Swirling columns of migrating hawks

Written by Jack Sanders
Thursday, 23 September 2010 13:09

From September, 2010:

“Not sure exactly what I saw today — at about 11 a.m. on the 16th  a large sort of flock of what I think were hawks,” writes Chris Dahm  of Umpawaug Road in Redding. “There had to be a couple of hundred flying in a swirling column northwest of my location on Umpawaug.  I put my binoculars on them for a few seconds.  Definitely large raptor type birds with what seemed like a white-hued tail. They were sort of flying at each other but not too aggressive.  This column continued as it spiraled towards say Ridgefield.  I would say the altitude was 1,000 feet plus.  I have never seen anything like this before — any ideas?”

Chris was probably seeing migrating hawks.

The day after he saw these birds, Luke Tiller at Audubon Greenwich reported more than 1,000 Broad-winged Hawks passed over the hawk-watching location at Quaker Ridge.  This is the season for mass migration of some species of hawks — but not our common Red-tailed, or the smaller Cooper’s and Sharp-shinned, which remain here year round.

In general, birds that rely solely on “powered” flight — that is, constantly flapping their wings — tend to migrate by night while those that do some gliding or soaring travel by day.

Daytime would seem the simplest time to travel since visibility is good and most birds are active in the daytime anyway. But the sun that provides the light also creates heat, and a bird that is flying hundreds of miles is already hot from burning so much energy. The added heat of the sun could dehydrate a wing-beating bird quickly.

However, such birds as hawks, swallows, cranes, and storks, travel by day to take advantage of thermals, rising columns of air created by the sun’s heating the earth, that help keep them aloft. These same currents would be disturbing to a long-distance powered flyer, adding to the effort it takes to move through the atmosphere in a straight line. Thus, nocturnal flight tends to be smoother, with less energy wasted on combating currents.

Migration affects wing size. Birds that travel long distances have stronger wings than those that do short migrations or remain in the same territory year round.  The size of the wings of different hawks reflects both lifestyle and migratory habits. The Sharp-shinned Hawk has relatively short wings compared to many larger hawks. That’s because it preys on flying birds. It pursues agile prey much smaller than itself and it must be at least equally agile to catch a bird on the wing, especially through the maze of obstacles presented by woods.

While Sharpies sit and watch for prey, many other hawks search out food from high in the sky, often gliding through the air. Their long, broad wings are designed to keep them aloft with relatively little effort as they inspect vast stretches of ground below. They must swoop down on prey only in open areas, such as fields; their wings could not maneuver in tight spaces like forests.

Such hawks as the appropriately named Broad-winged Hawk, use their soaring abilities during migration, following routes where updrafts are plentiful. Flapping is kept to a minimum and these migrating hawks can travel long distances using relatively little energy.

Crashing warblers

Speaking of migration, Mary Walsh of Ridgefield reports, “Over the past few days three different warblers have collided into my picture window.  I had hoped that each of them were in temporary shock and would revive themselves, but unfortunately this did not happen.  I usually don’t see warblers at the feeders, but for some reason they are attempting to try the feeders only to find that they are not very good at navigating around windows.  I had to get my guidebook out to identify them.  A Black-throated Blue Warbler, a Black-and-White Warbler and this morning a Tennessee Warbler had an unfortunate mishap with a window.  Is it common for these birds to eat at feeders?  They are definitely not part of the daily nibblers.”

No doubt, these warblers were migrating through. Warblers are basically insect-eaters, which is why you’d rarely see them at a feeder — except, perhaps, in migration times. The Smithsonian Migratory Bird Center reports, “During migration, Tennessee Warblers make extensive use of energy-rich fruit resources as well as insects. This small warbler is limited in the size of fruit it can fit into its tiny bill. Consequently, they are more abundant in second-growth and open forests, which generally have trees and vines with small bird-dispersed fruit.” If a feeder has hulled sunflower seeds, it may bring in some warblers!

Keeping them from colliding with the windows requires a little effort. We usually suggest dulling the outside of the window with soap or Glass Wax, dangling strings, or sticking up plastic appliqués. There are also specialty devices for this available in bird stores.

Coming up

Autumn Morning Bird Walks: Saturdays, Sept. 25, Oct. 2, 9, 16, 23, 30; Wednesdays, Sept.  29 and Oct. 6, 13, 7:30, free, Audubon Greenwich, 613 Riversville Road, Greenwich.audubon.org, 203-869-5272 x221.

Autumn Birding Series, trips and talks with Luke Tiller: “Confusing Fall Warblers” lecture (Sept. 23) and trip to Greenwich Point (Sept. 26); “Raptor Migration” lecture (Oct. 14) and trip to Lighthouse Point (Oct. 17); “Little Brown Jobs” lecture (Oct. 21) and trip to Allen’s Meadows (Oct. 24); talks Thursdays at 7 p.m. , trips   at 7:30 am;   $15 per lecture/trip or $60 for all six;   RSVP to store: 203-869-5272 x221 Audubon Greenwich, 613 Riversville Road, Greenwich.audubon.org

Great Stratford Bird Festival, keynote speech by Phil Donahue, dozens of talks, walks, field trips, exhibits, food, programs for kids, etc., Thursday, Sept. 23, through Sunday, Sept. 26; stratfordbirdfestival.com.

Fall migration at Chestnut Ridge Hawk Watch, Sunday, Sept. 26, 9 to 11:30, Bedford Audubon,  at Butler Sanctuary, Chestnut Ridge Road, Bedford Corners, N.Y., 914-666-8448, bedfordaudubon.org

Copyright 2010 by Jack Sanders. Send sightings or comments to: jackfsanders [at sign] yahoo.com, or to Bird Notes, Box 1019, Ridgefield, CT 06877; or call 203-438-1183, extension BIRD (2473), and leave a message with your report, spelling your first and last names and telling us your town. If you need help identifying a bird, try your local nature center. If you find an injured bird, call wildlife rehabilitator Darlene Wimbrow of Redding, 203-438-0618, Wildlife in Crisis of Weston, 203-544-9913, or Wild Wings of Greenwich, 203-637-9822. The columnist’s website is www. sandersbooks. com.