Parasite defence in birds: the role of volatiles

European starlings (Sturnus vulgaris) mix fresh herbs, preferably species rich in volatile compounds, into their drynest material. By investigating air samples from starling nest boxes, we found that nestlings and their parasites encountervolatile compounds such as sabinene, myrcene, limonene, phelandrene and ocimene, some of them with medicinal properties.We compared mite load and nestling condition in experimental nests with and without herbs. Herbs had no effect on thequantity of nest-dwelling ectoparasites, but a significantly inhibiting effect on bacterial growth in late nests. There was also atendency for mosquitoes to visit nests containing herbs less often than nests without herbs. Chicks that fledged from herb nestswith higher body mass had more red blood cells and differed in some immunological parameters from controls. Herb chicks alsohad more basophil leucocytes, but fewer lymphocytes than nestlings from nests without herbs. More yearlings from herbnests were identified and showed interest in nest boxes in their first year as adults. The better condition of herb chicks may havebeen due to plant compounds that stimulate elements of the immune system to help nestlings cope better with harmful impactsfrom parasites and other stressors. Apart from their effects on parasites and nestlings, volatile compounds in herbs that arecarried into the nests by males may also play a role in mate attraction.

Helga Gwinner, Silke Berger, Acta Zoologica Sinica 52(Supplement): 280-283, 2006