Migratory Birds

The Arctic tern, holder of the long-distance migration record for birds—50,000 miles each year.

One of the most fascinating times for birds is their annual migration, now underway. North America has more than 1000 bird species. Not all birds migrate, but about 75% of North American birds do. Here’s Cornell University's online BirdCast map that shows what’s happening, continually updated.

From the night of October 6, when BirdCast first recorded more than one billion birds in flight!

Bird migrations started some 40 million years ago, heavily influenced by the earth’s many glacial cycles. And although humans have been observing and writing about bird migration for thousands of years—it was discussed, for example, by Aristotle and in the Book of Job—it’s only within the last few years through impressive (and often quite technical) scientific advances that we getting a much better sense of what birds do and how they are able to do it. A few examples:

—Major improvements in technology (including using nanotags and a new antenna on the International Space Station) allow avian ecologists to track in real time the location of a migrating bird across the globe to within 30 feet, instead of 125 miles from the previous generation of tracking tags—helping us determine precisely where migratory birds face their greatest threats.

—Because most bird migration takes place at night, Cornell’s BirdCast uses AI technology to predict flight paths and alert communities when to turn down their night lights to reduce bird collisions with buildings and to minimize the disorienting effect of light pollution. States from Connecticut to Colorado plus many cities participate in these Lights Out campaigns.

—The ability of migrating birds to stay aloft non-stop for days at a time (the record is the bar-tailed godwit’s 8-9 day flight from Alaska to New Zealand) is now understood to be facilitated by “unihemispheric sleep” that allows them to put alternating halves of their brains to sleep for very short periods of time while using the other half to fly. (It’s the same principle that allows manatees and dolphins underwater to still surface regularly to breathe air while they are “sleeping.”)

—Physiological studies show that every year the bodies of migratory birds naturally go through several major adaptations getting ready for the arduous flight, including greatly boosting their muscle mass and basically restructuring their internal organs—including sharply shrinking their digestive system to lighten the load and then regrowing it once they arrive at their destination.

—Some remarkable research over the last decade indicates that migrating birds’ pinpoint navigation system is based on one of the weirder properties of quantum physics called “quantum entanglement.” It’s a property that involves subatomic particle action-at-a-distance and it’s central to creating a “visual map” in the bird’s eye of the earth’s magnetic field. (For the intrepid, here’s one of the “simpler” explanations of how this works.)

We’re in the midst of what’s being called, for very good reason, the golden age of bird research. All of the advances—with more to come—are bringing increased attention to the remarkable abilities of birds and giving us a better sense of exactly what’s needed to help protect them on their truly incredible migratory journeys.

To help make this more concrete, here’s the fall migration flight of one gray-cheeked thrush, as recorded by geotracker. About six inches long and weighing less than an ounce (the weight of a pencil!), she started in Alaska’s Denali National Park in early September, flew across the Yukon and British Columbia arriving October 5 in Minnesota; October 15 resting in Kentucky; October 18 in Mississippi; October 25 in Panama after crossing the Gulf of Mexico and the Caribbean; arriving November 30 to her destination at Venezuela’s remote Serrania De La Neblina National Park, where she stayed 4 1/2 months before embarking on the long journey back north again!