Laura Erickson's For the Birds

Rachel Carson wrote that “There is symbolic as well as actual beauty in the migration of birds. There is something infinitely healing in the repeated refrains of nature–the assurance that dawn comes after night, and spring after the winter.” Many Minnesotans find special joy in the migration of hawks. Their annual rhythm, which has no beginning and no end, brings us hope in spring, as hawks return on March and April warm fronts to produce new little hawks, and a sense of fulfillment and satisfaction in autumn, as these hawks, their numbers augmented by this year’s young ones, head south once again.

Of course, that’s pretty much the way of all migratory birds. Hawk migration is special because these birds, exuding fierce and uncompromising wildness, migrate by day when we can see them. And unlike geese and other conspicuous daytime migrants, they don’t move past us as fast as they can flap their wings. Instead, hawks mosey on through, flying in circles as they rise on vertical air currents called thermals. Thermals can form over any spot of land that is a few degrees warmer than its surroundings. Thermals are strongest in the land beside water and above pavement, and in fields next to forests. And anywhere where a thermal forms, we can savor hawk migration, watching them spiraling in one area for many long minutes before each hawk reaches the top of the thermal and streams forward to find another one..

We humans, with our solid bones and thick hides, can feel many air currents against our skin, but the currents need to be pretty stiff for our movements to be affected by them. Hawks have hollow bones. And their feather-light wings, fully spread, have so much surface area relative to their weight that their bodies are buffeted by very slight air currents. As hawks labor forward in flapping flight, their bodies sense a thermal the way our bodies sense a heavy wind, and they suddenly switch to gliding flight, circling to gain altitude. Most hawk species are not particularly sociable, but during migration, they often locate thermals by watching for other hawks spiraling on these invisible currents. When a group of hawks spirals on the same thermal, we call the gathering a kettle. Sometimes there are only a handful of hawks in a kettle, sometimes over a thousand. When kettles are large, they resemble swirling tornadoes of birds.

In September, kettles can form anywhere in Minnesota. So why do we think of Duluth when we think of hawk migration? Because Lake Superior is so huge. Thermals form all along the shoreline. Hawks from a huge swath of western and central Canada and Alaska, as well as the from the plains states, are pushed by prevailing westerly winds toward Lake Superior, and wherever along the north shore they find themselves, they follow the shoreline along until they clear the lake. Why are they reluctant to fly over water? Thermals don’t form over water, so they’d have to flap the entire distance. And downdrafts, which are sort of the opposite condition, do form over the lake, and could literally drive hawks down into the water. Hawks can be observed migrating along the entire shoreline, but are most abundant at the end of the line, and Hawk Ridge in Duluth provides a perfect vantage point for watching them.

Any time in September or October you can see hawks in Duluth. But flights can be tiny or virtually non-existent when it’s raining or the winds are easterly. Rising barometric pressure and winds forcing birds along the shore provide perfect conditions when the wind has a westerly component, with northwest winds being perfect. On September 18, 1994, a total of 49,615 hawks were recorded flying over the main overlook, the biggest day ever at the Ridge. In a normal season, about 93,000 hawks are recorded from August 15 through November. The biggest days are in mid-September.

But hawk migration doesn’t end in Duluth. After clearing the lake, some hawks follow I-35, riding on thermals above the highway. Others follow the shoreline of the St. Louis River or just head generally south picking up thermals as they find them. In the Twin Cities, I’ve seen kettles over downtown parking lots and buildings, along the rivers, and above busy highways. What Twin Cities hawk migration lacks in predictability it makes up for with the unexpected delight of finding a tornado of hawks in the heart of a busy city.