Stoichiometry and Functioning
Birds are highly mobile, abundant, and metabolically active organisms, able to alter ecosystem structure and function through dispersion of nutrients they sequester and release. My current research examines drivers of variation in the body and waste stoichiometry (nutrient composition) of birds to underscore the mechanisms influencing how birds differentially mediate ecosystem processes. I hope to shed light on the importance of sustaining services that birds provide through their roles in biogeochemical cycling.
• Abraham, A., Duvall, E., Ferraro, K., Webster, A., Doughty, C., le Roux, E., and D. Ellis-Soto. (2022). Understanding anthropogenic impacts on zoogeochemistry is essential for ecological restoration. Restoration Ecology https://doi.org/10.1111/rec.13778
Sodium (Na) plays a critical role in the functioning of terrestrial ecosystems. Sodium is essential for animal growth and maintenance, but typically non-essential, and often toxic, for plants. As a result, most plants uptake Na passively, leading to low foliar Na concentrations in Na-poor ecosystems (e.g., non-coastal). This induces a unique stoichiometric mismatch between herbivores and their food that can lead to Na limitation. Our research seeks to understand the causes and consequences Na deficiency in herbivores, from individuals, to communities, to ecosystems at broad scales.
Mineral licks and Na cycling in western Amazonia
The western Amazon is one of the most Na-poor regions in the world. High precipitation, temperatures, and humidity lead to rapid nutrient leaching, while it’s position relative to the Andes and ocean impedes external Na input. Consequently, plant consumers (herbivores) face challenges in obtaining sufficient Na within their natural diet. While Na shortfall has been shown to constrain smaller organisms (such as termites) and their ecosystem impacts (such as decomposition), large herbivores can seek out mineral licks, areas where animals visit to ingest Na-rich soil and water. While the importance of Na as a driver of mineral lick-use and ecosystem functioning is increasingly understood, the subsequent role of large herbivores in Na cycling remains overlooked. Quantifying such roles is essential to understanding anthropogenic impacts on ecosystem functioning through changes in the environment (e.g., oil extraction in western Amazonia) or animal populations themselves (e.g., game hunting). My research addresses these questions through spatially-explicit model simulations, biotic and abiotic field measurements, and study of human practices in the western Amazon.
• Duvall, E., Griffiths, B., Clauss, M., and A. Abraham (In review). Allometry of sodium requirements and mineral lick use among herbivorous mammals.
Foraging behavior and preferences
Birds lay eggs, and eggs-shells are made almost entirely out of calcium carbonate (CaCO3); yet the diet of many non-carnivorous birds lacks sufficient calcium for egg-laying. Nestlings also need additional calcium for rapid skeletal growth during the breeding season. In order to meet these calcium requirments, birds must locate and consume calcium-rich material within their respective environments. My goal is to better understand the ecological interactions of birds and calcium in the wild, including how these interactions vary by species, calcium sources, season, and habitat. The research currently takes place in Ithaca, NY, using camera trapping techniques to record information on calcium foraging behaviour and preferences.
Riverbird responses to dam removal
Dam removal has become a priority for the conservation of freshwater biodiversity globally. My research has focused on two of the largest dam removals in history on the Elwha River, WA, examining changes in the abundance and distribution of river-dependent birds before and after dam removal. Only 4 years after dam removal, species are returning to upstream river sections and nesting density of nearly all species has increased. Our work also suggests that riverbird responses can be effective indicators of restoration progress. I am now examining bird responses to the removal of smaller, more pervasive stream barriers in tributaries of the Hudson River, NY.
• Duvall, E. and McLaughlin, J. (In preparation). River-dependent birds measure restoration following Elwha dam removals
• Buchanan, B., Sethi, S., Cuppett, S., Jackman, G., Lung, M., Zarri, L., Duvall, E., et al. (2022) A machine learning approach to identify barriers in stream networks demonstrates high prevalence of unmapped riverine dams. Journal of Environmental Management https://doi.org/10.1016/j.jenvman.2021.113952
Bald eagle responses to declining salmon carcasses
Each winter, thousands of Bald Eagles from across western North America migrate to Pacific Northwest rivers to feed on the carcasses of post-spawning chum salmon. However, declining salmon populations and impacts of climate change are reducing the availability of salmon carcasses as a wintering food source for eagles. My research has focused on eagles ability to adjust to these impacts, specifically by redistributing to non-river habitats. My results suggest that the utilization of agricultural areas may be an important survival strategy for eagles as chum salmon carcasses continue to decline. Preliminary results of our follow-up study have shown that dairy farms are especially important, and that by feeding on dairy farm discards, eagles may actually provide services to farmers without conflict.
• Duvall, E. (2022). Spatiotemporal responses of bald eagles to changes in salmon carcass availability in the Pacific Northwest. Northwest Science Vol 95. https://doi.org/10.3955/046.095.0306
• Duvall, E., Schwabe, E., and K. Steensma (2023). A win-win between farmers and an apex-predator: investigating the relationship between bald eagles and dairy farms. Ecosphere https://doi.org/10.1002/ecs2.4456