Regional Variation in Landscape Change and Agrochemical Exposure in a Grassland Breeding Shorebird Across North America

Widespread agricultural intensification across North America has raised concern about its impact on breeding bird populations. This process has accelerated globally over recent decades in response to increasing food demand and economic pressures, resulting in simplified landscapes and reduced diversity of crops and natural habitats. Pesticides are used intensively in modern agriculture, with millions of tons applied annually, and are likely to remain an important component of food production, raising concern about ongoing threats to natural resources. Whereas negative effects of agricultural intensification on population trends, species abundance, and avian biodiversity are well documented, effects on breeding grassland shorebirds have not been well studied. During the breeding season, Upland Sandpipers (Bartramia longicauda) are widely distributed across North America and inhabit a range of agricultural landscapes, making them an ideal model for evaluating the association between agricultural activities and grassland breeding shorebirds. The overarching goal of my thesis is to examine how Upland Sandpipers interact with agricultural landscapes during the breeding season by evaluating their responses to change in land use and their exposure to agrochemicals. Advancements in estimating species trends at breeding sites have allowed practitioners to examine regional drivers and associations of declines, ultimately allowing for targeted conservation efforts. In addition, new synthetic pesticides have been introduced that are gaining popularity in use across North America, and an updated assessment of exposure to agrochemicals in grassland shorebirds is needed. Understanding variations in risk from both land use change and agrochemicals across the breeding ground can help to inform conservation and management applicable to the Upland Sandpiper and other grassland breeding birds. Using large-scale citizen science data from 2012–2022, I modeled regional variation in trends of abundance for breeding Upland Sandpiper as a function of changes in estimated amounts of grassland and cropland across their range. Although range-wide trends were relatively stable (median annual change of −0.1%), results revealed regional variation in associations between population trends and changes in land use. I found that changes in grassland and cropland had a significant association with population trends at 45% and 22% of locations where population trends were estimated, respectively. Responses to the decline in grassland cover were variable across the breeding range but generally followed my predictions as the majority of locations (59%) experienced a decline in grasslands and an associated decline in breeding abundance. Additionally, the effect of cropland change was generally consistent with the prediction that increasing cropland cover was associated with more negative trends, though the magnitude of this relationship varied geographically. These findings suggest that the effects of grassland loss and cropland expansion were spatially variable, highlighting that conservation strategies should be spatially targeted rather than uniform across the breeding range. Using tissue samples collected across the breeding range allowed me to provide the first range-wide assessment of agrochemical exposure in breeding Upland Sandpipers. Analysis of plasma samples (n = 78) collected at breeding sites across Canada and the United States revealed frequent exposure to multiple chemical classes, including insecticides, herbicides, and fungicides. Each sample analyzed had at least one agrochemical detected, summing to 22 unique chemicals. I found regional variation in chemical richness for insecticide and fungicide chemicals, but not for herbicide chemicals. Samples collected in Saskatchewan consistently had the highest richness of chemicals across all 3 pesticide types (insecticides, herbicides, fungicides). The fungicide thiabendazole was highly prevalent in plasma samples analyzed (n = 55), but the concentrations in plasma samples did not vary by region. These results provide initial assessments of Upland Sandpiper exposure to contaminants on the breeding grounds, aiding in risk assessment for the species. Together, my findings demonstrate that Upland Sandpipers persist in agricultural landscapes but face dual pressures from habitat loss and agrochemical exposure. Sustainable management and effective conservation action for Upland Sandpipers will depend on coordinated efforts among producers, researchers, and conservation practitioners to balance agricultural productivity with sustainable landscapes for grassland birds.

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