Olive-sided Flycatcher by John Sill © Massachusetts Audubon Society. Courtesy of the Museum of American Bird Art.
The Olive-sided Flycatcher (Contopus cooperi) is the largest of the Contopus and Empidonax flycatchers with which it might be confused. Its call is a distinctive quick THREE BEERS, and among those of us who appreciate a beer now and again, it is a particularly easy mnemonic to remember. Also distinctive of this species is its habit of perching in the open on dead branches on treetops. Olive-sided Flycatchers have a proportionally large, dark head and stout bill. Their upper parts are a dark, brownish olive. Their throat, breast, and belly are white and stand out against dark flanks that are striped with brownish-olive, giving the appearance of an unbuttoned dark vest. White patches along the side of the rump are distinctive and especially visible in flight. The sexes are similar in plumage.
The history of the taxonomy of the Olive-sided Flycatcher is most interesting. First described as Tyrannus borealis in 1832, it was subsequently placed in the genus Nuttallornis in 1887, and later moved to Contopus in 1983 by the American Ornithologists’ Union. The specific name was changed to mesoleucus in 1931, then back to borealis in 1945, and finally to cooperi in 1998 after it was determined that this name had been used by Thomas Nuttall three months before the name borealis had been published in 1832. The Olive-sided Flycatcher is generally recognized as a monotypic species, although because western birds average slightly larger than eastern birds, as recently as 1997 attempts were made to establish eastern and western subspecies. The general consensus, however, is to retain the species as monotypic with the caveat that the problem needs more study.
Olive-sided Flycatchers breed from western Alaska to Newfoundland in a swath across central Canada extending south through the Great Lakes, northeast New York, and New England, and in a few spots in the Appalachians. They breed along the West Coast from Alaska through much of northern California, in the mountains of southern California, and into Baja California. They also breed throughout much of the Rocky Mountains south to New Mexico and Arizona. They are long-distance migrants, with some wintering in southern Mexico and most in the Andes through Peru to western Bolivia and to a lesser extent east through Amazonian Brazil. In Massachusetts, Olive-sided Flycatchers arrive in late May and migrate through until mid-June. The fall migration is in late August through early September. They are a very uncommon and decreasing local breeder in western Massachusetts, and an uncommon migrant at all seasons.
The Olive-sided Flycatcher is monogamous and raises a single brood. There are some indications that it may be breeding-site faithful. The male’s quick THREE BEERS apparently functions as territorial advertisement and to attract mates. Males may sing at all times of the day. Females sometimes sing but their song is less distinct. The flycatchers give a churring call during aggressive encounters, and twitter when approaching a mate at the nest or on a branch. Male courtship includes display flights and often chasing the female. Males and females may do swooping flights together. Agonistic displays include crest raising, tail pumping, and bill clicking.
The Olive-sided Flycatcher is primarily a bird of mountains and coniferous forests from sea level to mountain timberline, usually in edge habitat and along natural openings such as canyons, rivers, ponds, or bogs, and also at the edge of forest burns and logging remnants. The female chooses the nest site although the male may help in the selection process. The nest is a bulky open cup of twigs, rootlets, and lichens, most often placed on the upper surface of a branch, normally in a conifer, and usually 5–100 feet above the ground. The nest is constructed mostly by the female. Only the female develops a brood patch and she alone incubates the eggs for the two weeks or more until hatching. The usual clutch is three white or buff-colored eggs blotched and spotted purple-gray near the large end. The male may bring food to the female during incubation. The young are altricial: their eyes are closed, they have sparse down, and they are helpless at hatching. The female broods the young for up to three weeks until fledging. Both parents feed the young for a week or more after fledging. The fledglings typically remain in the territory with the adults for two weeks or more. The family may stay together until the fall migration.
Olive-sided Flycatchers primarily forage for insects by hawking or sallying out from high, exposed perches. Although the bulk of their diet consists of wasps and bees, they also take grasshoppers, moths, dragonflies, flies, and just about any other flying insect.
The Olive-sided Flycatcher suffers nest predation by jays, ravens, and squirrels. Both parents attack intruders, including humans, and they will dive bomb them and sometimes even strike them. The history of the Olive-sided Flycatcher in Massachusetts, as in much of the remainder of its range, is a story of decline. In the mid-nineteenth century, it was a widely-distributed breeder throughout the state. By the end of the first quarter of the twentieth century, it had disappeared from most of Massachusetts, breeding only in the boggy areas of Worcester County and the pine barrens of southeastern Massachusetts and Cape Cod. By the end of the twentieth century, it bred in only a few places in Berkshire and Worcester counties. The Breeding Bird Census results for 1966–1996 indicated a roughly 4% decline in most regions of Canada and the United States. Open-habitat breeders, Olive-sided Flycatchers may have suffered from fire suppression, as well as from dips in prey availability and the effects of severe weather fluctuations associated with climate change. Habitat alteration on the wintering grounds is also considered a factor. The U.S. Fish and Wildlife Service lists the Olive-sided Flycatcher as a Species of Concern. We can only hope that the situation brightens for this delightful flycatcher.