By Dr. Becker
More than 650 species of birds call North America their home during the summer (breeding) months. The majority of them are migratory, which means they typically head south to spend their winters in warmer locations.
The cold temperatures alone may not spur all the birds to travel south (hummingbirds, for instance, can tolerate freezing temperatures if they have a steady food source). However, a lack of food, which is common in the winter, will.1
In the world of migratory birds, there are short-distance migrants that travel simply from higher to lower elevations. Medium-distance migrants may travel across several states. Then there are the long-distance migrants – the birds that that spend their summers in the US and Canada, then travel to Mexico or even farther south for the winter.
Some of these trips involve journeys over the open ocean, requiring non-stop flight that would appear to be a virtually impossible feat, especially for a small songbird. The blackpoll warbler, which weighs less than half an ounce, is one such traveler.
Blackpoll Warbler Breaks Record for Longest Non-Stop Overwater Flight
There has been speculation that the tiny blackpoll warbler was making an incredible migratory journey. Canadian radar showed the birds heading south and very few were sighted in the US in the fall. The birds were also known to land on ships in the Atlantic.
To find out whether the speculation was true, researchers attached tiny tracking devices to the backs of the birds to follow their travels. It turns out the birds leave Nova Scotia and Vermont in the fall, then fly over the Atlantic Ocean to the Greater Antilles or the northeastern coast of South America for the winter.
This requires them to fly for up to three days without stops, over a distance of more than 1,700 miles. This breaks the record for the longest non-stop overwater flight by a bird when body mass is factored in.2 In preparation for the journey, the birds eat extra food to gain additional weight. Lead author William DeLuca, a research fellow at the University of Massachusetts, Amherst, told Discovery News:3
“It does fatten up, by almost doubling body weight and absorbing many of its digestive organs… It turns into a lean, mean flying machine, just wings, fuel, and a small orientation computer."
Other birds are also known to be impressive long-distance flyers. The northern wheatear, for instance, flies even farther over the Atlantic Ocean than the blackpoll warbler, although it’s more than twice as large. Ruby-throated hummingbirds also fly non-stop over water – the Gulf of Mexico – travelling at least 528 miles.4
Impressive Physical and Navigational Feat
The incredible overwater journey is not just a feat of physical intensity but also one of navigation. Chris Rimmer, a study co-author and Vermont Center for Ecostudies ornithologist, told the Washington Post:5
“It sort of defies the imagination on a number of levels… One is just the energy, the sheer energy and physiology required to propel a bird that many miles, an average of about 1,600 miles. But it's also a navigational feat, an orientation miracle in a way that the birds can strike out from land and head out over the water and reach their destination two or three days later."
How the birds navigate is still a mystery, but there are some theories. It’s thought that birds have an innate ability to know which direction and how far to travel during migration. Even birds that have been flown to different locations have returned to their nesting homes within a matter of weeks.
In one particularly poignant, albeit ethically questionable, experiment involving homing pigeons, the birds exhibited “almost unbelievable navigation skills.” As reported by the Cornell Lab of Ornithology:6
“German scientist Hans Wallraff transported homing pigeons to a very distant location. To ensure that the birds did not receive any external navigational information, they were transferred under stringent conditions. The pigeons were transported in closed, airtight cylinders and provided bottled air. Light was turned on and off at random times and loud white noise was played.
The cylinders were enclosed in magnetic coils that provided a changing magnetic field. Finally, the cylinders were mounted on a tilting turntable connected to a computer that varied both the rotation and tilt of the cylinders. After release at the distant and completely unknown area, the birds were able to fly home to their roost, apparently without trouble (other than an initial case of nausea).”
How Do the Birds Know Where They’re Going?
As for how the birds know where they’re going, a number of theories have been proposed, including:7
- Scent: Birds may use a map of odors that provides some directional information.
- Magnetic fields: Birds may be able to detect tiny changes in the earth’s magnetic field, which becomes stronger as you travel away from the equator.
- Sun compass: Birds may have a “sun compass” that’s tied to their circadian rhythm. They may use the sun’s azimuth direction (the compass direction at which a vertical line from the sun intersects with the horizon) as a means of navigation.
- Star compass: Many birds migrate at night, and it’s thought they may use stars for navigation. Specifically, some birds may learn a north-south orientation from viewing a rotational star pattern in the night sky. Interestingly, many nighttime migrants are also thought to start their journeys at sunset so they can use polarized light patterns for additional flight directions.
- Landforms: Birds may also recognize and follow natural landforms including mountain ranges, rivers, and lakes during their flights.
It’s likely that birds use a variety of these techniques, as well as others that are yet to be discovered, during their impressive migratory feats. It’s one of the factors that makes birds so fascinating, although they’re not the only species to migrate incredible distances.
Monarch butterflies, for instance, may migrate up to 3,000 miles, while a gray whale holds the record for the world’s longest migration – logging in 13,988 miles in 172 days. What makes the blackpoll warbler so unique, however, is its size – and the fact that it can travel so far regardless. Rimmer continued in the Washington Post:8
“If you can account for the size of this bird and the distance it goes… it's arguably more remarkable, maybe the most remarkable flight of its kind.”