Abstract
Shorebirds have experienced some of the steepest population declines among all types of birds in North America. Declines are especially pronounced in birds that occur in
agricultural areas due to habitat loss, pesticide use, and wetland degradation. The Lesser
Yellowlegs (Tringa flavipes), a declining shorebird species that frequently uses agricultural
areas to rest and refuel during long annual migrations, has lost nearly two-thirds of their
population since 1970. Threats in one of their most critical stopover sites—the North
American Prairie Pothole Region—have the potential to impact a large proportion of their
population. In this region, agriculture and drought may reduce wetland quality, reduce prey
availability, and impair refueling. However, the relative effects of these threats on shorebirds
are not well understood.
We evaluated how agriculture and drought in the Prairie Pothole Region influence
wetland quality and shorebird refueling. Over two spring and two fall migration seasons
(2021-2023), we surveyed wetlands, measured shorebird body condition, sampled aquatic
macroinvertebrates (2023 only), and collected environmental and shorebird plasma samples
for neonicotinoid and other pesticide analyses. We used these data to investigate whether
agriculture, insecticides, and drought reduce prey availability or impact body condition in
Lesser Yellowlegs and in other shorebird species that also use Prairie Pothole wetlands.
Chapter 1 investigates the effects of agricultural cropland cover and drought on
shorebird body condition, macroinvertebrate biomass, and macroinvertebrate diversity.
Wetlands surrounded by high cropland cover and those without vegetation buffers (≤ 50 m
wide) had lower macroinvertebrate biomass compared to wetlands with more grassland
cover. Shorebirds captured at wetlands with high cropland cover had smaller pectoral
muscles (Lesser Yellowlegs only) and higher β-hydroxybutyrate levels (all species
combined), indicating increased fat metabolism. During drought conditions, shorebirds had
lower fat scores and higher uric acid levels (Lesser Yellowlegs only), indicating increased
protein catabolism, along with reduced body mass across all species. Macroinvertebrate
diversity was higher in wetlands with more shoreline vegetation cover. Shorebird refueling
improved in more isolated wetlands (lower β-hydroxybutyrate levels in Lesser Yellowlegs)
and with more exposed shoreline (lower uric acid levels across all species combined). Our
results suggest that maintaining native grassland buffers (≥ 50 m wide), sparsely vegetated
margins, and portions of exposed shorelines unobstructed by dense vegetation in wetlands
may enhance stopover habitat quality for shorebirds in agricultural landscapes.
Chapter 2 documents the extent to which neonicotinoid insecticides and other
pesticides in the Prairie Pothole Region influence shorebird body condition,
macroinvertebrate biomass, and macroinvertebrate diversity. We also identified conditions
and shorebird species most at risk to neonicotinoid exposure. Neonicotinoids were detected
in 21% of shorebird plasma samples, 24% of water samples, and 7% of macroinvertebrate
samples in 2023 (when all three sample types were collected). We detected 18 additional
pesticides in 46% of macroinvertebrate samples. Most neonicotinoid and pesticide
concentrations in wetlands and in shorebirds were low. However, we documented a few
notably high concentrations in shorebird plasma even during drought and before spring
planting (periods when exposure is expected to be relatively low). Shorebirds with
neonicotinoid detections in their plasma had marginally lower triglyceride levels, suggesting
a potential negative effect on fat deposition. Higher neonicotinoid concentrations in water
were associated with lower macroinvertebrate diversity. Macroinvertebrate biomass and all
other shorebird body condition metrics were not associated with neonicotinoids. Spring
migrants that used wetlands with high surrounding cropland cover had a higher likelihood of
accumulating neonicotinoids, particularly during years with late spring snowmelt. Our study
provides evidence of neonicotinoid accumulation in shorebirds and highlights the need for
continued research on contaminants in wetlands used by migrating shorebirds. Overall, our
findings suggest that intensive row-crop agriculture and drought hinder shorebird refueling
indirectly by reducing prey availability and directly by impacting some metrics of body
condition, with neonicotinoids posing a potential added risk to prey diversity and shorebird
refueling that requires more study. Maintaining grassland buffers around wetlands may help
mitigate these effects and improve stopover habitat for shorebirds in agricultural landscapes.