Published July 12, 2009, 01:09 AM

ALWAYS IN SEASON: Swallows mount aggressive defense of their space

Barn swallows have nested on two separate buildings, and they seem to be competing for air space. They’ve certainly become more determined to guard their own territories. Both broods have hatched, but the young are still confined to nests. Perhaps, that explains the adult birds’ aggressive behavior toward passing birds, cats and people. We have a third pair of swallows. These are cliff swallows who have built on to a nest that still another pair of barn swallows abandoned earlier in the season.

By: Mike Jacobs, Grand Forks Herald

The skies around our place west of Gilby, N.D., have turned decidedly unfriendly.

It’s the swallows.

Barn swallows have nested on two separate buildings, and they seem to be competing for air space.

They’ve certainly become more determined to guard their own territories.

Both broods have hatched, but the young are still confined to nests. Perhaps, that explains the adult birds’ aggressive behavior toward passing birds, cats and people.

We have a third pair of swallows. These are cliff swallows who have built on to a nest that still another pair of barn swallows abandoned earlier in the season.

Barn swallows frequently nest inside structures, of course, and their fondness for barns gives them their name.

Our swallows have fastened their cup-shaped nests to the sides of buildings just under the roof overhang. In both cases, they used the frame of a door as support.

The cliff swallows added mud to the barn swallow nesting, completely closing the space between the top of the nest and the roof. They left an opening only large enough for a single bird to pass in and out.

This is the second time cliff swallows have nested on our garage. The first attempt two years ago failed when a cat leaped into the nest from the hood of our car.

We’ve begun parking the car farther from the garage door.

All swallows are colonial to some degree, preferring to nest within short distances of each other.

Cliff swallows are among the most colonial of North American birds, often forming huge colonies of thousands of nesting pair.

So, the single pair on our garage is unusual.

Probably they are pioneers. Each year, some birds depart cliff swallow colonies in search of other places to nest. They scout our property about the middle of June each year.

It may be that cliff swallows are the most abundant birds in the Red River Valley. They commonly nest under bridges, including those over the Red River.

I’ve seen colonies in abandoned farm sheds and on the sides of buildings, too.

Cliff swallows and barn swallows are superficially alike, both with dark blue or purple on the back and salmon or cream on the face and breast. Males are usually brighter than females.

But the shape of the tail separates the two species. Barn swallows have deeply forked tails while cliff swallow tails are square. Barn swallows are a bit larger, too, but the size difference is exaggerated by the length of the tail feathers.

Tail feathers are important to barn swallows aerodynamically — and for another reason.

You guessed it. Females prefer males with longer tail feathers.

These two are among six species of swallows commonly seen in our area.

Tree swallows are iridescent blue or green above and snow white below. They are often encountered in lake country, and they are abundant at Devils Lake, where they nest in cavities in trees that have died in the flood there.

Bank swallows nest in riverbanks. They’re often seen along the Red River and smaller streams. This is a plain bird, a dirty gray in color with a smudge on the breast.

Rough-winged swallows are the least likely to be seen, partly because they are the most solitary of the swallow species. They are rather drably colored, too, but a close look shows some chestnut in their plumage.

The sixth of our swallows is the purple martin. This is the largest of the swallows. Again, the name is descriptive. They will nest in house, but they are finicky

Of these, perhaps the martin and the barn swallow are most closely connected to human. Indeed, humans and barn swallows might be considered almost to be commensal species, species whose activities benefit one another.

Barn swallows originally nested in caves and other natural cavities; today they nest almost exclusively on structures that humans have built. In turn, they eat countless numbers of flying insects.

Plus, they provide entertainment — and practice at ducking flying objects. In many cultures, swallows are considered to be good omens.

The gathering of swallows after a successful nesting season is one of the region’s first signs of the approaching fall. Watch for this. It’s not far off.

Jacobs is publisher and editor of the Herald.

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