The objective of this project is to use tree swallows (Tachycineta bicolor) to understand the ecological risk posed by per- and polyfluoroalkyl substances (PFAS) at selected Department of Defense (DoD) sites in the mid-Atlantic region of the United States. This study will fill data gaps on effects of PFAS on birds, especially those with high exposure potential, like aquatic insectivores. This project will include delineation of exposure pathways and quantifying effects, if any, on ecological receptors.

Technical Approach

Due to tree swallows now being widely used to quantify distribution and effects of local surface water and sediment contamination, they are an ideal model species to use in this context. Study populations can be established at specific locations of interest by deploying nest boxes in suitable habitats. Because tree swallows feed near those nest boxes (within 400 meters (m) of emergent aquatic insects), residues in their tissues reflect sediment contamination for bioavailable chemicals of concern. Additionally, data are now available on exposure and effects of various chemicals of concern, including PFAS, in tree swallows at more than 100 locations across North America.

Twenty tree swallow nest boxes will be attached to posts in proximity to suitable habitats at up to three DoD locations in the mid-Atlantic area. DoD locations will include former Naval Air Station (NAS) Joint Reserve Base Willow Grove (n = 3 sites), where swallow work is ongoing, and possibly Patuxent River NAS in Maryland and Joint Base McGuire in New Jersey. Like Willow Grove, other DoD installations may need multiple sites to adequately characterize PFAS exposure, depending on the size and extent of the potential impact. As nesting is being initiated, nest boxes will be visited regularly (approximately weekly, but occasionally more often) and reproductive data collected according to standard operating procedures. Reproductive data will include the number of eggs laid, number of eggs that hatched, and number of fledglings. Reproductive data will be compiled using estimates of daily nest and egg survival. At appropriate times, a sample of eggs will be collected under appropriate federal and state permits for chemical analyses. Unhatched eggs may also be collected. The eggs will be stored in a refrigerator and then processed before being analyzed for a suite of chemicals of concern by a contract laboratory (SGS Axys, Inc.). Additionally, a few 12-day-old nestlings will be collected from each nest box for analytical chemistry and a suite of bioindicator responses such as ethoxyresorufin-o-deethylase (detoxifying liver enzyme), thyroid hormone levels, oxidative stress measurements, and genetic damage assessments among others.

Perfluorinated substances (n = 33) will be analyzed in tree swallow tissues (eggs and nestling carcasses), as well as, in one or two composite stomach contents that represent what nestlings are being fed. The sampling targets will be 10 egg samples and 10 nestling samples per site. While PFAS are the primary chemicals of concern, a small number of nestling carcasses (5 per site) will also be analyzed for a standard suite of organochlorine chemicals, polychlorinated biphenyls and their livers will be analyzed for trace elements (n = 15) to understand exposure to other possible chemicals of concern. A nearby reference location (Patuxent Wildlife Research Refuge, Laurel, Maryland), will also have samples analyzed for PFAS (n = 5 per matrix) for comparative purposes and to serve as the baseline for biomarker analyses. Two levels of effects will be assessed. At the population level, reproductive effects measured as percentage hatching and daily probability of nest success, will be assessed relative to PFAS and other chemical exposure in eggs. Biomarker responses, which are indicative of whether exposure exceeds thresholds necessary to elicit physiological responses in individual birds, will be compared to normal responses. 


This study is scalable, and no-observed-adverse-effect level/lowest-observed-adverse-effect level (NOAEL/LOAEL) results are transferable to other DoD locations. The results will allow the DoD to further understand the ecological risk posed by PFAS to avian species in the mid-Atlantic region of the United States. Results will contribute to assessments of the health of the target ecosystems and will provide a baseline for future trend and/or geographic analyses at DoD locations. (Anticipated Project Completion - 2024)