Why most migrants head north for summer

Written by Jack Sanders
Thursday, 06 October 2011 11:09

It’s the height of the migration season, a time when billions of bird calories are being burned to get from one place to another.

When we think of migration, we typically think “north-south.” And, in fact, the vast majority of the world’s birds migrate from south to north in the spring, and vice versa in the fall. But many fewer do the opposite — go south when it’s summer in the Southern Hemisphere.

Inspect a globe and the reason becomes clear. The Northern Hemisphere has much more land mass than does the Southern Hemisphere. Many more migrants that winter south of and around the equator will head for the “wide open spaces” of United States and Canada than for the narrow tail of southern Argentina and Chile. In fact, while many birds that winter south of the equator fly north for the summer, not one species that winters north of the equator flies south for the Southern Hemisphere’s summer.

Not all birds migrate north-south, either A few may move east-west. Blue-winged Teals that breed in Plains states like Kansas and Nebraska may fly east to spend the winter on the coast of Virginia or the Carolinas. Purple Finches that summer in northern Michigan may winter in New England. The White-winged Scoter may breed in western Canada and winter on the East Coast of Canada.

There are not only different directions for migrations, but different kinds. In his book, How Birds Migrate, Paul Kerlinger describes three kinds of migrations: Complete, partial and irruptive.

In complete migration all members of the species have separate breeding and resting grounds, usually far apart. Birds that winter or rest in Central America and breed in Connecticut practice complete migration.

In partial migration, the most familiar and most common form, some members of a species move away from summer breeding grounds while other remain. In our area, some robins and Eastern Bluebirds fly south in the fall while others stick it out during the winter. Partial migration almost always results in overlapping ranges and if you look at a range map in a field guide, you will see a breeding range, a winter range, and a “year-round range.”

Irruptive migration occurs when a species that normally inhabits a region year round decides to burst from its normal territory and invade another. Variations in food and population supplies can cause irruptions of certain birds, particularly those whose normal territory is boreal. For instance, both crossbills and redpolls, finches that inhabit the Canadian forests, may descend into the States in great numbers some winters. These irruptions are related not only to the food supply but the number of birds. Some years, the supplies of cones and the seeds within them are rich, causing the finches to increase in number. Then hard times hit and not enough food is available to supply all the birds, forcing them to look elsewhere.

Among the kinds of birds that may appear in irruptions are northern species of nutcrackers, jays, grosbeaks, woodpeckers, finches, and hawks.

One of the most famous irruptive species in the Northeast is the Snowy Owl. In winters when the lemming population declines in Canada, these large white birds will appear in many northern states. One year in the city of Stamford, a Snowy Owl was discovered perched atop a streetlight in a downtown section. The discoverer was a child, who had never seen such a big, white bird before and who reported to police that he saw a “chicken” on the streetlight.

When winter ends, the irrupting birds from the north head back home.

Seed sale

Bedford Audubon Society is having its annual seed sale, the society’s main fundraiser, which supports managing sanctuaries, conducting avian research, and providing educational programs for the community.

They offer 10 different seed and peanut items and two kinds of suet. To learn more and to order seeds, call Steve Ricker at 914-234-2934. Pick up for the seed sale is on Saturday, Nov. 5 (9 to 3) at Bedford Hills Town Park.

Coming up

Fire Island Hawk Watch, trip with Saw Mill River Audubon, Thursday, Oct. 6, 9 a.m. from Millwood A&P, 914-666-6503 or email This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Guided Bird Walks, Saturdays, Oct. 8 and 15, from 7 to 9 a.m., free, Audubon Greenwich, 613 Riversville Road, meet in the main parking area, 203-869-5272 x239 greenwich.audubon.org

Birding with Luke Tiller: Saturday, Oct. 8: Allen’s Meadow and Secret Hotspots in Wilton, 7:30 a.m.; Saturday, Oct. 29: Sparrow Big, 7:30 a.m.; $10 each; To register visit www.sunrisebirding.com/walks.htm

Breakfast with the Hawks, observe migrating hawks, Thursday, Oct. 13, 9 a.m. free light breakfast, Bedford Audubon, at Arthur Butler Sanctuary, 265 Chestnut Ridge Road, Bedford Corners, register with Adam Zorn at 914-666-8448 or email  This e-mail address is being protected from spambots. You need JavaScript enabled to view it , www.bedfordaudubon.org.

Trans-Pacific Migrations, talk by Peter Pyle of Institute for Bird Populations, Thursday, Oct. 13, 6:30 p.m., $10 adult, $5 kids, Audubon Greenwich, 613 Riversville Road, RSVP 203-869-5272 x239 greenwich.audubon.org

Hook Mountain Hawk Watch, trip to west side of Hudson, Saturday, October 15, 9 to 3, $15, Audubon Greenwich, 613 Riversville Road, RSVP 203-869-5272 x230 greenwich.audubon.org.

Copyright 2011 by Jack Sanders. Send sightings or comments to: jackfsanders [at sign] gmail.com, or to Bird Notes, Box 1019, Ridgefield, CT 06877. 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.