Early exposure to a bacterial endotoxin may cause breeding failure in a migratory bird

Early life conditions may have important long-term consequences on viability and reproduction. Considering their pervasiveness in natural environments, parasites play a crucial role in determining life-histories of hosts, by negatively affecting their performance and imposing fitness costs. Here, we tested whether exposure to a bacterial endotoxin (lipopolysaccharide, LPS) during the nestling period influenced breeding performance at sexual maturation of a small passerine bird, the barn swallow (Hirundo rustica). Three out of 56 LPS male nestlings were recruited in their breeding site, compared to six out of 51 controls. None of the LPS recruits was observed to breed or to pair with a female, while all control recruits bred successfully, with a mean seasonal breeding success of 6.4 fledged offspring. In addition, LPS recruits were captured later than controls. Despite the low sample size, our results suggest that exposure to a bacterial endotoxin during the critical phase of development may negatively affect reproductive success in these short-lived migratory birds, possibly via delaying timing of moult and arrival from wintering grounds.