Mapping Birds Across a Changing Landscape
By Elizabeth Porter, Ontario Programs Engagement Specialist
From Backyard Sightings to Big-Picture Science
A bird’s song tells us a story about the natural world around us—but only if we’re willing to listen before more voices disappear. Breeding bird atlases are doing exactly that, by documenting where birds live and how their populations are changing over time. Atlases are carried out across Canada, and the Third Ontario Breeding Bird Atlas (Atlas-3, 2021-2025) makes Ontario the first Canadian province to have completed three. Together with Atlas-1 (1981-1985) and Atlas-2 (2001-2005), we know more than ever before about where birds are and how they’re doing across Ontario.
This is thanks to the over 2,000 volunteers who came together to survey birds during Atlas-3, gathering over four million observations that tell the story of 294 bird species. This data is the evidence that will guide conservation for years to come, and is increasingly important as climate change alters the habitats that birds depend on.
While broad-scale data may mask regional differences, atlases help us to see what’s going on when we zoom in. This can reveal more detailed trends that help to identify vulnerable areas and target conservation where it’s most valuable. It’s not just about knowing if birds are declining, it’s about knowing where change is happening.
Birds of the Greenbelt
A variety of habitat types, that support a diversity of birds, are found throughout the Greenbelt. During Atlas-3 an impressive 285 species were recorded across the 192 atlas squares that cover the Greenbelt (Fig 1)—that’s 97% of the species documented across all of Ontario! Lace up your hiking boots and grab your binoculars, and let’s get to know some of the birds that call these habitats home!
Through the Grass
Stepping into an open meadow, the hum of insects fills the air and a clear, slurred whistle drifts across the grass. It’s not long before the singer reveals himself, an Eastern Meadowlark perched on a fence post, surveying the landscape. Listed as Threatened, this species is found in 95% of Greenbelt atlas squares. But native grasslands are the most endangered habitats in Canada, and as they continue to decline, so do the species that rely on them. Atlas-3 data show a 26% decrease in this species’ abundance across Ontario in the past 20 years (Fig 2), and grassland birds as a whole have declined by 67% in Canada since 1970 (The State of Canada’s Birds). Protecting grasslands isn’t just about preserving open space; it’s about safeguarding the habitats that provide food, shelter, and nesting sites for birds like the Eastern Meadowlark.
Into the Forest
Leaving the open field behind, scattered shrubs give way to towering trees and the sounds begin to change. Pausing to listen, the ‘pee-ah-wee’ song of the aptly named Eastern Wood-Pewee rings through the forest. This species is recorded in 99% of the Greenbelt atlas squares, and between Atlas-2 and Atlas-3 there was a 29% increase in abundance in Ontario. The species’ range may be expanding in some locations along its northern edge (Fig 3), likely due to habitat adaptability, but it’s not all good news. The Eastern Wood-Pewee is a species of Special Concern, and as an aerial insectivore is part of a group that has experienced a 43% population decline since 1970 (The State of Canada’s Birds). Perched on an exposed branch, the pewee waits for insects to fly past before darting out to catch them, the interaction a reminder that it isn’t just the trees that are important, but the health of the entire forest ecosystem.
Among the Trees
Deeper in the forest, the trees are taller and the canopy closes overhead, but a flash of brilliant red through the leaves provides a glimpse of a Scarlet Tanager. On the breeding grounds, these birds have an affinity for interior forests and are sensitive to habitat fragmentation, which reduces nesting success. A long-distance migrant flying all the way from South America, Scarlet Tanager is found in 85% of Greenbelt atlas squares in Atlas-3. Throughout the province, the species has shown a varying pattern of gains and losses in different areas between the three atlases (Fig 4); however, between Atlas-2 and Atlas-3 there was a 15% overall increase in abundance across the province. When forests remain connected, forest interior species like the Scarlet Tanager can thrive.
On the Forest Floor
Looking down, the forest floor and understory are alive with movement, too. A distinct flute-like ‘ee-oh-lay’ gives away the location of a Wood Thrush rustling around in the leaf litter, foraging for insects and invertebrates. A species of Special Concern, Wood Thrushes rely on mature forests with well-developed understories for nesting and food. Population decline has been severe throughout southern and central Ontario, with a 26% decrease in abundance across the province since Atlas-2 (Fig 5). Canada-wide, this species has declined by a staggering 77% since 1970 (The State of Canada’s Birds). Wood Thrushes are a reminder that every layer of the forest, from the soil to the treetops, plays an important role.
