Birding by ear is not one of my strengths. Every spring I have to learn to distinguish the songs of the American robin, black-headed grosbeak, and western tanager all over again. I have always envied people who can hear one hear one passing chirp and announce, confidently: “Pine grosbeak!”
There’s one vocalization I have no trouble with, though: the enthusiastic “Quick, three beers!” of the olive-sided flycatcher. Others hear it as “Now see here!” It’s delivered from the tip of a tall conifer, often a leafless snag, which is also a vantage point for scanning for prey. “Bee-catcher” would be more accurate: one study found 83 percent of the olive-sided’s diet to consist of bees and wasps.
These flycatchers are summer residents in our region, wintering in Panama and the Andes and returning in late April or May. They’re easy to detect in the East Bay hills (Tilden and Sibley Regional Parks, Strawberry Canyon), but I’ve also heard them calling for another round in Live Oak Park. Despite their preference for conifers, olive-sided flycatchers have taken advantage of eucalyptus plantings in the Bay Area to expand their local range.
For several reasons, this flycatcher appears to be in trouble. The California Department of Fish and Game lists it as a Bird Species of Special Concern. Breeding Bird Survey data show a consistent decline of about 4 percent per year in California populations from 1968 through 2004. The California Foothills region alone experienced a 5.2 percent annual decline. Similar trends held throughout the bird’s range west of the Rockies, where the core of its population spends the summer. There was a comparable decrease in spring and fall migrants at Southeast Farallon Island over roughly the same period.
The olive-sided and its close relatives, the wood-pewees, have the lowest reproductive rate of any North American passerine (songbird) genus. A typical female olive-sided lays only three eggs per clutch, the young take five weeks to fledge, and only about half of nesting attempts produce fledged young. So the species doesn’t have much of a demographic cushion if habitat changes begin to affect reproductive success.
Olive-sided flycatchers prefer patchy, fragmented forest habitats: edges, openings, and clearings, including clearcuts and burned areas, with less than 40 percent canopy cover. This has to do with their foraging habits: they need unobstructed airspace around their preferred snags.
Forest management practices have had mixed effects on this bird. Some authors have speculated that the flycatcher has historically depended on post-fire habitat. Fire suppression in coniferous forest that eliminates gaps and edges and allows canopies to close will reduce prime olive-sided habitat.
If habitat structure is the key, you’d expect olive-sideds to respond positively to logging. Some do, some don’t. There are studies indicating they do well in logged areas only if enough snags have been retained. By the same token, post-fire salvage logging would also decrease habitat value.
It’s even been suggested, and supported by preliminary data from Oregon, that logged-over areas function as ecological traps for these birds. They look right, so the flycatchers move in; but essential habitat elements-song perches, food sources, whatever-- are missing. Nest predators like squirrels and corvids (jays, crows, ravens) may be more abundant in logged landscapes than in burned areas. For a species operating on a narrow margin already, anything that depresses reproductive success could be critical.
The wild card, as with many neotropical migrant birds, is what’s happening in the winter range. Are the olive-sided’s Andean wintering grounds being converted to coca plantations? It’s known that there has been extensive habitat loss, and that other species that winter in that area, like the cerulean warbler of the East, are declining. What is not clear is how nesting-ground and wintering-ground pressures interact. In other neotropical migrants, the quality of wintering habitat has been found to predict breeding success the following spring.
It’s tempting to focus on breeding habitat for a bird like this just because of the element of control. But I can see managing for the olive-sided flycatcher, if it should come to that, as a real challenge. If a species requires disturbance to create optimum conditions (but only the right kind of disturbance), how do you provide that disturbance? How do you sell controlled burning for the sake of flycatcher habitat? How do you persuade the timber industry to leave those snags?
The dilemma isn’t unique to the olive-sided flycatcher by any means. People working to restore riparian habitat in California have learned that some bird species do best at certain post-flood successional stages. Flood control prevents flood events from resetting the clock. If the birds need the disturbance, how do you simulate it?
The more we learn about ecosystem dynamics, and the roles of fire and flood as renewing forces, the more complex the process of tinkering with the environment becomes.