Background: Populations of songbirds that nest on the ground in grasslands are declining across North America. Conversion of grassland to other land uses and changes in grassland management to maximize forage production for livestock are likely the primary causes of population declines in grassland birds. Established stewardship practices, such as delaying grazing until after birds finish nesting, benefit nesting birds, but often result in reduced agricultural production, hindering uptake by farmers.
Project work: We are using existing data to assess the conversion of grassland to other land cover types in southern Ontario over the last decade. We are identifying how much grassland has been lost and gained, where these changes have occurred in the landscape, and what land cover types are replacing grassland. Additionally, we are assessing if grassland conversion is associated with particular characteristics of the landscape, such as price of land, soil type, and distance to urban areas and roads.
In spring and summer of 2021, we conducted field research on farms in Grey County to increase our knowledge about stewardship implementation and conservation opportunities for grassland birds.
To quantify the occurrence of grassland birds, we surveyed hayfields and pastures for birds in late May, largely before agricultural activity began in these agricultural grasslands. In early June, we provided reports to farmers detailing the locations of grassland birds on their farm and individualized recommendations for grassland bird stewardship meant to fit with farm management.
We also collaborated with farmers to implement and monitor impacts of light grazing in spring on the nest success of Bobolinks, the most common grassland bird species at risk in the region. Light grazing of pastures in spring by livestock is intended to balance conservation and farming goals. Light grazing in late May, after Bobolinks begin nesting, may inadvertently destroy nests, but if enough vegetation remains and the pasture is then rested for at least 40 days, Bobolinks have sufficient time to renest and raise young. We monitored Bobolink nests in lightly-grazed pastures and undisturbed hayfields and pastures for comparison.
While monitoring Bobolink nests, we conducted a pilot project on nest microclimate in grazed pastures and undisturbed fields. We hypothesized that grazing might impact nest microclimate because some of the vegetation that provides shelter and thermoregulation is removed. At each nest where we sampled microclimate, we placed a pair of data loggers to record temperature every 5 minutes inside the nest cup and ambient temperature just outside the nest.
Conservation implications: We are currently analyzing grassland conversion data. Identifying regions with high grassland conversion might help identify target areas for conservation of particular grassland bird species. If some landscape characteristics are associated with grassland conversion, these variables may help us predict where grassland is likely to be converted in the future, informing conservation planning.
We are also analyzing field data to assess the impacts of light spring grazing on nesting success of Bobolinks and nest microclimate. If light spring grazing has minimal impact on Bobolink nest success, this may be a feasible management strategy for more farmers than deferred grazing. If grazing influences nest microclimate, future research may be warranted to assess impacts on nesting, including if adults vary behaviour to adjust for changes to microclimate.
Project dates: 2020 – 2021
Funding: This project received funding from the Government of Ontario. Such support does not indicate endorsement by the Government of Ontario of the contents of this material. Funding was also provided by the Ontario Trillium Foundation, ECO Canada, the Government of Canada’s Canada Summer Jobs program, Colleges and Institutes Canada, The McLean Foundation, S. M. Blair Family Foundation, and individual donors.
A male Bobolink perched on a bamboo stake placed ~2 metres from his nest to mark its location for monitoring.
Photo: Xuan Zhang
A Bobolink nest with a temperature logger. We placed temperature loggers in nests and just outside of nests to assess nest microclimate in grazed and ungrazed fields.
Photo: Zoé Lebrun-Southcott
A flock of more than 60 Bobolinks lined the fences of this hayfield where the harvest was delayed to provide grassland birds a chance to nest successfully. This photo was taken on July 16, 2021.
Photo: Zoé Lebrun-Southcott