BENEFICIAL EFFECTS OF CLOACAL BACTERIA ON GROWTH AND FLEDGING SIZE IN NESTLING PIED FLYCATCHERS (FICEDULA HYPOLEUCA) IN SPAIN

Abstract

Effects of bacteria on avian hosts in the wild have received little attention until recently. Whereas the pathogenic effects of bacteria are well known, positive effects of symbiotic bacteria are more rarely considered. Nestling growth has important repercussions for offspring fitness in avian populations and may be affected by microbial colonization of the gut. Enterococcus faecalis is a common opportunistic pathogen, whereas E. faecium has been used as a growth promoter because it interacts competitively with pathogenic bacteria, E. faecalis included. We followed the growth in tarsus length and mass of 18 Pied Flycatcher (Ficedula hypoleuca) broods. Chicks were weighed and measured on days 4, 8, 10, and 13 after hatching. On day 13, wing length was also measured and cloacal swabs were taken of two chicks in each brood for detection of enterococci. In all, the methods used allowed us to detect six species of bacteria among a possibly much richer community. Most chicks had E. faecalis, whereas E. faecium was less prevalent. There was a negative association between scores for E. faecalis and for the rest of the species pooled. The presence of E. faecalis showed no detectable association with nestling mass or size at any age, whereas the presence of the other species showed significantly positive associations with mass and size on day 13, but not before. Presence of E. faecium on its own was positively associated with nestling mass and size shortly before fledging. E. faecium may act as a growth promoter in the wild through its competitive interactions with facultative pathogenic bacteria. The presence of some microbes are critically important in avian growth and development.