At the recent Ontario Soil and Crop Improvement Association Annual Conference, two researchers from Bird Ecology and Conservation Ontario – Andrew Campomizzi, Research Scientist and Zoé Lebrun-Southcott, Executive Director and Wildlife Biologist – shared some staggering statistics on bird population declines.

Since 1970, nearly 3 billion North American birds have vanished – a 29% population decline.  Grassland birds appear to be suffering the most significant losses with 720 million lost since 1970 – a 53% population decline (Rosenberg, Kenneth et al. Decline of the North American Avifauna. October 4, 2019. <>).  Grassland-dwelling birds such as Savannah sparrows, bobolinks and eastern meadowlarks have been hit especially hard.

The research Campomizzi and Lebrun-Southcott presented focused on bobolink populations in eastern Ontario.

Did you Know:

  • Bobolinks are migratory birds with a 20,000 km round-trip migration route
  • 10% of the bobolink population breeds in Ontario, therefore this is an important jurisdiction for this species
  • Bobolinks nest on the ground in grassland habitats (e.g., fields and pastures)
  • They usually lay 5 eggs per nest
  • They are territorial during the breeding season
  • There is often more than 1 female nesting in a territory
  • In Ontario, nests are active from about mid-May to mid-July
  • 30 – 50% of nests fail in undisturbed fields
  • Fledglings walk out of the nest (they don’t fly) so are more vulnerable

Between 1968 and 2008, there has been a decline in the bobolink population of 88% across Canada (Government of Canada. COSEWIC assessment and status report on the Bobolink, Dolichonyx oryzivorus, in Canada. April 3, 2013. Ottawa, ON.) Habitat loss and a decrease in habitat quality are thought to be two of the main factors contributing to the bobolink population decline (i.e., decrease in hay and pasture areas in Ontario and; changes in agricultural practices that have decreased habitat quality for the birds).  Agricultural grasslands are extremely important to the bobolink species.  Campomizzi and Lebrun-Southcott are investigating possible conservation practices that farmers can implement to help support bobolink conservation.

Their research included looking at comparing breeding success between grazed and ungrazed paddocks, breeding success and stocking rates (the number of animals on a pasture for a specified time), and the impact of light spring grazing on bobolink breeding success.  It appears that the impact of cattle during the nesting season does affect bobolink fledgling numbers (54% fledged in ungrazed paddocks versus 16% in grazed paddocks).   Paddocks not grazed during the breeding season can provide good nesting habitat.  Bobolinks can breed successfully in lightly grazed paddocks and lightly grazed paddocks can provide good nesting habitat for bobolinks.  For the research study, light grazing was based on a stocking rate less than 40 (e.g., 35 cattle for 2 days in a 2-hectare paddock).  Light spring grazing can support successful breeding (4 paddocks were studied that included 12 territories and 18 nests).  With grazing beginning in late May, 67% of the territories fledged young. Half of the nests were initiated before or during light grazing; half were initiated after. There was no subsequent grazing from early June to early July, the peak nesting period. The timing of grazing and lower stocking rates in bobolink nesting territories appears to be critical for breeding success.

Research studies on bobolink will continue at Bird Ecology and Conservation Ontario (BECO).  The researchers hope to gather more data and provide more information to Ontario farmers and the public about conservation strategies for grassland birds, like the bobolink.  It’s imperative that we all work together to help protect these declining grassland birds and their habitats.

For further information on the work that Bird Ecology and Conservation Ontario (BECO) is doing, please go to

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