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The bird to associate with last week's weather is the hermit thrush.

This thrush is an early migrant. It's not abundant, by any means, but sometimes it occurs in quite large numbers.

That happened last week.

Sunday's snowstorm interrupted the northward passage of these birds, producing what is known as a "fall." The notion is that the birds fall out of the sky. Of course, this is not quite what happens. Rather, low pressure systems that produce snowfall also produce difficult flying conditions, and the birds settle down to wait out the weather.

This happens with species other than hermit thrushes. The occasional fall involving warblers is a highlight of any birder's year, since it offers a chance to observe many species much more closely.

Warbler falls occur later in the year, because most warbler species migrate in May. Wet, foggy weather interrupts their journeys northward.

As April migrants, on the other hand, hermit thrushes encounter snow, which fell last Sunday and persisted through the week.

This brought hermit thrushes down in unusual numbers.

Most often, these birds occur as individuals, and every spring produces a few sightings. Reports last week were of groups of birds, and this is unusual.

'Bird of passage'

The hermit thrush is a "bird of passage" here. Migrating thrushes are bound for the scrub forests of Canada. The Grand Forks County bird list ranks them as "fairly common" in spring, occasional in fall migration.

In "Birds of Minnesota," Robert Janssen says the hermit thrush is "a common spring and fall migrant throughout the state. Locally abundant only at peak migration periods. Usually encountered as individuals, but loose aggregations of up to 20 birds can be found at peak periods."

In "Birds of Manitoba," the Manitoba Naturalists' Society explains, "preferred habitat is jack pine forest on either sandy or rocky ridges, including young growth following forest fires, but they also occur in spruce-tamarack bogs and some deciduous woods."

North Dakota doesn't provide this kind of habitat. Minnesota does, however. Janssen reports hermit thrushes have been found nesting as close to Grand Forks as eastern Marshall and Roseau counties.

The hermit thrush is known as a superb singer. "The flute-like, whistling of the hermit thrush is among the most beautiful of all North American bird song, a source of inspiration to birders and musicians alike."

The hermit thrush is a relative of the robin, as even a quick glance will tell. The overall appearance is similar, and so are behavior and some details of plumage-a white circle around the eye, for example-and a kind of drooping of the wings.

Like the robin, the hermit thrush is often found on the ground and it hops like a robin.

The hermit thrush is smaller than a robin, however, and its coloration is quite different-though the pattern is somewhat similar.

The distinguishing characteristic is a bright rusty tail, which the thrush flicks frequently. There is also rust in the wings. Overall, though, the bird appears rather plain, with a brown back that's just slightly lighter on the head. The breast and belly are heavily spotted.

Other thrushes

Two other, similar thrushes occur here in migration, the wood thrush, the gray-cheeked thrush and the Swainson's thrush. These are remarkably alike, but none has the brightly colored tail of the hermit thrush. All are later migrants than the hermit thrush, as well, and timing helps identify the hermit thrush. The earlier the thrush, the more likely it is a hermit thrush.

Wood thrushes, also celebrated singers, sometimes occur in North Dakota, but they are much less frequent.

It may be that Swainson's and gray-cheeked thrushes are as common as hermit thrushes, but they are much less likely to be seen and still less likely to be identified.

The hermit thrush was hardly alone in last week's fall of spring migrants. The early sparrow sparrows were here in large numbers, including white-crowned and white-throated sparrows. The coming days likely will bring a parade of sparrows through our area.