Whether catching the streak of a hummingbird zoom by mid-summer or enjoying the majestic V-formation of geese crossing the hazy sky at dusk, bird migration is a delight for birdwatchers. After all, it gives us the chance to observe and enjoy different species that aren’t year-round residents in our neck of the woods.
The beauty of bird navigation is quite complex. If you’re one who can’t drive anywhere without clear step-by-step directions, you’ll be blown away by the way birds navigate. Birds use little more than their own senses and the Earth around them.
Why Is Navigation So Important?
For many migratory birds, proper navigation can mean the difference between life and death. An extended trip to another region is much more than a simple winter getaway. Weather and food are the main factors that cause birds to adopt seasonal migration. Nesting preferences often prompt migratory birds to settle near temperate areas in the spring, followed by an escape to warmer areas when winter approaches. Botched navigation can mean ending up in a region that is low on food sources. The area might also present harsh, unlivable, even deadly weather conditions—either too hot, too dry, or too cold.
See also: How Do Birds Survive Winter?
As most birdwatchers know, certain species typically follow the same flyway—or flight path—each year. Some migratory birds, like geese, swifts, and swallows, travel together as a flock. Others, like owls, hawks, and hummingbirds, are more likely to be spotted making a solo trip. But whether traveling alone or in a group, error-free navigation is absolutely vital to making a safe and successful journey.
So how do they do it? As it turns out, birds are capable of reading the Earth’s magnetic field in order to navigate their determined flyway.
See also: Does Feeding Birds Hinder Migration?
Decoding the Earth’s Magnetic Field
The surface of the Earth is blanketed in a magnetic field, thanks to electric currents generated from the planet’s continuous movement. While the Earth’s magnetic field is invisible to the human eye, it can be witnessed with a basic scientific tool: the compass. The Earth’s magnetic field is stronger at the two poles (North and South) and weaker at the Equator. That's why a compass—a properly functioning compass, that is—always points north.
Just as a compass uses magnetism to determine position and point north, birds are capable of ‘reading’ the Earth’s magnetic field to find their direction, too. The change in magnetism between the poles and the Equator is particularly helpful. It allows birds to gauge distance and direction when migrating north or south over long distances. In a way, a bird’s ability to detect the magnetic field is sort of like having a built-in GPS!
See also: Hummingbird Migration Patterns Explained
How Birds ‘Read’ Magnetism
So how are birds able to use the magnetic field as a map? We mere humans are condemned to fiddling with a compass, charting out points on an atlas, or scrambling to plug in a smart phone GPS that’s losing its charge. The answer lies in the eyes (and ears and beak).
Researchers recently figured out that a specific protein found in bird eyes, referred to as the Cry4 protein, is able to detect the Earth’s magnetic field. While the research was conducted with zebra finches, it’s believed that all birds have the Cry4 protein. That includes both migratory and resident birds. And though researchers aren’t quite sure what the magnetic field might look like to a bird, it’s pretty clear that birds are able to ‘see’ it or gauge it nonetheless. Furthermore, the Cry4 protein is present in the eyes at a steady level throughout the day and night. This means birds are able to stay in tune with their internal magnetic compass even after sunset.
In addition to the Cry4 protein, birds have a tiny amount of iron in the inner ear. This also contributes to their detection of the Earth’s magnetic field. And, certain nerves found in a bird’s beak may even be able to assess the precise angle of the magnetic field. That's helpful in providing additional data that the bird can use to determine position and location on the globe.
Talk about a high-tech GPS configuration! By ‘reading’ the magnetism of the Earth, birds are able to determine north and south, thus sticking to their projected flyway when heading out on a long trip.
Extra Navigational Tools
While assessing the Earth’s magnetic field is a pretty cool way to map out a journey, birds do rely on other skills when navigating cross-country. For example, birds can consult the position of the sun and stars to help identify location and stay on route.
And if you’re convinced that some of the seasonal guests at your backyard feeder always make a point to visit your yard each year, you may be right. Another way that birds are able to stick to their flyway is by seeing and smelling the surrounding terrain. Some researchers believe that birds can actually recognize landmarks along the way.
So it just may be the case that some of your favorite birds are looking forward to a relaxing pit stop in your yard during a long migration. That's good reason to keep that bird bath filled to the brim with fresh water and feeders stocked full of nutritious food. After all, you don’t want the birds to leave a bad review!