New Method Can Measure Naturally Occurring Element Exposure in Hummingbirds Without Harm

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Seventeen naturally occurring trace elements, including those associated with adverse health impacts when birds are exposed to toxic levels (iron, lead, mercury, selenium, zinc, cadmium, and arsenic) were measured in small birds without harm. The nonlethal method was developed for hummingbirds, with Anna's hummingbirds (Calypte anna) as a test species and can be more broadly applied to other hummingbird species.

Anna's Hummingbird (Calypte anna) Flying

Anna's hummingbird (Calypte anna) photographed mid flight. Anna's hummingbirds are year-round residents of California where samples were collected for this study.

(Credit: Robert D. McMorran, Ventura Fish and Wildlife Office, U.S. Fish and Wildlife Service. Public domain.)

Hummingbirds are sensitive avian pollinators whose diet is primarily nectar but also includes insects. These foods are known to be sources of naturally occurring trace elements. Some trace elements are necessary for biological function at low levels; however, avian exposure to toxic levels of trace elements has been linked to reproductive failure, impaired growth, and behavioral alterations.

Hummingbirds' small body size limits traditional sampling techniques, such as blood and other tissue sampling, to evaluate exposure to contaminants; therefore, scientists developed alternative non-lethal sampling, processing, and analytical methods that effectively measure trace element exposure in very small birds — Anna's hummingbird (Calypte anna).

These novel methods were used to measure trace element exposure in live and dead Anna's hummingbirds in three areas of the California Floristic Province (coastal, valley, and Sierra Nevada foothills). Small mass feather samples from live birds and feather and internal tissue samples from salvaged birds were tested for 17 trace elements. This study emphasized seven of the trace elements (iron, lead, mercury, selenium, zinc, cadmium, and arsenic).

The results of the environmental sampling indicated that Anna's hummingbirds were exposed to trace elements but further work is needed to determine if the exposures were harmful.

Hummingbirds are a widespread and abundant taxon in the United States that live and breed in diverse climates and habitats. They can be an important sentinel species due to their role in ecosystems as pollinators, as prey, and as a predators. This non-lethal method will be used in future studies as one of many tools that help scientists determine if hummingbirds are exposed to harmful levels of trace elements in the environment.

This study is part of a long-term goal of the U.S. Geological Survey (USGS) Environmental Health Programs to provide the science needed to understand the actual, as opposed to the perceived, risks that contaminant exposures pose to the health of fish, wildlife, livestock, companion animals, and humans.

Support for this study was provided by the USGS's Environmental Health Contaminant Biology Program, the University of California, DavisYolo Audubon Society, the Ron Magill Conservation Endowment, and the University of California, Davis School of Veterinary Medicine's Students Training in Advanced Research Program.

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