Science in the Forest: Searching for Ontario’s Rarest Birds

By Samreen Munim and Brendan Boyd, Ontario Forest Birds Program

Every year, as the snow melts and the cold winds of winter slowly let up, the first signs of spring emerge and we head back into the forests of Southern Ontario. Here we remain for the next few months, dedicating the better part of our days to finding some of the rarest and most at-risk forest birds in Canada: Acadian Flycatcher, Cerulean Warbler, Louisiana Waterthrush, Prothonotary Warbler, and Red-headed Woodpecker.

Southwestern Ontario, or the Carolinian region of Canada, was once largely forested. Extensive clearing for agriculture during the 19th century has left only a small, highly fragmented remnant of the once large mature forests. The small patches that remain are often not managed for conservation, resulting in little suitable breeding habitat for these five species.

The Forest Birds at Risk Program aims to monitor, study, and work with land managers to protect habitat, guide stewardship actions, and mitigate any threats that we might find including invasive species and tree diseases. We also complete targeted research projects to improve our understanding of these species, their habitat needs, and the most effective conservation strategies for them.

The work we do would not be possible without strong and collaborative partnerships, months of preparation and communication, and the hard work of our staff. Here is a small glimpse of what that entails throughout the year!

Photos L to R: Acadian Flycatcher by Gabriel Evans-Cook, Cerulean Warbler by Trisha Snider, Louisiana Waterthrush by Sean Jenniskens, Prothonotary Warbler and Red-headed Woodpecker by Trisha Snider

January to March: Planning for the Field Season

All five of our target species abandon Ontario for the cold winter months (except some hardy Red-headed Woodpeckers that stick around). This gives us much-needed time to prepare for their return so we can hit the ground running in April. Our vast checklist comes out and we start ticking the boxes: hiring summer staff, meeting with partners, updating our equipment inventory and safety protocols, creating site lists, mapping routes, presenting to stakeholders, submitting permit requests for land access, and reaching out to private land managers to organize surveys.

Giving a presentation at a conference for woodlot managers. Photo: Kevin Predon

Samreen works on a difficult analysis with help from Dr. Danielle Ethier, Birds Canada’s Senior Scientist, at Birds Canada Headquarters. Photo: Josh Sayers

April to May: Louisiana Waterthrush Monitoring

Most of our target species return to their breeding grounds in May, but the earlier arrival of Louisiana Waterthrush in April marks the beginning of our field season. This early arrival means they are easily overlooked in other breeding bird surveys that begin in late May. Population estimates for Louisiana Waterthrush are uncertain in Canada, so these dedicated efforts are extra important.

When we locate waterthrushes, we look for breeding evidence, assess the habitat they are using, and communicate any threats found with land managers. For example, our work with a local partner ensured that buffers are placed around breeding streams to minimize potential negative effects from nearby harvest operations. Working with our local partners is crucial for the successful conservation of species at risk, and we’re grateful to work with so many passionate and engaged people!

One of our summer staff listens for Louisiana Waterthrush at a breeding site. We look for the nests by patiently watching for the female coming and going while incubating eggs or later tracking the parents as they carry insect food to their young. Eventually, we get to see the clumsy fledglings relentlessly begging for food as they chase their parents up and down the streams! Photo: Samreen Munim

Louisiana Waterthrush. Photos L to R: Jack Belleghem, Julia Marshall, Jack Belleghem

June to August: General Surveys and Continued Monitoring

Most birds in southern Ontario start to breed by the end of May, which is when we begin our more general bird surveys. We use a standardized method called ‘point counts’ to efficiently cover a lot of ground. These point count surveys involve visiting predetermined locations that are evenly spaced across the entire forest, then completing 10-minute counts of all the birds heard and seen at each location. We also record all the birds detected between the different point count locations. By revisiting the same locations across years we can more readily compare species numbers and abundance over time. We also specifically look for nests and monitor breeding activity for our target species.

Some of our sites have trails, but more often than not, we aren’t so lucky. This means long days of climbing up and down steep and muddy ravines, splashing through swamps, and being poked by spiky thickets of rose and raspberry. By day’s end, we’re caked in dirt and sweat, covered in mosquito bites (and probably some hidden ticks), and occasionally sloshing in a flooded boot or two – but we love it!

These are the days we dream about all winter from behind our desks. The conditions can be challenging, but we stumble across caves and waterfalls, find carpets of colourful wildflowers, become immersed in birdsong as it fills the canopies, and spend serene moments observing diverse wildlife – rare reptiles and amphibians, charismatic mammals, and an endless variety of incredible insects like moths, butterflies, dragonflies, beetles…the list never ends! All of it unfolds beneath a lush canopy of oaks, maples, beech, hickories, and more, swaying gently in the warm summer breeze. These moments far outweigh the challenges for us.

Travelling through the great Carolinian forests of southern Ontario, which include some of the best remaining protected areas for these at-risk birds, is a privilege we don’t take lightly. We stick to trails where they exist, avoid trampling vegetation, and clean our gear regularly to limit the spread of invasive species.

Invasive species are a serious concern for many of our target birds, so we keep an eye out for them on every survey. When we find evidence of one or more, we share the location with land managers and recommend best management practices to help mitigate impacts where possible. For example, in 2025, we found a new infestation of Hemlock Woolly Adelgid at a site where there was a singing Acadian Flycatcher (we chat about this on The Warblers Podcast if you’d like to dive deeper!)

We also run a variety of projects each year focused on our target species. Currently, we work with several experts to support and monitor Prothonotary Warblers through a nest box program (huge thanks to Dean Ware, Don Wills, and Lucas Foerster!), which has shown that Prothonotary Warblers are doing better than they have in decades. We also monitor the Cerulean Warbler population in eastern Ontario with Dan Derbyshire and after 10 years know that the population has remained stable. We have several more projects on the horizon that will help us continue to fill key knowledge gaps, work with our strong network of partners, and help advance recovery for our target species.

Our field surveys involve a lot of bushwhacking! Photo: Samreen Munim.

Hemlock woolly adelgid, the white balls clustered on the central twig, are an invasive species that kills eastern hemlock trees, which Acadian Flycatchers and Louisiana Waterthrush rely on. Photo: Brendan Boyd.

We stick to trails where they exist. Here, we walk through Backus Woods, one of the largest remaining forest complexes in southern Ontario. Photo: Samreen Munim

Binoculars come in handy for more than just birds. Here, one of our summer staff scans treetops for invasive species. Photo: Samreen Munim.

September to December: Data, Grants, and Writing

By September, most of the birds we focus on have departed for their non-breeding grounds in Central America, South America, and the US. We sadly put away our boots and (not so sadly) our bug spray, but the work is not over! We brush the dust off our desks and start to tackle all the data we collected over the spring and summer – sharing bird lists and invasive species with each land manager and partner, along with resources and advice on best management practices and stewardship activities.

On top of all that, we are also busy analyzing data from past seasons, catching up on the latest research, providing updates to funders and supporters, writing grant applications and reports on our findings. For example, in 2025, we completed our 10th year of monitoring Canada’s largest population of Cerulean Warblers (representing nearly the entire national population), allowing us to see how the population is doing (spoiler alert: it seems stable!).

None of this work would be possible without strong relationships with our partners! We’re grateful to all the funders that have supported our work over the years and still support us today. We’re also indebted to everyone who has contributed, whether by allowing us to survey on their properties, by working with us to mitigate threats, by inviting us to share information on forest birds, or by directly helping us collect the data – despite the biting bugs, scorching heat, and flooded boots!

See you in the forest!