Rate of constitutive innate humoral immune development in Leach's storm petrel (Oceanodroma leucorhoa) chicks is negatively correlated with growth rate

1 Using a simple technique for assessing constitutive innate immune function recently adapted for use in wild populations, we characterize changes in avian immune system development by repeated measurements of individuals over the period of nestling growth in a wild population of Leach's Storm-Petrels (Oceanodroma leucorhoa). 2 We measured levels of natural antibodies (NAb) during the early, middle and late phases of storm-petrel development and related these levels and NAb rate of change to mass and wing length growth. We used natural variation in nestling growth to assess the influence of nutritional status on the development of innate immunity. 3 NAb levels increased over the first 50 days of chick development; however, rate of increase was inversely proportional to wing growth. 4 Initial titre levels were inversely proportional to rate of change in NAb levels over the first 50 days of immune development. This suggests that individuals with low initial NAb levels accelerate immune development to reach adult levels, whereas individuals with high initial levels do not. 5 As in previous studies, our results demonstrate an inverse relationship between growth rate and development of components of the avian immune system. While such a relationship is consistent with the idea that immune function development involves trade-offs, the processes involved are more complex than simple energy allocation.