Background: Bobolink, a threatened species in Ontario and Canada, breed in hayfields, pastures, and other grasslands. Many songbird nests fail to fledge young and the frequency of fledging typically varies across land cover types and uses. Additionally, characteristics of fields (e.g., size), field surroundings (e.g., field edges), and landscape characteristics (e.g., percent of nearby forest cover) may influence nest survival because these characteristics can be associated with nest predators, food availability, and other reasons for nest failure.
Project work: In collaboration with Professor Erica Nol, graduate student Monica Fromberger, and others in the Nol lab at Trent University, we studied Bobolink nest survival to learn about the environmental conditions that provide the highest probability for nests to survive. We monitored nests over two years in various land cover types (i.e., restored grasslands, fallow fields, pastures, late-cut hayfields) and pooled our data with nest data collected previously by BECO and the Nol lab to model Bobolink nest survival across typical environmental conditions on farms and conservation lands.
Results from a nest survival analysis of 463 Bobolink nests, led by Monica Fromberger, showed that two variables, date of season and cattle stocking rate, were important predictors of nest survival. Nests were less likely to survive as the breeding season progressed and nests in grazed pastures were negatively impacted by the intensity of grazing. Other variables, including land cover surrounding fields, field use, field area, and distance to forest edge, were not found to be associated with nest survival in our analysis.
Conservation implications: Our study demonstrates that various types of fields (restored grasslands, fallow fields, pastures, late-cut hayfields) have potential conservation value for Bobolink because nest survival did not vary across these field types. To support Bobolink nesting success in pastures, keeping cattle stocking rates low is important. Because our study showed that nest survival decreases across the season, actions that support early-season nesting attempts should have conservation value (e.g., minimizing inadvertent destruction of early-season nests in managed grasslands). Additionally, our results did not identify field size as an important factor affecting nest survival; therefore, small fields may have conservation value for Bobolink. However, the density of breeding birds, which is also important for focusing conservation efforts, may vary by field size and field type.
Conducted in collaboration with Trent University.
Project dates: 2017 – 2019
Funding: Support for this project was provided by the Government of Ontario, Mitacs, Echo Foundation, the CICan Natural Resources Internship program, and individual donors.