Bacteria on nestling skin in relation to growth in pied flycatchers

The association between skin bacterial communities and nestling growth is poorly understood. We estimated the abundance of heterotrophic bacteria on skin of nestlings and their association with growth in the pied flycatcher Ficedula hypoleuca. At two different nestling ages, we swabbed a delimited area of the naked belly skin of nestlings and measured them. Skin bacterial loads on day 13, but not on day 7, were positively associated with brood size and with nestling wing length. Larger broods develop in less hygienic conditions, which may stimulate bacterial growth. Skin bacteria may favor wing feather growth through competition with harmful bacteria, or faster feather growth may facilitate bacterial growth through the accumulation of remains on the skin surrounding growing feathers.