What About the Other Bluebirds?
The eastern bluebird has drawn the most attention, but the West's two species have also needed a helping hand
The Crushed and bent feathers on the mountain bluebird's shoulder were, for Art Ayles worth of Ronan, Montana, a revelation. The year was 1982, and the amateur naturalist was deep into a project to aid mountain and western bluebirds. His plan was simple: Put out nest boxes. After all, the same strategy was providing refuge for the eastern bluebird with great success. All three species had been in a serious decline, and all three could presumably benefit from nesting boxes.
To Aylesworth's consternation, even though western bluebirds had taken to the digs okay, few mountain bluebirds had moved in. And now, on this spring morning, a bird flew to one of his nearly 400 boxes, stuck its head in the hole and tried to squeeze inside. When it turned away, its ruffled shoulder told all. "Good grief, the hole's too small," Aylesworth whispered to himself.
That moment ten years ago was one of the more obvious reminders of an oft-overlooked truth about this country's bluebirds: With subtle variations in size, coloration and habitat, the three species are not created equal. Not only that, they don't all share the same level of support from bluebird fanciers. For more than a decade, the eastern bluebird has had at least one apparent advantage over the other two: Most of the 5,000 or so members of the North American Bluebird Society (NABS), formed in 1978, live in the East. So that's largely where these most organized of bluebird fanciers build and put up nest boxes, monitor survival rates and discourage house sparrows and starlings from using the structures.
Of course, you don't have to be a society member to build boxes. And you certainly don't have to be in the East. Back in 1982, when Aylesworth noticed that his box hole didn't comfortably accommodate the mountain bluebird, he designed his own "hole tap" drilling tool to enlarge entrances by a sixteenth of an inch-just large enough to admit bluebirds, small enough to discourage undesirable squatters. He then took a week off from his job as an insurance agent to remodel hundreds of boxes, and shipped the tool to other western bluebirders, urging all to do the same.
Bluebirds are members of the thrush family, kin to robins and native only to North America. Eastern bluebirds occupy the United States and southern Canada east of the Continental Divide. The western and mountain species generally stay west of the Great Plains, from Alaska to Texas. A reddish breast and throat distinguish the eastern male. The western male sports the same red breast but with a bright blue throat. And mountain bluebird males show pale blue or white in place of the red. Females mimic male coloration, but with muted blues that often descend into soft grays. Biologists are at a loss to explain why bluebirds are blue-though, like many other creatures, males' brighter colors help them attract females in breeding competition.
According to the U.S. Fish and Wildlife Service's annual Breeding Bird Survey, eastern bluebird populations have increased by 2.3 percent over the survey's 26 years (the survey tracks trends but not actual population numbers). Mountain bluebird populations remain essentially stable, while western bluebird numbers have declined an average 2.2 percent per year. "If that decline continues much longer, western bluebirds could become rather scarce," says survey coordinator Bruce Peterjohn. Typically, western bluebird numbers rise slightly for several years, suffer a sharp decline, then rise again. Severe weather may help explain this pattern.
Those statistics are weighted with data from California, which could mean there's less of a problem elsewhere. New Mexico and Washington, for example, probably have more western bluebirds now than when the survey began. And last year's overall western bluebird count was up 2.4 percent over 1990.
In many ways, the three bluebird species are quite similar. Biologists recently discovered they occasionally even interbreed. At the heart of the survival saga of all three lies a behavioral idiosyncracy that once threatened to become their fatal flaw. Eons ago, bluebirds learned to avoid predators by laying eggs in arboreal cavities. Other birds did too, but most developed backup plans. Some, like woodpeckers, excavate their own holes. Others build open nests when cavities aren't available. But bluebirds, along with a few other species in the United States (and about two dozen worldwide), use only cavities they themselves cannot create.
Bluebirds once nested mostly in abandoned woodpecker digs and cavities in rotting trees. Then came European settlers. "At first, humans unintentionally helped bluebirds by improving habitat," says Lawrence Zeleny, a retired Maryland biochemist and the nation's foremost bluebird expert. The birds' summer fare consists mostly of easy-to-spot insects plucked off the ground-and pioneers turned portions of forests into insect-rich meadows. Newly rotting stumps where settlers cleared trees provided new nesting cavities, as did the ubiquitous wooden posts that fenced the western range.
