Every year, billions of birds from over 300 species migrate to Canada’s Boreal Forest to breed, and twice as many make the journey south to warmer wintering grounds.1 Some days at the Lesser Slave Lake Bird Observatory, we may see thousands of geese or songbirds flying overhead in the early morning hours, but this is just a sliver of migration. Most of it is actually happening as we sleep.
While running our nightly owl migration monitoring program, it is not unusual to hear geese or Sandhill Cranes passing overhead. Sometimes we can even pick out smaller songbirds like sparrows chipping as they go.
Above: Although most birds have already taken the red-eyed flight farther south, our White-throated Sparrows are on a lay-over and we’ve been recapturing them in relatively high numbers this week.
This might come as a surprise. Songbirds and waterfowl are not generally known to be nocturnal, and while it is true that you probably will not see an American Robin poking around for worms at midnight in your backyard, migrating at night provides several benefits. It is cooler, which means reduced water loss, with calmer winds and fewer predators like falcons and Sharp-shinned Hawks.
Mass nocturnal migration became apparent nearly a century ago with the advent of radar. Initially the idea was waved away, since the volume of birds required to produce an echo on radar seemed ludicrous.2 Now, with the Doppler weather radar system—the same system we use to check the rain forecast—we are able to see how birds move at night.
Birds will migrate between 500 and 5,000 meters up, becoming visible on Doppler radar where they intersect radar beams, often occurring in pulses when they take flight as a group.
The continental United States has an expansive weather radar network. With coast-to-coast coverage, the project BirdCast was born using data filtered from weather events. Using this extensive network, American researchers can predict the intensity of nocturnal migration up to three days in advance.3
Above: The BirdCast migration forecast for September 13th, 2024. Predicted high intensity areas are shown in yellow.
Birds are not the only non-weather movements visible on radar. Insects such as mayflies can occur in blooms, but since they follow the course of the wind due to their size, they are easier to differentiate from birds. Bats are more similar to birds on radar, but their blooms are caused by foraging flights during the summer months, compared to birds’ spring and fall migration activity.3
Unfortunately the Canadian weather radar network only covers the country’s most populated regions. This means the most remote parts of Canada do not have the same coverage as the United States’ weather network. This large blind spot also happens to cover most of the boreal forest, creating a gap in our knowledge of nocturnal migration in Northern Canada.
If you are interested in more information about nocturnal migration and the weather radar network, and to see the migration forecast for the U.S., visit BirdCast.info. For a chance to see low morning flights locally, a very early morning trip to the station is your best bet. Migration most mornings slows dramatically within three hours after sunrise.
By Bronwyn Robinson, LSLBO Assistant Bander
References
- North America’s Bird Nursery — Boreal Conservation. (n.d.). Boreal Conservation. Retrieved September 11, 2024, from https://www.
borealconservation.org/north- americas-bird-nursery - Bogard, P. (2021, season-01). A new golden age of observation is revealing the wonders of night migration. Audubon. Retrieved September 11, 2024, from https://www.audubon.org/
magazine/spring-2021/a-new- golden-age-observation- revealing-wonders - Eschliman, C., & Horton, K. (2024, June 15). A primer for using weather surveillance radar to study bird migration – BirdCast. BirdCast. Retrieved September 11, 2024, from https://birdcast.info/news/a-
primer-for-using-weather- surveillance-radar-to-study- bird-migration/
