the Ash-throated Flycatcher and Its Relatives
The Ash-throated Flycatcher is familiar to any birder in San Diego County. But probably few of us think much about the other 21 species with which the Ash-throat shares the genus Myiarchusa group of maddeningly similar flycatchers common and conspicuous through most of the New World. Mary Beth Stowe's discovery of San Diego County's first known family of Brown-crested or Wied's Flycatchers at the Roadrunner Club in Borrego Springs shook us suddenly out of our complacency and suggested the flycatchers of the genus Myiarchus as a topic for this issue of Wrenderings.
Since the Ash-throated Flycatcher is the only kind of Myiarchus expected in San Diego County, it's essential that we familiarize ourselves with its appearance, behavior, voice, molt, and distribution before considering any other species.
Its size between a phoebe and a kingbird, grayish brown upperparts, pale gray throat and breast, pale yellow belly, and rufous flashes in the wing and tail readily identify the Ash-throatas a member of the genus Myiarchus. Understanding its identification as a species, though, requires attention to finer details. Fortunately, the Ash-throat, like the other members of its genus, has only two plumages. Males and females look identical, plumage wear does not change the birds' appearance grossly, and there no subspecies that need concern us. The Ash-throated Flycatcher's juvenile plumage, though, is poorly addressed, even in the latest field guides.
The belly of the juvenile Ash-throated Flycatcher is a little paler yellow than the adult's, and the flimsier texture of the juvenile's feathers may be evident in a close view. The only conspicuous difference between the adult and juvenile is in the tail pattern. Remember that a bird's tail folds so that the central feathers are on top, then each successive feather toward the outside lies underneath the feather toward the center. So, as you look at a perched bird's folded tail from the back, you see central feathers and maybe just the outer edges of the others; as you look at a bird's folded tail from the front or below, you see just the outer feathers.
In the adult Ash-throated Flycatcher the central tail feathers are totally gray-brown, so from the back the folded tail of the perched bird looks plain brown. The rufous is confined to the inner webs of the rectrices, so we see the adult's rufous clearly only when the bird spreads its tail, as to brake when coming in for a landing. In the juvenile, however, the central rectrices are largely rufous, with just a narrow stripe of dark brown along the feathers' shafts, so from the back the folded tail of the perched bird looks rufous.
On the outer tail feathers of the adult Ash-throated, the rufous on the inner web doesn't extend to the tip of the tail; the brown from the outer web swings inward to cover the whole tip of the feather. On the juvenile, the outer tail feathers are almost completely rufous, with just a hint of brown on the basal half of the inner web. Because of the way the tail folds, the outer feathers are better seen from the front or below, though this often means in poor light. Look at the bird from the back and above when you can. Being able to identify the juvenile Ash-throated Flycatcher will not only help you identify young birds that may still be following their parents, it is critical to distinguishing the Ash-throated from the other species of Myiarchus.
The Ash-throated Flycatcher offers some interesting biology, too. The members of the genus Myiarchus are unique in being the only North American flycatchers that nest in cavities. Ash-throats nest most commonly in old woodpecker holes in trees, but like many other secondary cavity nesters competing for this scarce commodity they must be flexible in their choice of nest sites. The availability of suitable nest cavities is likely a factor limiting the birds' distribution and numbers. The older literature features many reports of Ash-throated Flycatchers taking advantage of man-made nest sites like drain pipes, mail boxes, and a hole in the leg of a pair of overalls hung on a clothesline. Ash-throats are clientele for bird boxes, as Kirsten Winter described in the last Wrenderings. In treeless chaparral at Carrizo Overlook (Q26) I found one carrying nest material to a gate made of heavy iron tubes, and in grassland behind a firing range in Camp Pendleton (C3) I found a pair entering the tailpipe of wrecked vehicle used for target practice.
The major material the Ash-throated Flycatcher uses to line its nest cavity is mammal fur. Knowing this helps us interpret what that amorphous mass the bird is carrying in its bill might be. Watch carefully to avoid confusing a wad of fur with a wad of insects or stray hairs with long insect legs. Another aspect of the Ash-throat's biology worth keeping in mind is that it often nests late in the summerwe have records of its nest building as late as 20 June and fledglings as late as 29 July.
