More About Migration!
A couple days ago, while walking to work, I was fortunate enough to cross paths with a pair of Northern Cardinals. I felt so lucky to have been so close to them that a smile was on my face until I went to bed that night. Has anything similar happened to you recently? Have you seen birds that easily light up your day with their flitting movements and cheery songs?
As I thought about Northern Cardinals that night, which stay in Ithaca the whole winter (Northern Cardinals are non-migratory), I wondered when our migratory birds would return from their wintering grounds. Not only does the arrival of migratory birds increase the diversity of birds in our area, but their songs also give a very unique life to our springtime. Migrants allow us to connect to nature with a special sort of happiness and vitality. Have you ever asked yourself how these birds prepare for such long migratory flights when it can take some of us days just to prepare one suitcase for a weekend trip?
Well, first of all, they become gluttons. Yes, they eat almost without restraint. Even if you don’t believe it (or perhaps you’re starting to like the sound of the idea yourself), a bird that is about to migrate alters its diet so drastically that it eats about 30% more than normal in calories, with a special appetite for fatty foods. This change in diet makes the bird’s digestion and metabolism more efficient, increasing the bird’s fat stores by almost half its body weight. The human equivalent would be a 150lb person gaining 75lbs by the end of a month. Can you imagine such a transformation? It is almost too incredible! Still harder to believe is the fact that in the time it takes the bird to migrate, which is one or two weeks, the bird will lose almost all the fat they gained. Talk about a yo-yo diet!
But why is so much fat important to a bird about to migrate? One might think that such an increase in weight might negatively impact a bird’s flight ability, like an airplane that has taken on too much luggage. The difference is that the birds have overloaded themselves with what is practically pure energy and water—resources that are imperative for the thousands of miles of flight between winter homes and breeding grounds that some species undertake. Although it may not look it by the time they get here, our migratory birds will have become little balls of fat and water before they leave their wintering sites. Can you imagine how hot they must get on the way over here? Don’t forget that they’re covered in feathers (we all know how warm a down comforter can be)!
Since the exertion of flying produces so much heat, birds can become dehydrated on long flights, the way your levels of thirst will differ between running around your neighborhood block and completing a half-marathon. Normally birds do their migratory flying at night, because one of the simplest ways to control dehydration is by flying in currents of cold air, which are easily found at great heights, or when the sun is down. Another reason for flying at night is to use the stars as guides and avoid predators. I find that the former motive provides a more beautiful image: birds still follow the stars the way our greatest navigators circled the globe centuries ago—think Marco Polo or Ferdinand Magellan. But these explorers also used compasses to get around, didn’t they? Well, it is likely that some birds have something similar to an internal compass that allows them to detect surrounding magnetic fields and use them as pointers on migratory flights.
Of course, it seems like it’d still be easier to fly by day. If you’ve ever had to drive through the night to visit your relatives for Thanksgiving, you know how horrible nighttime orienteering can get (and I’m sure Magellan and Polo enjoyed having the information the sun can provide, too). So yes, some migratory birds prefer to fly by day. These birds tend to use the position of the sun (many birds might be able to see polarized light, making this easier even on cloudy days), cues from surrounding terrain, the magnetic fields, and, though you may be skeptical again, smells and sounds. There is reason to believe that homing pigeons can hear infrasound, allowing them to detect extremely low frequency sounds the way elephants do, and some scientists think birds can differentiate large-scale odor changes over long distances (say, thousands of miles). I should point out that this latter claim is a bit controversial—although some scientists have a little evidence supporting the hypothesis, many have yet to concur. So as you can see, there are still many questions about bird migration. I’ve only told you a bit about what is known, or at least thought, regarding how migratory birds fly every year between breeding grounds and winter sites; there is still much to learn.
So go out for a walk in the park near your house. Look out the window. Step onto your porch or balcony and plant some flowers or beautiful bushes in your backyard, and enjoy the birds that will visit you. Maybe upon seeing them your day will improve as quickly as mine did when I came across the Northern Cardinals, and you will think of another reason for birds migrating, or how they do so. And if something does occur to you, or any artwork is inspired by your encounters, share! Remember that we are still accepting your spring creations and photographs—find the Signs of Spring challenge here: http://www.birds.cornell.edu/celebration/challenge/signs-of-spring-1
Until next time!