Spring migration is here!
I knew spring had arrived when a dashing little song sparrow startled me with song during my morning walk on February 17. Yes, I know that seems a bit early, but for many birds February marks the beginning of the breeding season and it’s a time that must not be wasted. Thousands of migrating ducks arrive to my local wetlands in February and March. Every moment is spent foraging, claiming territory, and searching for a mate.
Now, spring really has sprung! Migration is in full swing. Though many species arrived to my area earlier this month, our peak migration is expected to occur during the last week of April and first week of May. But what if you don’t live in the Pacific Northwest? When’s your best chance to see the waves of warblers and other colorful feathered visitors?
Thanks to BirdCast, a cooperative effort between eBird (Cornell Lab of Ornithology) and Colorado State University, you can explore nightly migration forecasts through June 15. It turns out that the technology developed for weather surveillance happens to work quite well for detecting birds. You can also visit this article to see this year’s biggest migration booms by region. Tonight, over 330 million – yes, million – birds are predicted to take to the skies across the country.
Not all hepatic tanagers migrate; this female may travel from Central America to Southern Arizona in the spring to breed, or she could be a year-round Arizona resident.
Why do birds migrate at night?
Migration is a risky business full of predators, obstacles, and severe weather. Flying during the day often requires more work, because the air is less stable (due to sun-heated thermals) and more predators are about. During the evening hours, the air currents are calmer and the skies are safer. Many birds also use the stars to help navigate, which you can’t spot during the day! Flying by moonlight still requires energy-budgeting and strategic routes for birds to successfully reach their destination. That’s why so many birds visit stopover sites. These areas are often wetlands, mudflats, and other nutrient-rich areas where the birds can gorge themselves on prey and continue along their journey, fueled for the next leg.
Why do birds migrate when they do?
Timing is crucial: birds have to arrive at the right location at the right time if they are to have enough food. Contrary to popular belief, birds don’t fly south for the winter because it’s getting colder; not directly, that is. Colder temperatures mean a sharp decline in prey populations like insects, which then means birds need to move in search of food. This is why they time their migrations with spring and fall. When weather turns for the worse in Washington, Swainson’s hawks head to central and south America. They return in the summer to raise their chicks while feasting on our seasonal abundance of rodents and small birds. Surprised that hawks migrate? Though goldfinches and bluebirds often first come to mind, migration is a phenomenon found across a myriad of avian species. From falcons to vultures, raptors often travel along mountain ranges to take advantage of thermal currents rising off the terrain. They act as a highway of sorts, saving the birds energy on their long haul trips. Such highways are so attractive that many raptors often end up traveling the same routes simultaneously, forming large groups called kettles.
Mighty hummers
Hummingbirds are one of the most impressive groups of migrating birds in my area. In my neighborhood, they are often some of the first to show up. Considering their high metabolism, it’s amazing how far they can travel at once! Hummers eat insects and nectar, usually needing a meal every 10 to 20 minutes. However, during migration, they fast periodically and can travel over 20 miles per day. Taking it to another level, ruby-throated hummingbirds cross the Gulf of Mexico–a 500-mile expanse of ocean–nonstop. It takes around 18 hours if the weather is on their side.
You can aid migrating birds by keeping feeders full (and clean, to prevent the spread of disease), planting native blooms, and turning off your lights at night. Light pollution makes it more difficult to see the stars, and can be severely disorienting for birds, especially in big cities.
What birds are you looking forward to most? I’m counting the days ‘till the flycatchers arrive. Until then, I’ll be watching warblers!
I saw this rufous-tailed hummingbird in Costa Rica, where he posed for a portrait. This is a rare species in the U.S., since the northernmost part of its breeding range just barely reaches into southern Arizona.
