Turkey Vultures on Vancouver Island Are Crossing Later

Each autumn, turkey vultures gather at the southern end of Vancouver Island, a large island off Canada’s Pacific coast, and wait.

For days, and occasionally longer, they wheel overhead, monitoring the water and waiting for favourable winds before attempting a passage across the cold open sea.

Since 1999, a small research team has counted these gatherings.

After 25 years of observations, the records revealed something nobody had set out to find.

Counting the kettles

Turkey vultures are large, dark-coloured scavengers, with a wingspan of about 1.8 metres and bare red heads.

Every autumn, many of them travel down the length of Vancouver Island, off Canada’s Pacific coast, until they reach its southernmost point.

At this gathering place, they create formations known to birdwatchers as kettles: loose groups spiralling upwards in columns of warm rising air. This allows them to gain height without effort before gliding onwards.

The term comes from a kettle-shaped hollow at an early hawk-watching location.

For 25 years, volunteers at Rocky Point Bird Observatory (RPBO), a monitoring site near Victoria, logged the number of vultures gathering before the sea crossing.

Dr Daniel Dönnecke, a long-standing volunteer at the observatory, and Dr Don Kramer examined whether these kettles had changed from 1999 to 2023.

The water barrier facing turkey vultures

The obstacle is the Strait of Juan de Fuca, a stretch of cold sea roughly 18 km wide between the island and Washington State.

Because cold water suppresses the rising air currents on which these birds rely, crossing by flapping is difficult and hazardous.

Instead, they wait. Hundreds of vultures accumulate at the island’s tip, using local air currents and waiting for a day with light, favourable winds before making the crossing together.

Some breed throughout southern British Columbia and Vancouver Island before travelling vast distances south for winter; a few reach Venezuela.

Others do not migrate and remain in place, making annual population estimates for the species more difficult.

What 25 years of counts reveal

The 25-year pattern was difficult to overlook.

The highest single-day total each year rose by almost 300% between 1999 and 2023, consistent with long-term studies showing that these vultures have expanded northwards across the continent.

Their migration also shifted later. Compared with the beginning of the study, the vultures started crossing around four days later in the season, representing a modest but persistent change over a quarter of a century.

“We were surprised to see how strong and clear the pattern was,” said Dönnecke.

The western trend is especially notable because recent information had previously been scarce.

Eastern populations have been monitored for years, whereas the western population had remained largely uncounted until this research, leaving conservationists reliant on an estimate that was decades old.

A potential climate connection

The reasons for both trends are much less clear.

The researchers believe climate change could be involved: warmer autumns may enable birds to remain on their breeding grounds for longer, while milder conditions could allow more vultures to survive and reproduce.

However, they are cautious not to claim too much. The counts show an increase in birds and a later departure, but they do not establish the cause of either change.

Research on soaring birds in Europe has associated hotter autumns with later seasonal departures. The Vancouver Island findings are consistent with that pattern.

There is also a more straightforward explanation within the figures. A larger number of vultures crossing each year does not necessarily indicate a rapidly growing population, because the count is made at a single bottleneck where birds concentrate closely together.

It is the broader surveys that lend support to the apparent trend.

A method suitable for other migration sites

For bird researchers, the study presents a less costly monitoring approach. At hawk-watch locations, observers count individual birds as they pass, requiring long hours and consistent staffing.

By contrast, counting entire kettles can identify a trend with considerably less time and staffing.

Soaring birds encounter bottlenecks wherever large expanses of water interrupt their route, including along coastlines and at narrow land bridges.

The same kettle-counting approach could be used at such sites, allowing teams to monitor migrating birds of prey without the staffing demands of a full hawk watch.

Dönnecke and Kramer hope the research encourages counting stations to compare their data on changing migration timing among species.

A single location provides only one account. A network of sites could reveal whether these vultures are unusual or part of a much broader shift.

Why vultures matter

Understanding the status of these scavengers matters because they perform a task that few other animals undertake.

By quickly consuming carcasses, vultures prevent dead animals from becoming breeding grounds for bacteria that can harm wildlife, livestock and people.

Their stomach acid neutralises germs that would otherwise thrive in decaying bodies, making their loss potentially dangerous.

One study of carcass scavenging found that, when vultures vanish, slower scavengers move in and the risk of disease increases. Detecting a decline early gives wildlife managers an opportunity to respond.

What was once uncertain is now documented. In this part of the continent, western turkey vultures appear to have become much more numerous over 25 years and now leave several days later than they once did.

Recorded using a method simple enough to apply in almost any location, the findings create an opportunity to monitor birds at crossings that have never previously been studied.

A widespread bird, carefully observed, can reveal how the weather is changing across an entire region.