Blue tits use selected plants and olfaction to maintain an aromatic environment for nestlings

Animals use the chemical compounds of plants as a defence mechanism against enemies, and sometimes use olfaction to discriminate and select the chemical plant substances. Some birds bring to the nest plant material that has volatile compounds that protect the host and their offspring against parasitic organisms. Here we show that blue tits on the island of Corsica (Parus caeruleus ogliastrae ) adorn their nests with fragments of aromatic plants. These plants have chemical compounds that are used by humans to make aromatic house cleaners and herbal medicines. We also show that individual blue tits maintain an aromatic nest environment when offspring are raised, using odour cues to determine the frequency with which they replenish the nest with fresh plant material. We provide an exceptional example of the ecologically relevant use of olfaction by birds under natural conditions. To our knowledge, we present the first experimental demonstration that a free-ranging animal makes use of smell to maintain an aromatic environment for offspring with plants, supporting predictions of the nest protection hypothesis.