Swallows on the Wing

Swallows move fast and spend most of their waking hours hunting in the air. Their insect prey is invisible to us yet these birds spot it and catch it in flight. As they hurtle, loop and glide overhead swallows seem more like a concept than something with definite features, more like a verb than a noun. Swallows extend the romance of the aerial sphere beyond our knowing.

Three Tree Swallows and a Barn Swallow (top center)

And yet occasionally they alight on an observable perch. With the right light and the aid of binoculars their sleek beauty comes to the eye.

Barn Swallow over the quarry pond

One understands that swallows are able to catch more calories than they expend in their energetic pursuit of prey.

Barn Swallow feeding young

They also have to keep up with the demands of their brood. When fledglings leave the nest they line up around the quarry to observe and practice their difficult trade, while still being provisioned by adults.

This transfer of food usually comes as a bolus, a mouthful comprising many insects rather than one at a time.

Male Tree Swallow

Swallows have adapted to hunting insects on the wing by developing a slender, streamlined body and long, pointed wings, which allow great maneuverability and endurance, as well as frequent periods of gliding. Their body shapes allow for very efficient flight; the metabolic rate of swallows in flight is 49–72% lower than equivalent song birds of the same size.¹

 The impression is falcon-like scaled down to smaller prey.

Juvenile Tree Swallows

In late summer the Halibut Point quarry and shoreline provide good hunting prospects both high and low over water.

Gleaning from the water surface

The juveniles especially are attracted to picking bugs from the surface of the quarry.

Tree Swallow and the blue moon

Not surprisingly, swallows resemble falcons in their visual acuity as well as in their body and flight characteristics. They have a bifoveate retina that provides sharp lateral and frontal vision, an unusually long eye that enhances spatial resolution, a large posterior blind area, and a narrow binocular field.²

Their relatively long eyes allow for an increase in visual acuity without competing with the brain for space inside of the head.¹

Tree Swallows feeding on bayberry berries

In preparation for their fall migration southward swallows pluck extra calories from bayberry bushes along the Halibut Point shoreline.

Migrating swallows en route south

They are among the minority of songbirds that migrate primarily during the daylight hours. Although day migrants are more exposed to avian predators there are some advantages.  Day migrants are able to navigate using land formations they can see easily, such river valleys, coastlines, and mountain ranges. And, unlike night migrants, those that migrate by day can feed as they go. For Tree Swallows this means they can hunt both flying insects and their favorite berries.³  

Swallows form just one branch of the diverse winged world but they seem to have taken the achievement of flight to its ultimate degree.

1. Wikipedia. 

2. "We also show that swallows and diurnal raptors (hawks and falcons) have converged on a similar visual configuration but that, interestingly, predatory songbirds that ambush prey (flycatchers) have not converged on the same suite of traits. Despite the commonly held belief that predators rely on binocular vision, the temporal (frontally projecting) fovea present in swallows—but not present in other songbirds—is likely not involved in binocular vision. Instead, swallows have four nonoverlapping foveae in a 100° arc around the beak, which can improve the tracking of frontally located aerial prey that are engaging in evasive maneuvers."

Tyrrell, Fernández-Juricic and McPeek, "The Hawk-Eyed Songbird: Retinal Morphology, Eye Shape, and Visual Fields of an Aerial Insectivore," The American Naturalist, vol. 189 # 6, June 2017.

3. Treeswallows.com