Collaborative Research: Energetic consequences of rain and nest structure for ecology and evolution of songbirds in tropical rainforests

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Rainfall varies extensively among biomes and over time with weather cycles like El Niño. Lab studies have shown that warm-blooded organisms lose heat at a more rapid rate when wet and must spend more energy to regulate body temperature. Effects of rainfall on energy expenditure in the wild is unstudied, but may critically affect reproduction and survival of organisms. Energy is often most limited to animals when trying to raise offspring, with the latter especially vulnerable to increased energy costs of wetting because of poorly developed fur or feathers. This project examines energy costs of rainfall to parents and their offspring in tropical songbirds. Tropical organisms provide an important test because they are thought to be sensitive to heat loss and thermal conditions due to the narrow temperature variation in the tropics. Also, rain is a prevalent feature in tropical rain forests (often 2 m per year). Investigations will examine energy expenditure of both parents and offspring on dry versus wet days and at nests where rainfall is experimentally modified. Measurements will be conducted across diverse species that differ in their behaviors, nest types and potential exposure to rain to advance understanding of the energetic costs and differential population vulnerabilities of species as a result of variation in rainfall. This work has important conservation implications because it identifies population sensitivities of endemic species in a biodiversity hotspot. In addition, many students from a variety of disciplines, including those outside of biology will be trained in the conduct of field work and scientific principles. Ecological and evolutionary influences of precipitation are poorly studied. Proposed work will significantly advance understanding of the energetic (field metabolic rates) and demographic consequences of variation in rainfall on coexisting songbirds in a tropical rainforest. These costs may be strongly expressed in tropical rainforests where rain is prevalent, thermal tolerances are narrow, and temperatures are often below thermoneutral levels. Yet, studies of the effects of rainfall and wetting on energetics, behavior and demography across diverse tropical species are lacking. The proposed work will use novel experimental and observational approaches to advance understanding of how nest structure affects energy use of parents due to heat loss under wet versus dry conditions. The proposed work will also elucidate how rain, temperature, nest structure, and parental behavior combine to affect energy expenditure of offspring and how energy is allocated to differing body components during growth. Finally, it will reveal demographic ramifications of the physiological costs of rain and nest structure to gain new insight into fitness consequences. Ultimately, this work will provide a new understanding of the influences of climate and nest structure upon heat balance and evolution of parental and growth strategies among diverse species. This work will also identify relative demographic sensitivities of species as a function of their nest types, ecologies and behaviors to aid prioritization schemes for conservation. A large number of undergraduate and graduate students, as well as a post-doctoral scholar, will receive training in diverse field methodologies and scientific principles.