The migration of birds
By Ben Stalheim
As a kid, I would look for birds by running trails behind my house. Before I ever owned binoculars, my world revolved around the species I could see with the naked eye. Eventually, equipped with a small zoom camera, I discovered a world that held far more than Steller’s Jays, American Crows, and Mourning Doves (all of which I had my own names for). The world never changed, but as I learned more about it, it seemed to infinitely expand.
As I pinned more and more blurry photos of birds to my wall, I noticed something changing. What puzzled me was that each time I ventured out, I came across an always-changing array of birds. Brightly colored species I had never seen before would show up, then mysteriously disappear. I was no naturalist, so I assumed my methods were the cause. Ironically, running around haphazardly through the woods likely was a large factor in my inability to keep track of species. That’s when the “Kaufman Field Guide to Birds of North America” changed my life.
Within the book, next to the names of birds I had never heard of, were range maps of every species. In red was a bird’s breeding range, and in blue was the area it spent the winter. It was baffling to learn that the birds I assumed were my year-long neighbors sometimes spent winters in cloud forests close to the equator. They weren’t even “my birds” as I came to learn. Many of the species I associated my childhood with spent most of their time far outside of Washington’s temperate rainforest, and according to researchers, likely evolved in the neotropics before slowly expanding north.
Thousands of species totaling in the billions of individuals fly to different locations throughout the year. So many birds migrate during certain nights that radars can easily detect them. The same can be said for large movements of dragonflies. Most of this happens while we rest our heads at night. Not just birds undergo migration; mammals, fish, reptiles, amphibians and insects all make miraculous journeys as well. I say that migration is beautiful to admire because of its sheer magnitude, yet the finer details bring it to life.
One of the most common questions I am asked is, “How do they know where they are going?”
The literature grows daily with new reports of navigational brilliance by birds across the world. Whether it be songbirds using celestial cues on clear nights, shearwaters following smells across landmark-less oceans or even using magnetite to get a sense for the earth’s magnetic field. Despite these amazing feats, it doesn’t answer how they travel to places they’ve never been before.
In today’s world, Google maps feels necessary to make it anywhere. Before that, MapQuest and atlases held our hand in the art of navigation. Young birds embark on a flight that they must innately feel, alone and without Siri. For many of us, we get to follow our parents as they move around the world. This helps gather information and form our own cognitive map. A young bird is generally abandoned soon after it can feed itself, so it is forced to rely on its own empty map.
Curious scientists decided to experiment by moving birds from where they were born, and relocating them thousands of miles to see their response. Adult birds that had made successful migrations quickly realized the trickery and corrected their flight path to reach the usual destination. Young birds however did not notice the change, and therefore continued to fly at the same bearing and distance which landed them in locations the species should never be. Remarkably, if you were to plot the young bird’s flight path beginning from the correct start point, it would have landed in precisely the right spot.
The more I dove into understanding why birds move around, the more I realized migration has a much darker side. It is easier to admiringly look at a newly returned Black-headed Grosbeak than think about the thousands of identical ones that didn’t return. Migration is inherently dangerous.
Flying hundreds, thousands, even tens of thousands of miles can prove deadly. Estimates show around 50 percent of birds survive migration periods, easily making it the deadliest time of year for an individual. Dangers seemingly come from everywhere. Long trips require plenty of food, and many birds never reach their destinations due to a lack thereof. Emaciation and starvation can lead to easy predation or outright demise.
Ask a birder and they can tell you when each species is likely to show up, leave and be subsequently replaced by the next. This is because the timing of migration is as beautiful, cyclical and predictable as the flights themselves. However, some birds can also be caught “off schedule.” Environmental cues on breeding grounds may signal it is time to fly south, but climate change has disrupted this millennial-old act. If a bird leaves too early or late, they can be caught in unfavorable weather, winds and storms in areas that would generally be easily passed by.
Birds have evolved to accept exhaustion, predators, food shortage and severe weather as risks during migration, but there are dangers and risks birds have yet to adapt to. From large-scale factors like climate change to small-scale dangers like car and window collisions, birds face threats that drastically impact migrations that have been happening for millions of years.
Most small birds, unlike the Bar-tailed Godwit, stop often on their trips. Thus, quality habitats to forage and restore energy are essential to survival. Habitat conversion/loss throughout the country make this increasingly difficult. Nearly half of all land is agriculture, mainly for the purpose of raising cows or growing feed for them. Cities are also growing, and wetlands are rapidly being drained and paved over, leaving buried remnants of past ecosystems. Birds have been filtered into smaller and smaller areas that provide food necessary for survival.
Lights left on in cities overnight distract birds, especially those using celestial cues. They cause birds to drop down in altitude where they collide with glass buildings and windows. Growing numbers of volunteers help conduct surveys that attempt to determine exactly how many birds are killed like this each year. These groups also help push for bird-safe buildings. That includes having stickers, streamers or some sort of reflector in the window to warn birds. Additionally, lights out campaigns are starting across the country. This initiative advocates for turning lights off at night during migration. This is especially important in large cities and large buildings that easily distract and confuse migrating birds. Simply turning lights off can save our small, winged friends.
Birds will not stop migrating anytime soon. Humans will not stop living and expanding in the places we love. Improvement has to come in how we share the land. By watching and learning about the birds in your neighborhood, you are helping them. Senegalese environmentalist Baba Dioum once said, “In the end, we will conserve only what we love; we will love only what we understand and we will understand only what we are taught.”
My hope is that people may look around this spring, notice the arrival of the tiny world travelers and smile. Smile because they know at least a little more of the extraordinary journey each has completed, and the incredible dangers they avoided. Until they do it all again.
To learn more about migration and see maps of species that were GPS-tracked, visit explorer.audubon.org. To learn more about lights-out programs and what you can do, visit audubon.org/lights-out-program.
Ben Stalheim is a wildlife biologist from Bellingham, Washington. He travels the country to study the birdlife of the United States and explore new places.