Reproduction, growth and immune function: Novel insights in equatorial tropical birds

We aimed to determine variation in reproductive strategies, growth and immune function in lark species living in three climatically-distinct equatorial tropical environments. Environmental conditions and breeding in Red-capped Larks Calandrella cinerea within each environment were unpredictable and highly variable yearround. Among environments, environmental conditions and breeding differed, suggesting that these conditions vary over small spatial scale. In none of the three environments was nesting activity related to any environmental conditions, leaving an open question for further investigations, on what factors influence timing of reproduction. While nestling body mass and size at hatching were lowest in the most arid location, resources females allocated to their eggs, nestling in the most arid environment grew faster than in the other two wetter environments, pointing to the contribution of abundant food resources. Nestling growth in arid Kedong was better during periods when most individuals in the population were breeding and periods with more rain post-hatch, indicating better female body condition and food quality and quantity during these periods. Nitric oxide (NOx) in sympatric Red-capped and Rufous-naped Larks Mirafra africana and NOx in Red-capped Larks increased during chick-feeding, indicating the species’ capacity to maintain reproduction and immune function concurrently. Co-occurrence of high NOx and higher average maximum temperature (Tmax) during breeding in Red-capped Larks suggest that patterns of NOx may have responded to patterns of breeding or to changes in the high Tmax and that higher Tmax may have provided an environment for development and reproduction of pathogens that in turn triggered the elevation of NOx.