Cooler temperatures are setting in, and days are getting shorter. That means many bird species across North America are now flocking up and flying southbound where warmer weather and sunnier days await.
It’s an annual pilgrimage that is well documented and heavily studied by biologists and modern technology has revolutionized how scientists study the phenomena of avian migration. According to the Washington Post, weather radar systems have gotten so advanced that they can now help calculate how many birds are moving through an area.
A recent report from Birdcast.info concluded that as many as 430 million birds were cruising over the continental U.S. one night recently. During migration, most birds take to the sky around sunset and fly through the night before finding a place to rest around sunrise. Counting birds in the dark is a difficult task, but researchers have been using weather surveillance radar to refine the process of counting migrating birds for years now.
Birdcast helps interpret those radar patterns and turn them into easy-to-understand migration maps that display bird migrations across the country in real time. The analysis shows actual bird migrations detected by weather surveillance radar systems across the country. Areas with lighter colors represent the most intense bird migrations, while the arrows indicate which direction birds are flying. The green dots represent radar systems that help track migration, but it’s important to note that the radar systems are often obstructed in mountainous areas, so the maps often indicate that no birds are migrating through those areas when that is not necessarily the case.
Migration patterns tracked on a nightly basis can be layered over time to create a seasonal display of bird migrations like this animated map that depicts giant conglomerations of birds flying north in the spring and then back down south in fall.
“This is one of my favorite visuals, especially this time of year season transitions – migration patterns of birds varying with air temperature using community science data. Enjoy!”
Bird migrations are constantly in flux, so measuring them can be a challenge, but to help envision how migration numbers are calculated, envision a hypothetical pathway running down the east coast that measures about 1 mile wide and then envision another line running across that path. Now imagine about 80,000 birds flying across that intersection every hour, and that’s just for a one-mile stretch.
Then consider that similar rates of birds flying south are consistent from pretty much everywhere east of the Appalachian mountains and across the Great Plains and it becomes easier to conceptualize the unfathomably large number of birds in the air each night during migration.
Studying these migrations would be more challenging without the aid of doppler radar, which works by emitting a pulse of energy away from the radar system that ripples out into the air until it bounces off an object in the sky. Typically that object is a cloud of precipitation, and once the radar wave hits it, it is reflected back towards the radar, which picks up the echo. The process is refined enough that the radar systems can tell the difference between rain, hail, snow, or ice. The radar systems can also interpret the particles’ size and velocity, which helps meteorologists understand weather patterns and develop forecasts. It also helps scientists detect birds on the radar systems.
The process has been refined enough now that radar signatures from birds can be differentiated from radar systems from weather patterns.
Recently, a variety of weather-related factors caused the doppler radar systems that monitor the weather for Baltimore and Washington D.C. area to area to monitor conditions lower in the sky than usual, and the radar system picked up a large mass of objects scattered throughout the sky moving in a north/northeast to the south/southwest direction in a pattern that looked like storm clouds rolling across a weather map.
Additional radar coverage from Iowa also recently picked up a gigantic flight of birds taking off for their morning flight in such high numbers that it showed up on a live weather map as precipitation.
“Good morning to all the birds of central Iowa. We captured your take-off on our Doppler radar! There were so many of you; our radar tried to switch into precipitation mode!”
Bird experts recommend that people turn off outdoor lighting this time of year as the artificial light can negatively impact bird migrations by diluting natural light sources and other environmental beacons birds use to map out their annual migrations.
To help with citizen science initiatives focused on tracking migrations and other cool bird related initiatives, check out the eBird website and app.
For more information about how biologists track bird migrations beyond just using weather radar systems, check out this short film below.
“For thousands of years and countless generations, migratory birds have flown the same long-distance paths between their breeding and feeding grounds. Understanding the routes these birds take, called flyways, helps conservation efforts and gives scientists better knowledge of global changes, both natural and man-made. QUEST heads out to the Pacific Flyway with California biologists to track the rhythm of migration.”
