Earth Protect Blog

While you sleep, millions of birds will migrate over Colorado

By John Meyer

The Denver Post

While you slept one night this week, more than 30 million migratory birds flew over Colorado, almost five times the number that were aloft the night before, at an average speed of 28 mph and an average altitude of 1,100 feet. And of those, more than half completely crossed the state en route to their winter habitat.

We know those things, and a whole lot more, because of a fascinating website operated by a consortium of ornithologists at Colorado State University, the Cornell Lab of Ornithology and the University of Massachusetts-Amherst.

It’s called BirdCast. It uses Doppler radar to detect birds in flight during migration seasons (fall and spring) the same way it tracks where it’s raining or snowing, except meteorologists filter out radar return from birds. Radar ornithologists filter out returns from weather.

One of BirdCast’s features is a time-lapse map of the U.S. showing migration that occurred the previous night with migration areas color-coded by intensity as well as the direction birds traveled. A line marking the edge of night moves east to west, showing the way migration explodes over Colorado after night falls. You can also type Colorado — or your county, even — into a feature called Migration Dashboard to get all sorts of data on what happened overhead while you slept.

Data feeds are available during fall migration, Aug. 1-Nov. 15, and spring migration, March 1-June 15.

Kyle Horton, an associate professor in CSU’s department of fish, wildlife, and conservation biology, supervises a 10-person team of undergrads, graduate students and post-doctoral fellows who work on BirdCast.

“We do it for a number of reasons,” Horton said. “A big one is advocating for the conservation of migratory birds and disseminating information to the public. Bird watching is one of the top hobbies in the U.S. When we tell people that there’s millions of

birds migrating, or that ‘Last night there were 300 million birds predicted to be flying across the U.S.,’ that really grabs their attention and their excitement, their wonder.”

This is an exciting time of year for bird watchers. Zach Hutchinson, community science coordinator for Audubon Rockies, said every migration season brings hope.

“It keeps things fresh and exciting and new,” Hutchinson said. “It doesn’t matter how many migrations you’ve been through, there’s always a chance you could see a new bird — even if I’m just sitting in the office where I have a feeder or two outside the window.”

BirdCast is a great tool for bird-watchers from veteran to novice. Its mission is part educational, part advocacy.

“Often it gets (the public) excited about making a change, like turning off lights, or getting up early to see what landed, what’s new in your backyard,” Horton said. “There is mystery wrapped up in bird migration. What’s going to show up? You don’t ultimately know that answer until you go out and explore a little bit. It’s exciting for us to engage with the public, with stakeholders, in that capacity.”

Ornithologists say light pollution is a significant threat to birds because it causes disorientation and collisions with buildings while upsetting birds’ internal clocks. The slogan for World Migratory Bird Day on Oct. 9 is “Dim the Lights for Birds at Night.”

“With light pollution, we have a quick and easy solution,” Horton said. “We could fix it tonight if you had enough collective will. That’s not true for all threats that birds are facing. If we talk about land conversion or climate change, if we change those things today, they might take decades to rectify. We know what the issue is with light pollution, and we know how to fix it — turn off lights, dim lights. That can be done very quickly.”

In addition to reporting raw numbers of nightly bird migration over a given state or county, BirdCast has lots of other fun info. It posts a daily line graph showing hourly numbers of birds in migration the night before. For example: the 30-million peak on Tuesday night occurred at 3 a.m. Wednesday. There are line graphs showing nightly numbers for the season since Aug. 1, flight direction, speed and altitude hourly through a given night, and more.

And, because some of those migrating songbirds might make a pit stop in your backyard, BirdCast lists birds likely to be migrating through Colorado. Each bird on the list is shown in a photo. If you click on the bird, you can see more photos along with some facts about that species and their travels.

Most birds migrate at night, Horton said, because of cooler temperatures, calmer winds and fewer threats from predators. Colorado is the destination for some, usually those that breed in Alaska and Canada before wintering here. Birds that spent their summers here will be heading to New Mexico, Mexico, even South America. One of them is the bobolink.

“It might breed in parts of Colorado but spends its winter in the southern reaches of South America,” Horton said. “They’re going thousands of kilometers. Some might fly over the Gulf of Mexico for a day straight, make landfall on the Yucatan Peninsula in Mexico, and venture into Colombia, Brazil and Chile.”

The reason birds migrate is not to escape cold temperatures.

“They can probably tolerate some cooler temperatures,” Horton said. “Mostly what they are tracking is food resources. Cooler temperatures often result in lower amounts of food for these birds, especially when they’re eating insects, like a bobolink would be.”

Jagers passing through Colorado are traveling from the Arctic Circle en route to South America.

“Which is just incredible,” Hutchinson said, “to have that connection with a place (the Arctic) that many folks might never get to see, but they’ll get to see a piece of it possibly passing through their local pond or lake.” John Meyer: 303-954-1616, This email address is being protected from spambots. You need JavaScript enabled to view it. or @johnmeyer