The positive influence of wetlands on reproductive success and body mass in an aerial insectivore is more pronounced in intensively cropped agroecosystems

Weather and land-use changes can act in complex ways to affect species’ annual demographics and distributions. Biodiversity and agriculture are frequently intertwined, where climatic conditions, such as flooding and drought, may be exacerbated by intensive agricultural practices. Understanding how climate change and agricultural land use influence avian populations is key to retaining biodiversity in working landscapes. Here we examined a large dataset of breeding Tachycineta bicolor (Tree Swallow) in Canada’s Prairie Pothole Region (PPR) across eight years at eight sites representing a gradient in agricultural intensity and wetland availability, for a total of 42 site-years. We analyzed the influence of agricultural land use, wetland availability, and seasonal temperature on Tachycineta bicolor reproductive success and body mass, while testing for potential interactive and curvilinear effects. As predicted, fitness measures were negatively affected by agricultural intensity; specifically, clutch initiation date was later and nestling body mass was lower at cropped versus non-cropped sites. Also, as predicted, interactions revealed that the beneficial effects of wetland availability were more pronounced at cropped sites. Associations between temperature and fitness measures were less clear but suggested the potential for detrimental effects of temperature extremes that might also depend on agricultural intensity. Our results contribute to a growing body of literature demonstrating the negative impact of intensive cropping practices and the importance of retaining natural and semi-natural habitats, including wetlands, in working landscapes to conserve biodiversity and buffer against temperature extremes and future climate changes.

Methods
Data were collected on Tachycineta bicolor from 2012 to 2019 at eight sites (n = 42 site-years) east of Saskatoon, Saskatchewan, Canada (52.1579°N, 106.6702°W) to analyze the influence of agricultural land use, wetland availability, and temperature on reproductive success (clutch initiation date and fledging success) and adult and nestling body mass. Refer to the associated manuscript for specific details on the calculation of agricultural land use (crop category), wetland availability (pond area), and temperature (mean daily maximum temperatures) variables.