Night Flight

Most of us never consider going birding at night -- why bother? You can’t see the birds, they’re not singing, and except for owls (and a few others) they’re not active anyhow. Birds pretty much sleep at night and fly during the day, right?

Wrong! Many small birds, including popular favorites like warblers, sparrows, orioles, grosbeaks and tanagers, migrate at night. Right now, on clear fall nights, millions of birds are streaming south on their migrations.

You might be amazed how many are flying right over your house -- step outside tonight and check it out!

Most are moving 100 to 500 feet overhead. And they’re not silent. They call to each other constantly with short notes called flight calls. If you stand outside and listen you can hear them, and maybe even see them silhouetted against the moon.

Why do birds migrate at night?
It might seem counterintuitive for birds to migrate long distances at night. After all, like us they can’t see very well in darkness. But overall the “night flight” strategy has worked for millions of years.

One benefit for smaller birds to flying at night is that there are no raptors waiting to pounce on them. Hawks are only active during the day, and owls generally perch-hunt for rodents and other ground-dwelling prey, rather than trying to catch other birds on the wing.

Another reason is that the atmosphere tends to be more calm and stable at night. For example, there are no rising columns of thermal air, and hence less turbulence overall. So the small birds can fly more efficiently at night.

The cooler nighttime air temperatures also help the mighty little migrants. Flying for hours on end, at 20 to 40 miles per hour, they burn up a lot of energy, and this can make their bodies overheat -- just like yours would if you were running a marathon.

Celestial navigators
But so what if it’s cool and safe? How can the birds stay on course as they wing along for hundreds of miles through the darkness? Amazingly, many can navigate by the stars. Ingenious experiments going back many years have shown this conclusively.

Many birds have a sense of both the configuration of stars in the sky where they are, as well as a time sense that relates the position of celestial objects to the geography below them. Little birds know the right direction in which to orient themselves just by glimpsing the night sky.

And with no experience to guide them, young birds making their first migrations can arrive safely at a place they’ve never been, by a route they’ve never taken. Taking their cues mostly by the stars. Wow.

How do they do it? Nobody knows all the facts for sure. Part of the process is likely instinctive and inherited. But part is almost certainly learned. Sitting in their nests at night, baby birds are learning the configurations of the night sky! Apparently they can judge that the stars closest to the Pole Star move the slowest; and they can note other general patterns as well -- enough to internalize a compass to guide their sense of direction.

Of course, sometimes they miscalculate. Here on the east coast, especially on nights with strong “cold fronts” bring brisk northwest winds, unfortunate birds may find themselves out over the ocean at dawn. Some find the coast or make for offshore islands. A few even find temporary refuge on passing ships. (Bring mealworms if you’re making an ocean voyage at this time of year!)

But many wander far out at sea, eventually succumbing exhaustion and drowning. And predators like gulls and Peregrine Falcons roam the inshore waters, nabbing hapless migrants. Life is not easy for our dear little friends…

Birding after dark
So how does one approach birding at night? The same basic ways we bird during the day -- by sound and sight.

One way to spot night-flying migrants is to train a spotting scope, telescope or binoculars on the moon -- especially when it’s full. Crank up the magnification and you can see silhouettes of migrants, both individuals and groups, from quite a distance. (Some say up to two miles.) With a little practice you can learn to identify, or at least make a guess about, what family a bird is from by its silhouette.

The other way is to learn the flight notes of the migrants. Folks who get good at this can identify birds to family type and sometimes even to species as they zip overhead. (Some calls, like those of the thrushes, are easier to learn than others.) Research has led to the creation of a CD for this purpose, called Flight Calls of Migratory Birds for eastern North America. Check it out: view link

Night-birding is “happening” from August through October, when tens of millions of birds are on the move every night. Weather plays an important role: migrants will sit tight waiting for good conditions, when it’s calm or there’s a light tailwind, and possibly when clouds don’t obscure their celestial reference points. Clear nights free of massive weather systems, such as when a front has just passed through, are often best.

You can start your nighttime birding about a half-hour after sunset, to catch the birds departing your local area. By the “wee hours” you’ll be hearing birds that began their flight hundreds of miles to the north.

How many migrant birds fly over your house at night in the fall? Spend some time outside counting, and extrapolate “calls per minute” over the number of hours in the night. It could be literally thousands of birds! Even in an ordinary, “nothing special” spot.

There’s only one way to find out -- get out there! Night birding is a lot of fun! If nothing else, it inspires an even deeper appreciation of the birds.

Links of potential interest

A cool web page on birds’ nocturnal calls from the Cornell Lab of Ornithology:
view link

“Stars of Navigation” from birdwatching.com: view link

From the Chipper Woods Bird Observatory:
view link

A cute piece on birds and ants “using math” to navigate:
view link

Peace and good birding,
Scott Cronenweth
Eons birding mentor
www.naturalpathwalks.com