Environmental influences and early life experiences on immune function of the zebra finch (Taeniopygia guttata)

Understanding what drives variation in immune function has been a focus of avian eco-immunologists in the past few decades. I conducted several very novel experiments to investigate potential sources of variation. First, I assessed variation in innate and adaptive immunity during nestling rearing in adult zebra finches whilst experimentally manipulating the microbial load of the nesting environment. The primary immune response (adaptive) was much higher in birds attending dirty nests (higher microbial load) than clean nests, suggesting that the microbial environment upregulated the adaptive immune system. Despite differences in nest sanitation, constitutive innate immune function decreased in adults throughout the period of caring for their young, but was not affected by nest microbial load itself. Surprisingly, nest sanitation did not impact upon innate or adaptive immune function or growth in nestling zebra finches. Interestingly, the innate and adaptive immune measures tested were not fully functional at the time of fledging or even at 60 days,which may suggest that young altricial passerines may tolerate rather than defend against potential pathogens at that stage. Secondly, I investigated the development of innate immune function in juveniles that had been subjected to an experimental acoustic playback whilst they were embryos. Eggs exposed to incubation calls were fed more as nestlings and were heavier at 13 days of age. However, as juveniles (around 60 days of age), males were in poorer body condition than females but males had much better constitutive innate immune function, suggesting a trade-off between condition and immune function. Overall, these results collectively suggest that the microbial environment, and acoustic components of the rearing environment, can lead to variation in different facets of immune function. Studies investigating immune function in wild birds should consider these potential causes of variation to get an accurate representation and understanding of bird health and functioning.