I woke up early this morning, excited to drive up the mountain. After a short hike to the rocky overlook, I set up my spotting scope and trusty binoculars. This peak towers over the forested valley and allows views of the mountain ridges as far as the eye can see. Out of thin air, a large hawk soars out into the open. It streaks quickly across the sky until it begins a gentle upwards ascent on an air thermal. It flies overhead, fanning and tilting its tail like a rudder, narrow bands of black and white stretching across the tail feathers. Another hawk joins in, then another, and another. Suddenly, dozens of birds are criss-crossing and swirling in the invisible column of warm air. One by one, each hawk breaks away and speeds down the mountain ridge until they gracefully rise yet again into the endless sky. This intriguing pattern is none other than the migration of the Broad-winged Hawk (Buteo platypterus).
When soaring, the Broad-winged Hawk can be easily recognized by its shape and pattern. Adults have fine, horizontal streaking across the breast, black borders along the trailing edge of the wing, and black and white barring across the tail. Juveniles look very similar except the tail is marked with distinctly narrower lines and the barring across the breast is more variable. Dark morph individuals are less recognizable. They possess dark brown plumage over nearly their entire bodies, except for the white tail bands. Like other Buteo hawks, its silhouette can be described as stout with large, bulky wings and rounded tail. Accipiters and falcons generally have a different body form. Accipiters, like Cooper’s and Sharp-shinned Hawks, have longer tails and narrower wings. Falcons are generally recognized by having long, tapering wings and a stronger flight pattern than Buteos. Broad-wings are similar in appearance to Red-tailed Hawks (Buteo jamaicensis), Red-shouldered Hawks (Buteo lineatus), and Cooper’s Hawks (Accipiter cooperii).
During the breeding season, they call the deciduous forests and wooded edges of Eastern US and Southern Canada home. They munch on a number of woodland creatures, both vertebrates and invertebrates. Birds, small mammals, amphibians, reptiles, and insects make up a large portion of their diet. Many times, I have encountered Broad-wings perched in the woods, poised to drop to the forest floor at any moment in pursuit of prey. The abundance of trees and branches in our woodlands provide the perfect vantage point for scoping out an unsuspecting victim. Broad-wings call occasionally, giving a high-pitched, whistled “pur-ee.” This sound is anything but the intense screech that many people associate with formidable birds of prey!
The journey between their breeding grounds in the United States and wintering grounds in Central and South America is perhaps the most captivating aspect of the Broad-wing’s life history. Thousands of enthusiastic birders gather at observation points along their migration route to take part in annual hawk watching events. The Hawk Migration Association of North America (HMANA) has played a huge role in organizing volunteer-sourced data for extensive research (and appreciation!) of the movements of migratory raptors in North America.
Observing a migrating Broad-winged Hawk is truly fascinating. Traveling hundreds of miles is energetically taxing, so, if at all possible, hawks try to avoid burning valuable energy on flapping. How is it possible for them to voyage across the continent without flapping the whole way?
The answer: thermals!
The incredible phenomenon of raptor migration is made possible by the simple heating of air by the sun. As the sun begins to climb in the morning, surfaces like mountain ridges warm up and heat the above air. The newly warmed air rises above the cooler surrounding air. This creates columns of rising air called “thermals,” which are the key ingredient for raptor migration. Raptors often fly into a thermal, passively circle to the top of the air column, break away once they have achieved enough lift, then soar until they encounter another thermal. Dozens, hundreds, even thousands of hawks can join into one thermal. These large groups are referred to as “kettles.”
Broad-winged Hawk populations appear to be doing very well. Over the past several decades, it seems that their numbers have remained relatively stable and might even be increasing in some locations. Breeding habitat is probably increasing in North America due to the succession of abandoned farmlands. Sadly, habitat destruction, hunting, and car collisions are still an issue for birds on their wintering grounds. In fact, the Puerto Rican population is currently on the Watch List of the Endangered Species Act.
Raptor migration in our region lasts from early September through early October. There is still some time to grab your binoculars and head out to a local hawkwatch near you!