by Frank Keim
Although I’ve never seen an Olive-sided flycatcher in the YK Delta, I have been assured they nest there – probably more in the semi-open boreal coniferous forests with bogs and muskeg in the Kuskokwim region because there is more favorable habitat for them in that area. They also like recent forest fire burns because of the insect foraging opportunities available there. However, since their populations have in recent years declined more than 80 percent, you might have difficulty spotting them today.
If you do encounter one, though, you will first hear the male’s telltale whistle, quick, three cheers, or look, three beers. Also listen for the male’s distinctive quick pip-pip-pip call notes. The bird’s barrel-chested shape, big head, thick bill, and grayish waistcoat also help identify this largest of what many call pewees.
During their hunt for aerial insects like flying ants, dragonflies, wasps, flies, and grasshoppers, these flycatchers perch atop high exposed limbs of a dead or dying tree, darting out to catch their prey on the wing when they spot them, then returning to the snag to consume them.
When they return from their distant wintering grounds mostly in tropical South America, the male finds a good perch on just the right snag, and begins singing his quick, three cheers to both attract a female and let any rivals know who’s in charge in what will turn out to be his nesting ground if he can entice a mate to join him. The male is highly territorial and often has quite a large nesting territory, sometimes in excess of 100 acres, although it usually does not abut his nearest neighbor.
During courtship behavior the male actively chases an interested female through the treetops and he may perform a short display flight to entice her further, which the female may join. Any rival male will be driven out of the territory in a swift aerial chase. Once he has been expelled, the pair reunites, raising crest feathers, clicking bills and bobbing tails and bodies. The pair bond that results is strong, and in one case it was found to be so solid that the pair nested again and again during consecutive years.
These flycatchers are late nesters because of the long distance they have to migrate back to their nesting ground in Alaska, so courtship rituals do not last long. After choosing her partner, the female settles down to finding a nest site usually on the horizontal branch of a spruce tree well out from the trunk anywhere from 5-70 feet above the ground. She then builds the nest in the form of a bulky small cup with a base of twigs and rootlets and a lining of finer materials such as grasses, lichens and needles. The male and female aggressively defend their nesting territory, so much so that once they were seen knocking a hungry red squirrel off the limb where their nest was located.
She lays 3-4 pinkish buff, brown-spotted eggs, and she alone incubates them. 14-19 days later the young emerge naked and helpless, and both parents then take their turns feeding the chicks. 21-23 days after that the hatchlings become fledglings and leave home. After fattening up they join their parents in August and head back to South America. Of all the flycatcher species that breed in the U.S., the Olive-sided flycatcher has the longest migration, with some flying from central Alaska to tropical Bolivia, a distance of 7,000 miles. Once there, both males and females hold and defend feeding territories from others of their own species.
Something I found interesting about this flycatcher is that it doesn’t learn its song. It is genetically programmed and does not change. So there are not any true dialects. All flycatcher species inherit their songs this way, although each species has a different song from all of the others.
The 80% decline in population of this species since 1970 is due in large part to the exponential human destruction of their winter habitat in tropical South America. In recent years, the huge decrease in insect populations in North America due to the misuse of chemicals is also contributing to the decline in their numbers.
I have not run across a Yup’ik name for this species, perhaps because it is found only on the eastern border of its summer nesting habitat in the Kuskokwim region of the YK Delta. Since Olive-sided flycatchers live most of their lives in South America, however, they are bilingual and are called Pibí Boreal in Spanish. And since part of northern South America (French Guyana) is French, they also have a French name, Moucherolle à côtés olive.
The first part of their scientific name, Contopus, comes from the Greek kontos, meaning short, and pous, meaning foot – referring to the relatively short legs of the flycatchers in this genus. The species name, cooperi, was bestowed in 1828 by Charles Lucien Bonaparte, in honor of his friend and fellow ornithologist, William Cooper.