Broad-winged Hawk

Broad-winged Hawks reach their peak migration between September 10 and September 20. In anticipation of potentially seeing hundreds of hawks in a single day, hawk watchers have crowded Putney Mountain this week. As of mid-week when I wrote this, they have not been disappointed.

Buteos are the genus of hawks characterized by their broad wings, short tails, and soaring ability. The Broad-winged Hawk is our smallest buteo, with a body length of 15 inches, wing span of 34 inches, and weight of 14 ounces. By contrast, the familiar roadside hawk, the Red-tailed Hawk has a length of 19 inches, wing span of 49 inches, and weight of 2.4 pounds. (Measurements are from Sibley’s Guide and are approximate.)

The Broad-winged Hawk is a forest species that seldom draws attention to itself and often goes unnoticed unless someone knows it and searches for it. Its cousin, the Red-tailed Hawk was often known as the hen hawk for its opportunistic taking of farmyard birds. The Broad-winged never acquired such a nick-name because it rarely troubled with the farmer’s poultry or pigeons.

In spring migration and summer breeding, the Broad-winged can be completely over-looked, although the attentive person may hear its thin piercing whistle, “eeh-eeeeeeee.” Then it is time to look high. “In warm summer weather it frequently soars to great heights with widely extended and almost motionless wings ... Possibly no hawk ascends higher in the heavens than this rather small, inconspicuous species. Its broad, ample ‘clubbed’ wings, which name the bird so aptly when they are well seen, often make this hawk seem larger than it really it.” (Forbush)

As inconspicuous as the Broad-winged Hawk is during the summer, at the right place and right time during September it is the dominant hawk species. The birds lift out of their Northeastern woodlands and begin their journey south. They will travel thousands of miles.

A single bird rises above the forest canopy. Its hawk eyes see another bird circling upward, the second bird having found rising warm air. The first bird joins the second, then a third joins the two, then a fourth. And so it goes, the birds gathering, not as a flock for safety, but as a loose group taking advantage of the same flying conditions - rising thermals, ridge-line updrafts, and favorable winds. With good conditions, a Broad-winged Hawk is capable of traveling a couple of hundred miles in a day with barely a wingbeat.

Putney Mountain is one of those places where the conditions are often favorable. On a good day five hundred, or even a thousand, broadies might be seen. In comparison to some eastern watch sites, those numbers are not so impressive. Places like Duluth, Minnesota, Hamilton, Ontario, Hawk Mountain in Pennsylvania, and (erratically) some mountains in Massachusetts, can have single day numbers in the thousands, or even tens of thousands. As the flyways converge in Corpus Christie, Texas or Veracruz, Mexico, the numbers can swell to hundreds of thousands.

The visiting “hawk snob” from some other “bigger and better” site might be disappointed with “only” five hundred Broad-winged Hawks in a day. But I have yet to hear any local hawk watcher on Putney Mountain who is disappointed with such numbers. When these inconspicuous forest hawks begin streaming over the ridge, or circling up by the dozens, there is excitement. There is wonderment. Where did they all come from? And of course, there is the puzzle: where are they going?

There is some good research about where the Broad-winged Hawks are going, and the impressive travels they undertake in the going and coming. The short answer is that the broadies are headed to the tropics - Central and South America.

Research has shown that the journey of the Broad-winged Hawk is as spectacular as its numbers in migration. Five adult females were fitted with radio tags at their nesting locations in north-central Minnesota and western Maryland in the Spring, 2000. With satellite telemetry, the hawks could be tracked for many months and thousands of miles. With luck, every zig-zag in their route could be tracked, where it stopped, for how long it stopped, and where migration ended.

Four of the adult female Broad-winged Hawks were tracked along their entire fall migration route. The fifth was out of contact until the next spring when she was halfway through her migration back to Minnesota.

The other four left their breeding grounds in September. They followed the expected path south, “converging in Texas, following the Gulf Coast into Mexico, passing over the famous hawkwatch in Veracruz, and taking an inland course through Central America.” One bird stopped in Panama and wintered there. Three continued to Colombia where one veered east into Venezuela. The other two traveled south of the equator and wintered in southwestern Brazil and southern Peru.

The radio tagged Broad-winged Hawks traveled between 3,500 and 4,800 miles. Daily travel was 50 to 75 miles per day. They reached their wintering areas between October 15 and December 15.

“Because of radio failures, only one bird could be tracked completely during its spring migration northward.” She flew 4,878 miles in 74 days from Peru to Maryland, where she arrived on May 22 at the same nesting location from which she had departed eight months earlier. Her total round trip was about 9,700 miles.

Yet another question often asked about Broad-winged Hawks is: What do they eat along the way? A more precise question would be: Do they eat on their migratory journey? On Putney Mountain, we occasionally see a low flying Broad-winged with a full crop, clear evidence that it has eaten recently. This week I have watched several Broad-winged Hawks stoop into the tree tops just below the ridge, as though they were diving after possible prey. But as the migrating hawks concentrate in Texas and Mexico into the hundreds of thousands (even millions), is there enough food? Or do they “fast” for a portion of their journey? I have yet to find research which addresses this question. So ... when there are no hawks to watch on Putney Mountain, we can discuss this question without having to worry about facts.

Good Birding!

Information for this column and quotations are from “Tracking Hawks’ Migration Patterns” by Paul Hess in “Birding”, October, 2004.