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Always in season: Bird world delivers another surprise

Memorial Day's scarlet tanager was a surprise. I didn't see the actual bird, but only its picture. Not that I hadn't been watching for scarlet tanagers—and even trying to attract them.

But it was the neighbor just north of me the tanager favored this spring. That would put him north and west of Grand Forks about 30 miles as the crow—or the tanager—flies.

The scarlet tanager is a brilliant bird, perhaps the most striking species of bird that occurs in our area. It is a combination of brilliant red on the head, back and breast, with black wings and tail.

It is by no means common here. The Grand Forks County Checklist ranks it as rare, but seen most years. Robert E. Stewart in "Breeding Birds of North Dakota" called the scarlet tanager "fairly common" in Pembina County and in the sand hills of southeastern North Dakota, but uncommon and of only local occurrence in most other sections of the state.

Its preferred nesting habitat is "rich mature forests that occur on slopes of prominent hills and valley bluffs and on well drained floodplains of large streams." Such areas as these are not abundant in the Red River Valley—but they do occur on the valley's rim in both North Dakota and Minnesota. That's where our place west of Gilby, N.D., is located, and that's why I keep my eyes open for scarlet tanagers.

Driven by weather

They come to me in extremis, though, it seems to me. Cold, wet and windy weather forces them down, and they come to sunflower seed that I spread on my driveway. Lots of birds appreciate this gesture, and I regularly draw American goldfinches and several varieties of sparrows, as well as blackbirds and grackles, of course.

Scarlet tanagers are mostly insect eaters, however, and they come to the seeds because insect larvae are not available on wet, chilly days in early spring. The seeds are emergency rations, in other words.

Of course a tanager stands out.

This isn't the case with nesting tanagers. Their behavior is ordinarily "secretive and unobtrusive" according to the monograph on the species in The Birds of North America series published by the American Ornithologists' Union.

Memorable sighting

I've only once seen a tanager at home in its habitat, and that was from the back of a canoe at Lake Bronson State Park in northwest Minnesota, another place on the edge of the Red River Valley. The bird gave Suezette and me such a good look that she was able to correct my drawing of the bird.

Our area is pretty close to the northern edge of the tanager's range. There are reports from central Manitoba, but in general, the northern boundary of tanager country is right along the international border. In general, scarlet tanagers don't occur much farther west, though there are records from the Missouri River Valley. The southern edge of their nesting range is from the southern border of North Carolina into eastern Oklahoma.

The AOU monograph says that surveys of breeding birds show the population of scarlet tanagers has been "relatively stable" since 1966. This is good news, since the tanager faces habitat loss both in North America and on its winter range in western South America.

Tanager numbers have been studied by ecologists interested in what is called "source and sink populations." In this phrase, the source is high quality habitat that produces surplus birds—more than the habitat can support. This is critical to tanagers, which are aggressively territorial in breeding season.

Birds without prime territory occupy sites where the habitat is not so good. These are the "sinks" of the ecologists' phrasing. As long as the source habitat is prime, it can produce enough birds to keep the sink habitat populated.

This may be the case with scarlet tanagers. The monograph says, "In landscapes where the forest is highly fragmented, the species appears to exist as a dynamic mosaic of source and sink populations."

"Highly fragmented" seems to describe forest habitat in our part of the world, although trees are certainly more numerous now than they were in settlement times. A shelterbelt doesn't provide quite the range of niche habitats that a mature deciduous forest offers, though, and I wouldn't expect to find tanagers there.

But a surprise is always welcome in the bird world.