Coping with uncertainty: Adapting to stochasticity in an unpredictable tropical environment

Birds adjust their phenotype in response to socio-environmental changes. To understand these adjustments, aseasonal tropical areas offer an ideal setting to tease apart effects of the environment and social interactions on life history of birds. In this thesis, exploiting a stochastic, aseasonal tropical environment, we investigate if/how weather, food availability and nesting intensity are related to nest success, and whether Red-capped larks adjust their phenotype through behavioural space use and physiological adjustments of body mass and immune function to adapt to the stochastic environment. Our results show that nest predation was the single most significant cause of nest failure, but the negative correlation of nest success with flying invertebrates and rainfall, proxies of increased food availability, pointed to incidental depredation. Secondly, the number of nests found per month (nesting intensity) was the main factor influencing the home range of birds. However, Red-capped larks decreased body mass with increased food availability independent of life history stage which suggests year-round food availability. This suggests birds opt for a lean mass under good conditions probably to counter associated negative costs of higher body mass. Lastly, immune function was better explained by socio-environmental factors, while life history stage played a minor role. The stronger influence of social-environmental factors may be due to the hypothesized higher parasite diversity and pathogen pressures in tropical areas compared to temperate regions. Our study underlines the relevance of conducting more studies in aseasonal tropical areas in order to disentangle socio-environmental factors that vary in an unpredictable and unsynchronized manner.