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Olive-sided Flycatcher: Peregrine of the Flycatchers

Olive-sided Flycatcher by Brian Sullivan, Team eBird
Olive-sided Flycatcher by Brian Sullivan, Team eBird

Called the “Peregrine of the flycatchers,” the Olive-sided Flycatcher migrates through Pennsylvania and formerly nested in the state’s mountains. This large flycatcher is well-known for its loud whistled call often rendered as “Quick, three beers!” that is given from high on a snag or limb at the forest edge. The large boreal pewee has the longest migration of any North American flycatcher with some traveling as far south as Bolivia to spend the winter. It is listed as a Watch List species by IUCN as Near-Threatened because of its declining population.  Olive-sided Flycatchers are now migrating through the state on their way south. This species was just featured as an American Bird Conservancy Bird of the Week. It is one of the high elevation nesting species of the Appalachian Mountains that are in decline.

Here is a summary of its status in Pennsylvania. 

Olive-sided Flycatcher, Contopus cooperi

CURRENT STATUS: Pennsylvania, extirpated as a breeding bird, uncommon as a passage migrant, protected under the Pennsylvania Game and Wildlife Code and under the U.S. Migratory Bird Treaty Act of 1918.

REASONS FOR BEING LISTED: Presently extirpated as a breeding bird, but regular migrant in the state.  Listed as a U.S. Fish and Wildlife Service Migratory Bird of Conservation Concern in the Northeast; Classified as Near Threatened by the IUCN.  It also is a priority conservation species for the Appalachian Mountain Joint Venture.  Loss of habitat in the wintering grounds and declines in conifer forests are among the reasons thought to be responsible for decline.  The loss of bees, wasps, and other pollinating insects that are common prey of this species also may  be a factor.  

POPULATION TREND: Across its range, the Olive-sided Flycatcher has experienced a significant 74 percent decrease from 1966 to 2005 which converts to about 3.5 percent decrease per year. It has declined to the extreme in Pennsylvania because it has not been documented nesting here since the 1930’s, so it is considered extirpated as a breeding species in the state. It once was fairly widespread in the higher elevation forests and wetlands of Pennsylvania. This flycatcher is a regular migrant in spring and fall throughout the state. 

IDENTIFICATION: The Olive-sided Flycatcher is a big boreal pewee that is larger (18-20 cm. length) and bulkier (32 – 37 grams) than the more common Eastern Wood-Pewee (C. virens, 15 cm. in length, 14 grams). Among the dull-colored flycatchers, it has a distinctive appearance with a tapered profile, looking bull-headed, long-winged, and short-tailed. The plumage is brownish-olive with a dull white throat and belly that are framed by dark flanks, making it seem as if is wearing a dark vest over a white shirt. When relaxed, birds show small white silky tufts poking out from beneath its wings. One of the best field marks is its loud ringing whistled song (quick-THREE-BEERS!) that is a characteristic sound of the boreal conifer forest. In migration they nervously call “pip-pip-pip” from their perch. Where they nest, Olive-sided Flycatchers are very persistent singers that often are the first bird heard in the morning and the last one heard at night.

BIOLOGY-NATURAL HISTORY: Described as “the Peregrine of flycatchers,” the Olive-sided Flycatcher has a commanding presence and a stereotypic way of attacking prey from a prominent perch like the larger falcon.  According to Dr. George Miksch Sutton, former state ornithologist, the Olive-sided often perches prominently from “the topmost twig” where it sits in a “dignified, upright manner.” From this prominent perch, it sallies out to snatch its prey mid-air and returns to its perch. They primarily forage in the forest canopy on a variety of flying insects.  It is among the few birds that regularly catch and consume members of the wasp and bee family (Hymenoptera).  Decreases in the numbers of bees and wasps may be a factor in its decline.  The Olive-sided Flycatcher is one of the feistiest and most tyrannical of the Tyrannidae (American flycatcher family).  They are particularly intolerant of raptors or any potential nest predators such as a squirrels, jays, or crows. 

The feistiness of the Olive-sided Flycatcher continues in migration when they often call loudly from tree branches and chase other birds including hawks away from their favorite perches.  Spring migration may begin in Pennsylvania in the first week of May, but more regular in late May and early June.  The long-winged Olive-sided Flycatcher migrates long distances from its northern breeding ground to its wintering ground in southern Central American and northwestern South America.  Most of these birds spend the winter in the northern Andes Mountains.  It has the longest migration of any tyrant flycatcher.  It is one of the latest birds to migrate in the spring with most moving through the state in late May and early June.  Some may be migrating in mid-June, lingering in good habitat for nesting.  Olive-sided Flycatchers migrate late in the spring and into early summer, so nesting season begins later than most species, many still migrating in early to mid-June (McWilliams and Brauning 2000).  They have been observed as early as the first week of May, but most migrate through the state later in May and some straggle through the state in the first and second weeks of June.  Fall migration starts early with some observed in the last week of July, but more likely to be observed in the last week of August and September.  A few can travel through as late as early October.  Migrants are most frequently observed at ridge-top hawk-watching sites.  At one time, fairly large flocks could be observed in migration in Pymatuning, but now most observations are of single birds.  

