by Jessé Roy-Drainville
Whether by day or night, birds swear by the wind for their long journeys. During migration, if the wind is in their favor, the birds will take flight, provided it blows in the right direction. On the contrary, if the wind is unfavorable, they will take the opportunity to rest and feed, waiting for the next favorable gust.
Dancing with the wind
In the Northern Hemisphere, in spring, it is typically the wind from the south that drives the majority of bird migrations, while in autumn, it’s a north wind. Although this might seem obvious, the situation is a bit more complex in Quebec: winds rarely blow strongly in these two directions.
Due to our latitudinal position and the Coriolis effect, west winds dominate in the province and surrounding regions. Thus, birds generally migrate with south-west and north-west winds.
The Tadoussac dunes, an exceptional site
A great place to observe the effect of winds on bird migration is the Tadoussac Bird Observatory. Autumn visual surveys at the Tadoussac dunes began in 1996, and more than 25 years of data have been collected on bird migration since then. From the end of August to late November, a seasoned ornithologist records precise details about wind strength and direction, as well as the number of individuals of each species observed in migration, every hour of observation.
The results are more than conclusive: a wind coming from the northwest quadrant (270 to 360 degrees) is optimal for bird migration observation. In fact, more than 70% of raptors are observed under these conditions each year.
The importance of monitoring wind conditions
Wind, therefore, proves to be the best indicator of migratory bird arrivals. It is essential to monitor wind conditions – its strength and direction – before heading out on a birdwatching hike during migration. This is especially true for birds that migrate mainly at night (the majority of insectivorous passerines, sparrows, owls, shorebirds, etc.) as well as for those that migrate during the day (diurnal raptors, finches, blackbirds, crows, woodpeckers, pipits, larks, etc.).
One application that can be very useful is called Windy. Available free of charge and regularly updated, it is fast becoming an essential tool.
Arrival of new species
If your ornithological interest is more focused on observing passerines, watch for the right winds during the night (from the southwest in spring and northwest in autumn), and bring out your binoculars at dawn the next morning. You may then witness an arrival of new, more northern species in your region or even early morning migratory movements, known as the “morning flight.”
These movements can be particularly impressive in Tadoussac at the end of May, when hundreds of thousands of birds have already been observed in a single day.
Observation sites to discover
If you prefer to observe large numbers of raptors or finches, monitor the same favorable winds, but ones that remain constant throughout the morning and extend ideally into the afternoon. Areas near large bodies of water, like the St. Lawrence Estuary, or near big cities, like the suburbs of Quebec City, are excellent places to observe real-time migration since birds are reluctant to cross these obstacles. If the winds push birds toward these large barriers, it becomes the perfect recipe for witnessing exceptional migratory phenomena.
The Tadoussac dunes, among others, meet these criteria, as do Hawk Ridge in Duluth, Minnesota, Cape May in New Jersey, and Veracruz River of Raptors in Mexico.
Birds that don't do as everyone else does
However, some bird species create their own rules when it comes to wind. It is often observed that certain species of gulls actually prefer headwinds for migration. For example, on days with strong south or southwest winds in the fall at the Tadoussac dunes, there are often very few or no raptors or passerines migrating.
However, gulls will still be present, and some days can see more than 2,000 gulls migrating, with notable numbers of Lesser black-backed Gulls (a species once rare in North-America) in September. This may seem counterintuitive, but there are reasons that could explain this phenomenon.
A question of structure
The structure of a gull’s wing is key: the headwind flows under the wing and pushes the back of the wing upwards, providing lift and propelling the bird forward. It is actually from these birds that the wing structures of modern airplanes were inspired. The shape of the wings, therefore, influences how the wind helps birds travel.
For example, the broad wings of Red-tailed Hawks allow updrafts to carry them high, and the long, streamlined wings of Blackpoll Warblers, shorebirds, or terns allow them to cover vast distances over several days, cutting through the wind even if it’s head-on.
Understanding bird migration is not an easy task. It requires combining solid knowledge of meteorology and geography, flight physiology, and the phenology of migration to better understand and predict bird movements. But even then, we are regularly surprised by bird movements. Witnessing a massive migration is such a striking and exceptional experience that it is worth taking the time to grasp its causes.
You can contribute to our monitoring efforts to better understand these movements and help protect the birds by supporting us here.