It was the next to the last day of summer, the sky was blue with some haze on the horizon, and a pleasant breeze kept the biting insects away. When I stepped off the Harrington Trail onto the summit of Wachusett Mountain, I could see something interesting was happening on the deck of the fire tower.
Around 30 hawk-watchers, members of Eastern Massachusetts Hawk Watch (EMHW), armed with spotting scopes perched on tripods and binoculars, were calling out the names and numbers of migrating hawks. Someone shouted, “Fifteen broad-wingeds overhead!” Another called, “Bald eagle to the north!” A person with a clipboard, strolling the length of the deck, was recording it all. But the broad-winged hawks were the stars of the show.
(Photos by Lisa Aciukewicz)
Bird migration is not completely understood. From the information gathered by tiny GPS geolocators and other technologies attached to birds captured and released in the field and the results of biological research done in labs, birds appear to live in another world. The research has revealed that some birds travel many more thousands of miles than was previously thought. Another discovery is that the birds studied appear to be able to build specific muscle tissue for their journey without exercising. Birds are also able to fly those many thousands of miles without sleep because of an ability to shut down portions of their brains, a trait shared by some sea mammals. But will we ever understand how they navigate around the globe to their destinations?
The Hawk Migration Association of North America (HMANA) gathers facts from volunteer citizen scientists and maintains a database, HawkCount, with input from over 300 North American hawk-watch sites, including those in Canada and Mexico. The names and numbers of hawks sighted, weather details, flight height, hours of observation, number of observers, short narratives describing the day, and even the number of some migrating non-raptors, including monarch butterflies, are recorded daily during peak migration times.
The day before my visit, the watchers recorded 1,186 hawks, but the next day when I was there, just 168 hawks were recorded, although watchers at Pack Monadnock and Mount Watatic, both almost within eyesight from the landing on the fire tower, recorded 1,112 and 776 hawks, respectively.
The day of my visit, an observer explained that the wind is the main factor in determining the flight path the hawks will take, a north or northwest tailwind being the most favorable for sighting flights over Wachusett. Lately, the number of sightings in Massachusetts has dropped because early- to mid- September is the peak time for the hawk migration in our area. Southeastern sites are now recording the high numbers of sightings.
Kettling
An observer suggested I look for “kettling.” Perhaps you’ve seen a turkey vulture flying in an upward spiraling pattern until it reaches a certain height and then it breaks away, soaring into the distance. These big birds use warm updrafting winds, called thermals, to achieve lift. When large numbers of broad-winged hawks, vultures, and other raptors flock together in these winds, spiraling to the top of a thermal, they appear to create a tornado-like shape. This is called a “kettle.”
Looking into the expanse of blue sky, I saw emptiness, but when invited to look through a scope, I did see a moving dark speck. I could tell it was probably a bird, but the experienced hawk-watchers were identifying just such a speck by certain basic characteristics of silhouette shapes and flight style. Birds’ intent can also be ascertained by their flight patterns. An observer explained that some red-tailed hawks stay local and can be visually sorted out from those migrating by their flight style.
After looking through the scope, I understood that plumage is less reliable as an identifying feature because lighting and distance can obscure those features. The hawk-watchers laughingly admitted that despite their obvious camaraderie, they do get into disputes about the identification of their sightings. As the people on the deck of the fire tower on Wachusett lifted their eyes and binoculars skyward, it felt as though they were wishing a bon voyage for the birds embarking on their formidable and mysterious journey to Earth’s southern hemisphere.
With scopes and binoculars, bird-watchers keep their eyes on the skies for migrating raptors.
For more information
Eastern Massachusetts Hawk Watch: www.massbird.org/EMHW
The Hawk Migration Association of North America provides data from more than 300 North American Hawkwatch sites: www.hmana.org and www.hawkcount.org
The two guidebooks used by the observers emphasize how the birds appear in the sky, rather than in close-up illustrations:
- “Hawks at a Distance: Identification of Migrant Raptors” by Jerry Liguori. Princeton University Press, 2011.
- “The Crossley ID Guide: Raptors” by Richard Crossley, Jerry Liguori, and Brian Sullivan. Princeton University Press, 2013.
For reading about the current knowledge of bird migration, this book is rewarding—even if you just read the preface: “A World on the Wing: The Global Odyssey of Migratory Birds” by Scott Weidensaul. W. W. Norton and Co., 2021.
