Male European Starlings Use Odorous Herbs as Nest Material to Attract Females and Benefit Nestlings

Abstract

Male European starlings (Sturnus vulgaris) use odorous herbs as green nest material. They show these plants to females to catch their attention before they incorporate them into their nests. Nestlings reared in nests containing herbs carry fewer bacteria, have higher haematocrit levels and more basophile leucocytes, and have a higher fledging weight than those reared in nests without herbs. The incubation temperature is higher in nests with herbs than in herbless nests. Females are attracted by herb nests and herb nests provide energy-saving benefits to incubating females. In choice experiments, starlings employed olfaction to select nest herbs, using innate information and experience acquired as nestlings to identify odours. Measures of head space air in starling nest boxes revealed an increase of volatile substances during the nestlings phase. Manganese-enhanced resonance imaging of the olfactory bulb of starling showed that the neural correlates of olfactory sensitivity change seasonally. Starlings can only discriminate odours during the reproductive season. The association between odour perception and reproductive behaviour suggests that increased testosterone production, related to the increasing photoperiod in spring, may guide these seasonal changes. The size of the olfactory bulb but not its ability to discriminate was affected by testosterone implants in the non-reproductive season.