Life Finds a Way
Walking through the forest, it’s hard not to notice standing dead and dying trees riddled with holes of varying shape and size. Loud drumming interrupts the morning chorus, and the large, red-crested head of a Pileated Woodpecker pokes out from behind a tree. Recorded in 90% of the Greenbelt atlas squares during the breeding season, this species is a year-round resident of Ontario forests and has seen a 38% increase in abundance in Ontario, with expansion along the southern and northern edges of its range in southern Ontario (Fig 6). As the largest living woodpecker in North America, Pileated Woodpeckers create spacious nesting cavities in large-diameter trees. Because they rarely reuse these cavities in subsequent years, they provide ready-made homes for other birds and mammals. Not every important tree in the forest is alive, and these holes are evidence that even in death the forest provides.
Where Forest Meets Water
As the trees become smaller again, a clearing comes into view, and a rusty coloured hawk soars overhead. The Red-shouldered Hawk, a less-common breeder in Ontario, gives itself away with a frequently repeated ‘kee-aah’ call announcing its breeding territory. Found in 28% of Greenbelt atlas squares, this hawk thrives in mature forests near water. Atlas-3 data suggest the Red-shouldered Hawk is experiencing losses at the northern and southern edges of its range in southern Ontario, and gains on the eastern edge (Fig 7). Although this hawk’s population has fluctuated since 1970, it is currently thought to be stable in Canada (The State of Canada’s Birds). Maintaining and expanding continuous forest corridors, wetlands, and intact ecosystems will help ensure its continued success.
In the Marsh
Leaving the shade of the trees behind, the forest floor gives way to soft, saturated soil at the edge of a cattail marsh. Several minutes pass before a Least Bittern appears, in quiet pursuit of a frog. This bird is classified as Threatened and is difficult to monitor due to its secretive nature. Atlas-3 introduced special surveys for marsh birds like the Least Bittern that are more often heard than seen, with 11 of these surveys completed in the Greenbelt. The patchwork of gains and losses in atlas squares in southern Ontario (Fig 8) likely reflects habitat destruction, sensitivity to human disturbance, and possibly the increase in monitoring effort between atlas periods. Marsh birds have very specific habitat requirements, and as such, their presence is often indicative of a high-quality wetland.
Resting Stops for Tired Travelers
Our journey through the connected mosaic of grasslands, forests, and wetlands of the Greenbelt makes it clear: to protect the diversity of birds and other wildlife we share this space with, we must steward not just individual habitats, but the connections between them. In addition to supporting local breedings, healthy habitats play a key role for species migrating to breeding grounds further north. For example, the Urban River Valleys of the Greenbelt offer safe stopover spots where birds can rest and refuel during their long journeys. Understanding which birds use these spaces, and how, provides us with valuable information to guide research, conservation and management planning, and the development of policies and recovery strategies for species at risk.
Healthy, connected habitats are key for species success, and every piece matters. You can help by creating safe spaces and reducing the risks birds face as they travel from one area to another. You can plant native plants in your yard or in planters on your balcony, support community gardens and green spaces, make windows safer for birds, keep cats from roaming outside, avoid pesticides, or contribute to bird conservation by volunteering for another Birds Canada program! Together, we can take action to ensure the voices of birds are loud and clear for generations to come.
About the Atlas
Atlas-3 is a collaborative effort between Birds Canada, Canadian Wildlife Service (Environment and Climate Change Canada), Ministry of Natural Resources – Government of Ontario, Ontario Field Ornithologists, and Ontario Nature. We are grateful to the Greenbelt Foundation for the generous support of this work. It is because of these strong collaborations and the incredible contributions of thousands of volunteers that we are able to share the important information and strong science that will be used for evidence-informed bird conservation in the face of significant habitat loss and species decline. Print and digital publications of Atlas-3 will be available in Fall 2027. You can directly support bird conservation by donating to the Ontario Breeding Bird Atlas through this secure link.