A related research theme is our aim to come to terms with the evolutionary consequences of seasonal challenges faced by vertebrate organisms, challenges that have frequently been invoked as explanations for variation in the pace of life among bird species. However, knowledge of seasonal patterns of self-maintenance and disease, and understanding of the underlying physiological mechanisms are incomplete. We aim to examine how birds cope with environmental challenges through an integrated study of energetics, corticosteroid response, and immune function in contrasting environments that have different seasonal patterns, resource availability and risk of disease (e.g. in a comparison of desert, tropical and temperate environments, or in a comparison of marine and freshwater wetlands), or during contrasting seasons (summer versus winter). Seasonally recurrent stressors include food and water shortages combined with high ambient temperatures during desert summers, and food shortages and low temperatures during temperate zone winters, whereas tropical areas may be benign year-round.
During the most stressful season free-living birds may be forced to compromise immune function because they cannot meet energy requirements. In temperate and tropical terrestrial and in freshwater environments, an inability to maintain high levels of immune function may be more detrimental because the risk of disease is higher than in high arctic or desert habitats or marine environments. In the tropics, year-round high levels of immune function may be achievable because stressful seasons are absent. The studies will include comparative work on shorebirds (see next theme), larks from desert, tropical and temperate areas, and other passerines. We aim to use a combination of laboratory and field energetics, corticosteroid analyses, and recently developed immunological assays for field studies to assess overall levels and seasonal patterns of metabolic rate, corticosteroid response, and immune function in both study systems.
