Monday, October 5, 2015

Broad-winged Hawk

Migration Spectacle 

Broad-winged Hawk - Adult
The Broad-winged Hawk is a common woodland hawk in our area in summer.  It breeds here and in the rest of southern Canada from Alberta eastward as well as in eastern United States.  We hear it more often than we see it during summer with its distinctive high-pitched whistle.  It is in the fall that this species becomes famous.  It gathers in flocks or 'kettles' to migrate down the eastern coast, through Central America to its wintering grounds in northwestern South America.  Because it does not like to fly over water it follows the coast southward.  This spectacle does not occur in the spring because in the northward migration it flies over various inland routes.

To migrate the birds use natural updrafts or thermals in the atmosphere.  These are areas where the air is moving upwards caused by temperature differences or winds.  This makes flying easier and allows them to gain altitude.  In these updrafts the birds gather in kettles or groups and then move off on their southward journey.  After they reach maximum altitude, they can then fly by winging or by soaring on south winds, slowly losing altitude but covering large distances.  When they reach the next updraft, they repeat the process.  Updrafts are caused by land masses like mountains, large hills or ravines which cause the air masses to move upwards.  It is these areas where birders gather to see the concentration of migrating hawks.  See the photo below which shows kettles of hawks spiralling upwards or perhaps waiting for favourable winds before moving southward.  Research shows that these birds migrate about 4,300 miles (6800 Km) in total and about 70 miles a day (110 Km).

Migrating Hawks [Wikipedia Photo]
The Broad-winged Hawk is the smallest member of the Buteo family.  Other Buteo species that we have in New Brunswick are the Red-tailed Hawk, the Red-shouldered Hawk and the Rough-legged Hawk.  The Broad-winged Hawks get their name from the fact that the secondary feathers in their wings do not bulge outward like they do in the other species.  Their general shape shows a broad wing and a smallish tail.

Adults have a mottled dark brown back with reddish-brown streaked upper breast and white belly with some streaking.  The tail is  black with wide white bars.  The juvenile shows a white breast with some streaking.  See the photo above for the adult and below for the juvenile.

Broad-winged Hawk - Juvenile
Hawk watchers have seen thousands of these birds migrating through New Brunswick this fall.  One viewing area is from Greenlaw Mountain near St. Andrews.  One memorable sighting for me was a few years ago when I was standing in the woods near the coast at Coleson Cove and above me I began to see Broad-winged Hawks silently soaring just above the trees.  I counted over 20 birds as they circled overhead.  I felt privileged to observe this spectacle.

No comments:

Post a Comment