Elusive swallows coming to Valley

In early March the first swallows arrive in Yakima from the south. Swallows eat insects, so, you ask, are there really enough bugs out in early March? It turns out there are, especially near water — certainly enough for both tree and violet-green swallows to arrive and go on bug patrol.

These birds are among our earliest returning birds from the tropics, along with flycatchers, vireos, warblers, orioles and tanagers. Hundreds of millions of birds migrate north from their tropical wintering homes to take advantage of the seasonal explosion in insects, seeds and fruits that come with our warmer temperatures of spring and summer in the United States and Canada.

WHERE AND WHEN: Look for swallows fluttering gracefully low over a pond when they first arrive. Evidently, that’s where the most bugs congregate during cool days in early spring. Look for them on the Yakima Greenway ponds or over the Yakima River. As the temperature warms, the swallows fly ever higher. Sometime in April they return to their nesting habitat about marshes, in woodlands along the Yakima River, and into the lower Cascades (as in the Wenas Valley or Nile areas).

Do not expect swallows before mid-April in the mountains, though, as spring arrives later there.

A pair of tree swallows perch atop a post in the Nile area off State Route 410, west of Naches, in May 2006. You can see more of Denny Granstrand’s bird photographs online at www.granstrand.net/gallery. (Photo courtesy DENNY GRANSTRAND)

CHOW TIME: Flying insects make up their entire diet. In cold weather, they may pluck insects from the surface of a pond or even resort to berries in emergencies.

SOCIAL LIFE: Tree swallows nest in holes in trees, stumps and bird houses. The popularity of bluebird box “trails,” like the one built and monitored by volunteers in the Wenas Valley, has also been a great boon to tree swallows, as these two groups of bird like the same type of box in the same habitat.

As this species arrives when nights still regularly fall below freezing, they wait until the weather warms (April in the Yakima Valley, May in the Cascades) to begin nesting. The female does most of the building of the nest, a cup of grass, roots and twigs, lined with feathers in the cavity. The female does almost all the incubation of the four to six eggs, for 14 to 15 days. The hatchlings are fed by both parents for a little over three weeks. Then the youngsters take their first flights.

As the summer progresses into fall, these swallows join others of their kind into flocks, sometimes numbering over 300, and head south. While in spring they hug close to water at low elevations, where the insects are most abundant, in fall many travel south in the mountains, sometimes above the Cascade crest.

Evidently, warm late summer winds drive lots of flying insects (especially winged ants but probably others) to high altitudes, making a mountain migration route an easy way to get a meal.

WHAT YOU MAY NOT KNOW: Mankind’s knowledge of migration took a long time to clarify. Aristotle’s word was law among educated men until late in the Middle Ages. He asserted the reason swallows and many other birds disappeared in fall was they hid themselves in the ground or underwater all winter in marshes. The belief in aquatic swallows persisted as late as the 18th century.

• Wildlife Moment, focusing on native wildlife, typically runs in Outdoors on the first Tuesday of every month, with the cooperation of the Yakima Valley Audubon Society.