon Vlieger in The Inquisitive Biologist:
To successfully navigate their world, organisms rely on numerous senses. Birds are no exception to this; and yet, for a long time, people have been convinced that birds cannot smell. This came as a surprise to evolutionary biologist Danielle J. Whittaker. Given that smell is effectively chemoreception (the sensing of chemical gradients in your environment) and was one of the first senses to evolve, why would birds have no use for it? The Secret Perfume of Birds tells the story of 15 years spent investigating the olfactory capabilities of birds and provides an insider’s account of scientific research.