Background: Located northwest of Orangeville, Ontario, the Grey Dufferin Community Pasture is an impressive block of grassland, nearly 600 acres, which provides grazing opportunities for cattle from local farms, supporting approximately 600 beef cattle through rotational grazing each spring and summer. It also provides a significant amount of wildlife habitat.
We studied three species of grassland birds that nest in the community pasture: Bobolink, Eastern Meadowlark, and Savannah Sparrow. All three species have steeply-declining populations in Ontario and rely on agricultural grasslands, including pastures, for nesting habitat. Unfortunately, grazing during the nesting season can have unintended consequences on ground-nesting birds. Nests can be impacted directly, when trampled by cattle, or indirectly, when the removal of vegetation causes exposure to predators. Grazing can also result in the displacement of birds from their breeding territories if vegetation is no longer suitable for nesting.
Project work: Using transect surveys, spot mapping of territories, and nest monitoring, our goal was to assess the distribution and abundance of Bobolink, Eastern Meadowlark, and Savannah Sparrow and how cattle grazing in the community pasture impacted abundance and nest success.
In 2019, we conducted transect surveys across the pasture to collect preliminary data on grassland bird species distribution and abundance before grazing began and in the middle of the nesting season, once many of the fields had been grazed. Following the last round of transect surveys in June, we conducted targeted spot mapping to assess breeding in a sample of Bobolink territories in grazed and un-grazed fields. We also collected vegetation data in June to assess characteristics such as height, density, and ground cover composition in grazed and un-grazed fields in order to better understand the relationship between vegetation characteristics and field use by the birds before and after grazing occurs.
In 2020, we repeated transect surveys, Bobolink spot mapping, and vegetation surveys. Additionally, we monitored Eastern Meadowlarks and Savannah Sparrows. To monitor Eastern Meadowlarks, we used spot mapping and nest monitoring, visiting each of the ~20 territories across the pasture once per week throughout the breeding season to record behaviour and nesting status. For Savannah Sparrows, we spot mapped a sample of territories in mid-June in grazed and un-grazed fields and we monitored nests we located opportunistically.
Overall, in both 2019 and 2020, few Bobolink remained in fields after the first grazing occasion and they appeared to stay only in fields where vegetation was not grazed heavily. In contrast, the number of Eastern Meadowlark territories monitored in 2020 did not change due to grazing. Some territory boundaries shifted and some pairs moved due to grazing, but most territories remained throughout the breeding season and pairs attempted to re-nest after nest failures due to grazing or predation. Savannah Sparrows also continued to be abundant across the pasture after grazing occurred.
Conservation implications: We are now analyzing data collected at the community pasture to improve our understanding of the impacts of rotational grazing on nesting grassland birds and support conservation efforts for these species. We will also provide information and recommendations to the Grey Dufferin Community Pasture managers about possible stewardship actions that could be implemented to support nesting grassland birds.
Project dates: 2019 – 2020
Funding: This project has received funding support from the Government of Ontario. Such support does not indicate endorsement by the Government of Ontario of the contents of this material. Additional support provided by The McLean Foundation, the Helen McCrea Peacock Foundation, and individual donors.
Hundreds of acres of grassland at the Grey Dufferin Community Pasture provide habitat for many grassland species, including birds at risk.
Photo: Xuan Zhang
An Eastern Meadowlark nest in the Grey Dufferin Community Pasture.
Females alone build nests, weaving dried grasses and forbs to create cup nests, frequently with a roof. Nest construction typically takes about one week.
Photo: Zoé Lebrun-Southcott