In the Anza-Borrego Desert the Ash-throated Flycatcher shadows the Ladder-backed Woodpecker, using the woodpecker's holes in the stalks of Agave deserti and the trunks of Yucca schidigera. Yet the flycatcher occurs in some desert squares where the woodpecker appears absent. Some of these could be nonbreeding birds or late migrants hanging out through the breeding season in unsuitable habitatwe lack actual nesting confirmations from these squares. Or are the flycatchers in the bleakest parts of the Anza-Borrego finding unconventional nest sites there too? I haven't found any mention in the literature of the Ash-throat using cavities in rocks or bluffs but I suggest it as a possibility. Charles E. Bendire (of thrasher fame) reported two flycatcher nests in old Cactus Wren nests, revealing another opportunity for the Ash-throated Flycatcher to take advantage of woodpecker-free desert. Nevertheless, our results reveal a regioncentering on the Ocotillo Wells off-road vehicle areawhere the Ash-throated Flycatcher is absent.
Along the coast, the Ash-throated Flycatcher exemplifies an interesting pattern, what I call an "anticoastal" distribution. That is, the species is widespread at low elevations but is absent or scarce in squares touching the coast. Note that we have no confirmations of nesting for such squares, in spite of their being among the best covered. I'm unsure of the reason for this anticoastal distribution, but the Ash-throat shares the pattern with a few other species like the Western Kingbird and Lark Sparrow.
The Brown-crested Flycatcher is a rather recent arrival in California, first discovered along the Colorado River in 1921 and occurring in numbers there by 1930. Since then it has colonized a few desert oases farther west, mainly Tecopa, Morongo Valley, the Mojave River, and the South Fork of the Kern River. Its push west was likely inhibited by the decimation of riparian forest along the Colorado shortly after its arrival, then the lack of woodpeckers large enough to excavate cavities large enough for this biggest species of Myiarchus. Thus west of the Colorado the Brown-crested Flycatcher may depend largely on man-made cavitiesthe pair at Covington Park in Morongo Valley nested in the horizontal metal pipe of the swing set. Thus a search for further nesting of the Brown-crested Flycatcher in the Anza-Borrego Desert might focus most profitably on artificial cavities around tall planted trees in Borrego Springs
The Brown-crested Flycatcher's plumage is nearly identical to the Ash-throat's. The pattern of the adult's outer tail feather differs: the rufous of the inner web extends all the way to the tip, the brown of the outer web does not curve around the tip as on the Ash-throat. This feature is very difficult to see in the fieldit's seen well only from the back when the outer rectrix accidentally gets twisted out of its normal position. The juvenile Brown-crested's tail pattern is the same as the juvenile Ash-throated's. The birds' English names are of no help; in both species the throat is ash-gray and the crown brown. In South America the Brown-crested may be the only Myiarchus with a brown crest, but in North America all members of this genus are brown-crested, so the change from the species' previous name, Wied's Crested Flycatcher, was pointless.
As Mary Beth describes, the useful features identifying the Brown-crested Flycatcher are size and voice. The Brown-crested is about 10% larger than the Ash-throated in most dimensions, but its bill is larger by 25%, with a more prominent hook. The Ash-throated's usual call may be rendered something like "prit-wherr"; often it calls simply "prit." The call is easily recognized but isn't especially vigorous. The Brown-crested Flycatchers at Borrego Springs called a raucous "quick!," like a note out the Western Kingbird's song. It sounds like it comes from a bird much bigger than an Ash-throat. When I heard the birds at Borrego Springs, even before I saw them, my first thought was "those are some big flycatchers!"
The Ash-throated Flycatcher is basically a summer visitor to San Diego County, but we have 16 winter records in the past three years. The species' normal winter range is not far from us, extending to northeastern Baja California and eastern Imperial County. I thought our atlas effort might reveal the Ash-throat as a regular winter visitor in parts of the Anza-Borrego Desert, but so far this hasn't happened. Especially in the stands of elephant trees where we discovered the wintering Gray Vireos I thought we might find wintering Ash-throated Flycatchers too. In Sonora, the flycatcher, like the vireo, eats the tree's fruit and disperses its seeds. Just five of the 16 winter records are from the Anza-Borrego Desert; seven others are scattered through the coastal lowland. Most interesting are Frank Unmack's four sightings in February 1999 in three squares (T27, U27, U28) in the Jacumba region, where wintering Ash-throated Flycatchers were previously unknown.
Finally, before we leave the genus Myiarchus and its occurrence in winter, we should remember the Dusky-capped or Olivaceous Flycatcher, known in San Diego County from three records in late winter and early spring. With the Ash-throated so rare in San Diego County in winter you should always consider the possibility of the Dusky-capped whenever you discover a wintering Myiarchus. Its small size, minimal rufous in the tail, and plaintive call make the Dusky-capped more easily distinguished from the Ash-throated than the Brown-crested. The crown is no duskier a brown than in those two speciesagain we've been saddled with a name appropriate for the bird in South America but not in the United States.