Starling males select green nest material by olfaction using experience-independent and experience-dependent cues

Male European starlings, Sturnus vulgaris, incorporate fresh volatile herbs into their nests. This behaviour is related to courtship but also benefits the nestlings. We tested in aviary experiments whether males select aromatic plants using olfaction and whether they depend on experience with nest odours they encountered as nestlings. We scented nests of wild starlings with milfoil, Achillea millefolium, a preferred nest plant of the starlings, and other control nests with vanilla. Fledglings from both nest types were hand-reared and tested the following year in dyadic choice experiments for their odour preference. Males from both milfoil- and vanilla-treated nests preferred milfoil scent when they had the choice between milfoil-scented versus vanilla-scented or versus unscented leaves. However, when they had to choose between vanilla scent and no scent, males from vanilla-treated nests chose vanilla scent but males from milfoil-treated nests did not discriminate. The disinterest of vanilla-inexperienced males in vanilla-scented leaves (when milfoil scent was lacking) and the preference for it in vanilla-experienced males implies learning during the nestling period. Because males discriminated between leaves of the same plant species looking the same but scented with different odours and because males without milfoil experience instantly preferred milfoil odour, we conclude that starlings use olfactory cues to select green nest material following an olfactory pattern designed prior to birth which may be supplemented by learning early in ontogeny.