Systematic Approach to Understanding Tree Swallow Health in the Great Lakes Region—Science to Inform Restoration

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Four papers by U.S. Geological Survey (USGS) scientists document tree swallow (Tachycineta bicolor) chemical exposure, physiological responses, and reproductive success in the Great Lakes region. These studies were designed to understand if there are health threats to swallows from contaminant exposure, and to provide resource managers with information about the actual as opposed to the perceived risks of exposure, which is needed to inform restoration efforts.

Scientist preparing samples in a laboratory

U.S. Geological Survey (USGS) scientist preparing samples for analysis of protein levels to normalize results from oxidative stress bioassays.

(Credit: Natalie Karouna-Renier, U.S. Geological Survey, Patuxent Wildlife Research Center. Public domain.)

Contaminant (primarily polychlorinated biphenyls, polycyclic aromatic hydrocarbons, dioxins, and a variety of pesticides) occurrence in harbor and stream sediments in the industrialized portions the Great Lakes has been well documented. However, the link between the contaminants and health threats to individual organisms or entire populations is not well defined.

USGS Environmental Health Teams conducted research relevant to understand health threats to an indicator species (tree swallows—Tachycineta bicolor) in the Great Lakes Region of the United States. Tree swallows are an ideal test species because they nest throughout the region, feed locally on aerial stages of aquatic insects, and as a result have close ties to sediment contamination. This research was done in partnership with Great Lakes Restoration Initiative.

The Initiative began in 2010 with a renewed effort to assess and restore, where needed, contaminated harbors and rivers across the Great Lakes at 31 specific Areas of Concern (AOCs). AOCs, designated under the Canada Great Lakes Water Quality Agreement, include watersheds or portions of watersheds that exhibit conditions sufficient to cause any of 14 specific impairments of beneficial use. The ultimate goal is restoration of the AOCs to a level similar to surrounding non-AOCs so they can be delisted.

A typical tree swallow studied by the scientists

A typical tree swallow (Tachycineta bicolor) studied by the scientists.

(Credit: Thomas Custer, US Geological Survey. Public domain.)

The results from a series of USGS studies during 2010-2014 are documented in four papers outlining contaminants in birds and their eggs, biomarkers of contaminant exposure (ethoxyresorufin-O-dealkylase (EROD) activity, chromosomal damage, and six measures of oxidative stress), and reproductive success. Results indicate that adverse effects were restricted to relatively few birds at a few sites in the Great Lakes region.

  • Tree swallow nestlings and eggs had low levels of contaminants that were similar to or lower than surrounding non-AOC locations.
  • Less than 25 percent of the sites studied had birds with physiological responses that would indicate exposure to chemicals at concentrations that would require detoxification or indicate oxidative stress.
  • At those sites with biomarker responses, polycyclic aromatic hydrocarbons were reported to be the primary contaminant driver.
  • At the sites with the lowest reproductive success, dioxins, furans, and polycyclic aromatic hydrocarbons were found to be the primary contaminant drivers.

While this research was done at AOCs in the Great Lakes, the reproductive and physiological responses deduced from this study are applicable to other contaminated locations throughout the Nation.

This study is part of the science done by Environmental Health Mission Area Programs to provide answers to questions about the actual risk, not the perceived risk, of contaminants and pathogens in the environment.

This study was supported by the Great Lakes Restoration Initiative (GLRI) and the USGS Contaminant Biology Program.


Custer, C.M., Custer, T.W., Etterson, M.A., Dummer, P.M., Goldberg, D., and Franson, J.C., 2018, Reproductive success and contaminant associations in tree swallows (Tachycineta bicolor) used to assess a beneficial use impairment in U.S. and binational Great Lakes’ areas of concern: Ecotoxicology, v. 27, no. 4, p. 457-476, doi:10.1007/s10646-018-1913-9.

Custer, T.W., Custer, C.M., Dummer, P.M., Bigorgne, E., Oziolor, E.M., Karouna-Renier, N., Schultz, S., Erickson, R.A., Aagaard, K., and Matson, C.W., 2017, EROD activity, chromosomal damage, and oxidative stress in response to contaminants exposure in tree swallow (Tachycineta bicolor) nestlings from Great Lakes Areas of Concern: Ecotoxicology, v. 26, no. 10, p. 1392-1407, doi:10.1007/s10646-017-1863-7.

Custer, T.W., Custer, C.M., Dummer, P.M., Goldberg, D., Franson, J.C., and Erickson, R.A., 2017, Organic contamination in tree swallow (Tachycineta bicolor) nestlings at United States and binational Great Lakes areas of concern: Environmental Toxicology and Chemistry, v. 36, no. 3, p. 735-748, doi:10.1002/etc.3598.