Whenever I walk quietly along the Swallow Hollow boardwalk about a hundred yards south of the trail entrance, I listen for weak spishing sounds coming from high in the cottonwoods that shade the walkway. Francis Weston describes these notes as “scarcely louder than a whisper.” My aged ears have trouble picking them out; only when I listen carefully can I hear the spee spee calls. I am delighted when I do hear them, because they identify the pair of blue-gray gnatcatchers that spend their summers high in these trees.
Now I focus my binoculars on the pair dashing about, some thirty feet overhead. Dashing about indeed, for it is difficult to follow them they are so active. To me they appear like miniature mockingbirds. They have the same light gray plumage and flash similar white outer tail feathers; all they lack is the mockingbird’s flashy white wing patch.
To gain a sense of what a lightweight the blue-gray gnatcatcher is, consider those tiny pats of butter you are served in restaurants. This bird weighs in at about as much as one and a half of those pats. Our only still lighter species is the ruby-throated hummingbird, which weighs only half as much.
Gnatcatchers are great fun to watch. Weston, who wrote the Bent Life History of this species, tells us, “The gnatcatcher is a little bird of intense activity; active, not with the methodical continuity of the brown creeper, but with an irrepressible vivacity of its own in all phases of its life cycle — feeding, nesting, care of its young — at all times, in fact, except during the enforced inertia of incubation.”
Like chickadees, nuthatches, kinglets and creepers, gnatcatchers feed on the tiny insects they find in their constant search of tree limbs and leaves. But gnatcatchers don’t deviate from this diet. Those other species will take seeds from your feeders; the gnatcatchers stick exclusively to arthropods; thus they are very beneficial birds.
Although gnatcatchers do not overwinter here, they appear among the early passerine migrants each year, arriving in mid-April. After a week or two of courtship each pair sets out to build a new nest. I say new because, if there is one left over from the previous year, they won’t use it but will instead tear it apart and use the materials for this year’s home.
I’ve only seen one gnatcatcher nest and it certainly impressed me. It was an only slightly larger version of a hummingbird nest. Form a loop with your index finger against the end of your thumb and you will have enclosed its approximate area.
Located on top of a horizontal limb about 20 feet high, it was beautifully constructed: gray, cup-shaped and compact. Weston informs us that the materials include plant down and fiber, lichens, oak catkins, feathers and bark. All of these ingredients are held together by spider web and insect silk, like that of the tent caterpillar.
Gnatcatchers’ 4-5 eggs are scarcely larger than peas. They are pale blue with reddish-brown spots. Unfortunately, this species is far too often victimized by cowbirds. One observer found over five-sixths of their nests stuffed with cowbird eggs or young. The results are inevitable: tiny gnatcatchers feeding greedy immature cowbirds more than twice their size, their own offspring unable to compete. This may be the major reason why gnatcatchers are so uncommon.