What senses do birds use? Obviously, they use hearing and sight—after all, they sing and often have colorful plumage. But what about the sense of smell? For a long time, it was thought that olfaction played no role in birds. In recent years, however, a number of papers have emerged that refute this assumption—including research that looks at the secretion from the preen gland that birds smear on their feathers several times a day. Scientists, including some from Bielefeld University, have investigated what changes there might be in the composition of the secretion and what role smell plays in this. Their study was published on 6 February in the journal Biological Reviews.