Gradually, however, the human influence has harmed more than helped bluebirds. Cattle grazing in western creek bottoms (called riparian areas) have destroyed innumerable potential nesting trees, harming critical habitat for a range of species. A 1990 Environmental Protection Agency report found that field observations from the late 1980s "suggest riparian areas throughout much of the West were in the worst condition in history."
Westerns also thrive in ponderosa pine habitat, which they may favor because the lack of underbrush beneath the water-hoarding trees makes spotting insects easier. Although ponderosas occur naturally on millions of acres in the West, logging reduces that total each year. "And even if more ponderosas are planted, it may be decades before western bluebirds benefit," says Peterjohn. In contrast, mountain bluebirds can thrive while feeding in open areas, possibly because they evolved at high elevations near treeline. They often hover as they search for insect prey-the way their ancestors probably did when trees were scarce. Other bluebirds typically hunt from a perch.
The chain saw's invention in the 1920s made felling dead trees easy, which helped eliminate cavities. More cavities disappeared when steel replaced wooden fence posts on a large scale following World War II. Today, bluebirds lose ever more habitat when expanding farms cut down the shelter belts and woodlots that were once typical of small family farms.
Then there are predators, which sometimes take their prey in front of horrified bluebird fanciers. Homemaker Dorothy Dickson, for one, witnessed a Swain-son's hawk near Red Deer, Alberta, finish off a mountain bluebird feast two years ago. The hawk waited on a telephone pole while a bluebird fledgling--the last in the box--fluttered toward a nearby fence on its maiden flight. Then the raptor grabbed the novice in mid-air. "Apparently the Swainson's picked off each young bird as it emerged from the box,- Dickson says. Hawks are not alone. House cats, raccoons and magpies are all among bluebird predators.
Competitors cause the most trouble. Worst are two rowdy immigrants, house sparrows and European starlings. In 1853, the Brooklyn Institute released a few dozen imported house sparrows into New York's Greenwood Cemetery. The newcomers spread westward, and by 1900 were one of the continent's most common birds. In 1890, New York drug manufacturer
Eugene Scheifflin released 60 European starlings in New York's Central Park. William Shakespeare had mentioned starlings in a play, and Scheifflin wanted America to have all birds referenced by the great bard. By 1940, millions had spread across the country, evicting bluebirds and other native species.
"House sparrows and starlings are so aggressive they usually take over any cavity they can enter," says Zeleny. Sparrows have even been known to build their own nest atop the body of an adult bluebird after killing it. The interlopers claim more than space: Flocks of starlings can strip large areas of critical food.
In the 1940s, observers began noticing a bluebird decline. Though no one made official counts, bluebirds that once outnumbered robins in many places became rather rare. Zeleny estimates that eastern bluebird numbers plummeted by as much as 90 percent between 1936 and 1976, and there is no reason to believe the two western species fared any better. In his 1976 classic book The Bluebird: How You Can Help Its Fight For Survival, Zeleny warned: "It may be but a matter of time before the sighting of a bluebird will be possible only in the remote areas of the country." But for the 1978 formation of NABS, he might have been right. NABS members have put up about 40,000 boxes, and spokesperson Chuck Dupree estimates that nonmembers may have put up 100 times that many.
As for Aylesworth, ten years after he made his hole-enlarging tool, he and other volunteers in tiny Ronan (population 1,600) have built 25,000 boxes for mountain and western bluebirds. Many more of the structures have also gone up across the western landscape-including a 700-mile trail with 4,200 boxes put up in Montana by volunteers in 1989.
In good habitat, mountain and western bluebirds occupy about two-thirds of all well-maintained boxes, with some trails approaching 100 percent occupancy. Sometimes the birds can't wait to get in. Several years ago, Idaho bluebirder Al Perry found a male mountain bluebird sitting atop his car and a female fluttering against the window. In the back seat sat a nest box, with the entrance clearly visible. The two noisily followed Perry as he carried the box to a tree. They moved in immediately.
If enough people put up boxes and monitor them, says Aylesworth, "we should have western and mountain bluebirds forever." And if you already have boxes with entrances too small for mountain bluebirds, call Aylesworth. He'll be glad to lend you his hole tap, still making the rounds in the West.
Gary Turbak writes and observes bluebirds from Missoula, Montana.