Like most tyrant flycatchers, the Olive-sided Flycatcher is monogamous.  For a bird of its size, pairs occupy a large territory —- up to 40 to 45 hectares (100 – 111 acres) and generally around 25 – 50 acres.  Females arrive on the nesting ground later than males and tend to forage closer to the nest than their mates. The female primarily, if not exclusively builds a loosely-formed, cup-shaped nest generally out on a limb of a conifer tree, far off the ground.  The nests are generally well-hidden in a cluster of live needles and twigs.  Pairs nest only once but will renest if the first attempt fails.  The female usually lays three eggs, but sometimes two, four, or five.  The pair divides up the parental duties.  Only the female broods the nestlings, but the males help feed the nestlings and fledglings.  Both incubation and nestling period last 15 – 19 days, but  some observers have recorded 16 days.  Nesting period may vary according to local temperatures that can be variable in the far north or at high elevations.  The young apparently depend on the adults for food for about a week after leaving the nest.  Its rigorous nest defense is certainly helpful to avoid cowbird parasitism that affects other forest songbirds. 

PREFERRED HABITAT:  Many Olive-sided Flycatchers migrate through Pennsylvania on their way to their wintering grounds in the fall and on the way to their northern breeding grounds in the spring.  They often perch prominently from a branch or snag at the edge of the woods or in a fence row, sometimes at the edge of a pond or cutting.  In spring, they can call loudly with their whistled song or call notes. 

When it nested in the state, the Olive-sided Flycatcher was found in higher elevation forests and wetlands usually over 1500 feet.  A characteristic member of the North American boreal conifer forest bird community, it is most strongly associated with the northern conifer forests that extend into Pennsylvania and down the Appalachian Mountains at higher elevations.  Its loud song was commonly heard in summer in places like Pymatuning Swamp, North Mountain, the Pocono Mountains, and what is now known as Allegheny National Forest.  Olive-sided Flycatchers nest in both mature forests and forest edge or burned over areas.  They are often found in bogs, semi-open forest, and the edges of wetlands, ponds, and forest.  Territories invariably include conifers such as spruces, tamaracks, hemlocks, and firs, but also includes deciduous trees such as maples aspens, and mountain-ash.  The first documented nesting in the state was near Hazelton, Luzerne County, in an area that has been converted from forest to strip mines.  The last time it was documented nesting in Pennsylvania was in 1932 when it was found in Pymatuning Swamp, a location that now is under water in Pymatuning Lake.

In recent decades there have been scattered reports of Olive-sided Flycatchers at various locations during the summer, but no confirmed nesting.  Recent summer observations of singing Olive-sided Flycatchers include a tornado a blow-down in an old growth forest, burned over mountain forests, black spruce swamps and pond edges.  The recently occupied locations are consistent with the former breeding range in the state including Pike, Lackawanna, Wyoming, Tioga, McKean, and Warren counties.  A particularly intriguing report of a territorial Olive-sided Flycatcher came from the old growth hemlock – beech forest in Tionesta Scenic Area of Allegheny National Forest in 1993.  The mature forest was more open than usual because of the damage done by a storm and by the defoliation caused by a caterpillar outbreak.  The loss of conifers in some areas has been linked to declines in population in parts of its range, but there seems to be adequate habitat in Pennsylvania for some nesting to occur.  The closest locations where this species has nested recently are within 100 miles (160 km) of the state boundary in the Catskill Mountains.  It also nests in New York’s Adirondack Mountains and Tug Hill region and formerly in the Taconic Mountains.  The Olive-sided Flycatcher has declined in New York in recent decades.  Like Pennsylvania, there is unoccupied habitat in New York leading us to believe that some of the greatest challenges for this species are on its wintering grounds. 

Our migratory birds connect us with others, so here are some of the connections that the Olive-sided Flycatcher makes for Pennsylvania:

For more information about the American Bird Conservancy’s Bird of the Week designation, see: http://www.abcbirds.org/newsandreports/botw/olive_sided_flycatcher.html

For more information about the boreal forest birds of Pennsylvania, see a paper published on the subject that is part of the Proceedings from the conference on the ecology and management of high-elevation forests in the central and southern Appalachian Mountains (starting on page 48):  http://treesearch.fs.fed.us/pubs/36047

For more information about the Appalachian Mountain Joint Venture that features this species as a priority for conservation: www.amjv.org

For more information about issues concerning boreal birds, see: http://www.borealbirds.org

By Doug Gross, PA Game Commission

Thanks to Brian Sullivan of Team eBird for the photograph

Sources:

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