Canadian Wildfire Smoke Makes New York Birds Harder to Spot

Smoke from Canadian wildfires has become an increasingly familiar issue in New York, prompting air-quality alerts and driving more people to accident and emergency departments.

Researchers have now identified another unexpected consequence. As wildfire smoke arrives, dozens of bird species become markedly more difficult to see.

A new study, led by researchers at the University at Buffalo (UB), found that 40 bird species were less likely to be recorded as concentrations of fine particulate matter, or PM2.5, increased across the state.

Many of these were migratory forest songbirds, which birdwatchers generally identify through their songs or movements among the trees.

That does not automatically mean the birds had vanished. Instead, they may have altered their behaviour – a finding that raises significant questions about whether wildfire smoke can distort the data used by scientists to monitor wildlife populations.

Wildfire smoke could distort bird counts

“Our results show a link between wildfire smoke and the probability of observing particular bird species,” said corresponding author Festus Adegbola, a PhD candidate in UB’s Department of Geography.

“Wildfire smoke is often underexplored when monitoring biodiversity. Failing to account for air quality may bias models of species distributions and abundance.”

Much of today’s biodiversity monitoring depends on models developed using public wildlife-sighting records.

If smoke changes the number of birds that observers notice, without that effect being considered, these models may provide a misleading account of where species occur or whether their populations are rising or falling.

Tracking birds through smoky conditions

The researchers first examined PM2.5 concentrations across New York during the 2021 to 2023 breeding seasons.

The conditions of 2023 stood apart, when smoke from Canada’s record-breaking wildfires blanketed New York and damaged air quality throughout June and July.

PM2.5 measurements repeatedly exceeded World Health Organization (WHO) guidance, reaching eight times the recommended limit at one stage.

The team then matched pollution records against nearly 99,000 birdwatching checklists from Cornell University’s eBird database.

Run by the Cornell Lab of Ornithology, the citizen-science initiative has grown into one of the largest bird-observation datasets in the world.

Checklists gathered statewide

The checklists were submitted by birdwatchers with widely varying levels of experience. Researchers applied rigorous data filters and statistical techniques to allow for those differences.

This method helped the team establish that the pattern was genuine, rather than an artefact of inconsistent reporting.

The study included 84 bird species. Researchers assessed them using approximately 99,000 checklists submitted throughout the state during three breeding seasons.

Forest songbirds were most affected

Almost half of the species examined were reported less frequently as PM2.5 concentrations increased.

Many were migratory forest songbirds, including warblers, thrushes and vireos. Birdwatchers commonly find these species by hearing their calls or noticing movement in the canopy.

“It’s possible that smoky conditions changed the birds’ behavior – singing and moving less, spending more time in dense forest canopy – and therefore made them harder to detect,” said Adegbola.

On paper, a bird that has fallen silent and retreated further into cover is indistinguishable from one that has genuinely left the area or declined in abundance.

Yet those possibilities represent two entirely different situations concealed by the same reduction in sightings.

Some birds were recorded more often

The response was not uniform across all species. Fifteen species were actually observed more frequently as smoke concentrations rose, while 29 others showed no meaningful change in either direction.

This group was weighted towards aerial insectivores and certain wetland birds, species that typically occupy more open habitats than the forest songbirds most strongly affected.

However, the increase in records does not necessarily indicate that smoke benefited these birds.

“These species often occupy more open environments than forest songbirds,” said co-author Adam Wilson, an associate professor of geography at UB and Adegbola’s adviser.

“It’s possible their increased sightings had more to do with where birdwatchers chose to observe during smoky conditions than how the birds themselves responded.”

In other words, birdwatchers may simply have sought out different locations during periods of smoke.

They may have favoured open fields or wetlands, where conditions seemed clearer, potentially increasing reports from those habitats regardless of what the birds were actually doing.

Birds absent from records may still be present

The key message is one of caution for those using citizen-science data to follow wildlife: a fall in bird sightings during smoky periods does not necessarily indicate that fewer birds are present.

It could instead mean the birds were less noticeable, either because their behaviour changed or because observers chose different places in which to look.

Making that distinction correctly is highly important for biodiversity monitoring. If a short-term reduction in detectability is mistaken for a real population decline, conservation resources could be directed in the wrong way.

Wildfire smoke requires closer scrutiny

As a warming climate is expected to make wildfires increasingly severe, the researchers regard the study as an important early stage in a far broader effort.

“Still, as climate change continues to intensify wildfires, it’s crucial we understand how birds will be affected by increased smoke pollution,” Wilson said.

“This study is hopefully a first step to better understanding how species respond to wildfire smoke exposure.”

As smoke-filled summers become increasingly frequent, understanding how they alter bird behaviour will be ever more important.

Researchers will also need to consider smoke’s impact on bird-monitoring work. This will give a more accurate view of how wildlife is truly coping in a changing climate.