The ranges of birds: What factors change them?

Written by Jack Sanders
Thursday, 28 August 2008 10:54

When I was a kid in Danbury in the 1950s, we hardly ever saw cardinals. Now they are among the most commonly seen local birds. The cardinal’s “range” has definitely changed.

Only 33 bird species were believed to be year-round residents of central New England in the year 1900. By the 1980s, 70 species were resident and by the turn of the 21st Century, still others had established themselves year-round, including the Carolina Wren, Song Sparrow, Red-bellied Woodpecker, and Northern Mockingbird. Among the most recent arrivals is the Black Vulture, a species abundant in the South, which in the late 1990s began making its way into southern New England and New York, where it is now resident.  

Happenings natural and not so natural contribute to the expansion and contraction of bird ranges.  Chief among the factors are changes in climate, accidents of nature, and the hand of man.

North America has been gradually getting warmer and quite a few birds formerly considered “southern” have been making their way into the North for decades as noted above.

One of the most astonishing expansions of range is probably due to an accident. The Cattle Egret is an African species that lives commensally with mammals like elephants and antelopes, whose feet stir up insects egrets eat. In 1880, a flock of egrets crossed the South Atlantic, possibly disoriented by a storm and making use of equatorial wind currents. They landed in South America and their descendants began a march across the New World. They hopscotched Caribbean Islands, arrived in Florida by 1942 and were breeding by the 1950s. Today, the Cattle Egret can be found in every state and province in North America. Instead of elephants and buffalos, it often hangs out here with diary cows.

The vagaries of weather can also reduce ranges, though usually only temporarily. The Carolina Wren finds food mostly on or very near the ground. A heavy and prolonged snowfall can bury their food sources. Sudden, heavy snow may trap others in their shelters, which are near the ground. During the winter of 1995-96, when some 110 inches of snow fell in southwestern Connecticut, the Carolina Wren population appeared to have been wiped out and it took nearly a year before we started seeing wren pairs again. A long period of cold rain in June 1903 killed or drove away many Purple Martins in a huge area from southern Vermont and New Hampshire south to northern New Jersey. Populations did not return to this region for years.

People have extended the ranges of several birds. Monk Parakeets, native to the plains of southern South America, were imported as pets in the 1960s and early 1970s. Some escaped or were let free. These bright green birds have taken up permanent and expanding residence along Connecticut’s coast with Long Island Sound. Gatherings of more than a hundred birds are not uncommon, and their large communal stick houses can be seen in trees in coastal towns.

House Finches, native to the southwestern United States, are now found throughout the East, reportedly because a pet dealer turned loose an illegal shipment of them on Long Island in 1940.  

The most spectacular human introduction was the House Sparrow, a native of Europe. One hundred birds were released in New York City’s Central Park in the 1850s and the species has since spread to every state and province in North America.

Humans have expanded the range of some birds without knowing it. The Purple Sandpiper was once limited to the North Atlantic where they ate the kinds of marine life found on the rocky shores of Labrador, Nova Scotia and Maine. As the East Coast became more developed, more stone breakwaters were built to protect the shoreline, providing habitats for the kinds of food the Purple Sandpiper eats. So a species once limited to a few northern provinces and states may now be found as far south as Florida.

Ranges can get smaller, too, sometimes due to climatic changes but often due to human beings, who change the face of the landscape by felling forests, draining swamps, and developing the land. A dramatic example is the Whooping Crane. When Europeans arrived in North America, they found thousands of Whooping Cranes in what are now 35 states, six Canadian provinces and Mexico. By the 1860s, fewer than 1,400 were left on the whole continent. By 1941, the number was down to 13 birds. Intense recovery efforts have kept the species alive and, slowly, growing. As of April 2008, 377 Whooping Cranes were known in the wild, plus 146 more in captivity. Almost all of the wild ones winter in the Aransas National Wildlife Refuge, 47,000 acres on the eastern coast of Texas, and summer in northern Canada. The shy, reclusive birds could not deal with the settlers who drained swamps and turned the prairies where they nested into farmland. They were also hunted — more than 250 were killed in 1924 alone.

Coming Up

“Return to the Lost World,” Adventures with Birds of Paradise and Tree Kangaroos in New Guinea, with Dr. Bruce Beehler, Wednesday, Sept. 10, 7:30 p.m., free, Bedford Audubon, at Katonah Village Library, 26 Bedford Road, Katonah, This e-mail address is being protected from spambots. You need JavaScript enabled to view it ,  914-232-1999,  bedfordaudubon.org

HawkWatch Weekend Festival, bird-themed workshops, walks, games, shows, raptor counting, ‘green’ vendors, and much more, Sept. 13 and 14,  Audubon Greenwich and Quaker Ridge Bird Club, 613 Riversville Road, Greenwich, 203-869-5272 x239.

Bird Watching Cruises on Long Island Sound and Norwalk Harbor, with Larry Flynn, wildlife conservationist, Saturdays from 7:30 to 10:30, aboard 40 passenger ferry, $20, Norwalk Seaport Association, from Seaport dock, Water Street, 203-838-9444, www.seaport.org.

Bird walks with Luke Tiller, mostly Saturdays at 8 a.m., $10 each; to register, www. sunrisebirding. com/ walks.htm;  203-981-9924, luke.tiller @ gmail.com.

First Sundays, birding at Greenwich Point with Meredith Sampson of Wild Wings, and other guides, meet at the second concession stand, 203-637-9822.

Copyright (c) 2008 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.