Published September 02, 2012, 05:00 AM

ALWAYS IN SEASON: Bird behavior reflects change of seasons

Much of the summer, I’ve wondered how many swallows my buildings hosted. Swallows are hard to count, though. They rarely stay still. Instead, they’re aloft or in flight, resting (briefly) or chasing airborne insects. A peculiar combination of conditions produced an opportunity to count the swallows last week.

By: Mike Jacobs, Grand Forks Herald

Late one afternoon last week, the barn swallows at my place west of Gilby, N.D., presented themselves for a census.

This was a welcome development.

Much of the summer, I’ve wondered how many swallows my buildings hosted.

Last week, I made a guess, somewhere around 50, I figured.

This estimate was backed by some observation. This year, there were four swallow nests on buildings at my place. Each nest produced two broods of four or five birds each. With the adults, that would be upwards of 40 birds.

Swallows are hard to count, though. They rarely stay still. Instead, they’re aloft or in flight, resting (briefly) or chasing airborne insects.

A peculiar combination of conditions produced an opportunity to count the swallows. It was a hot day — as most days were last week. There was little wind — something unusual in the Red River Valley.

The swallows alit at the top of a Siberian elm tree. I counted them several times. Every result was 44 to 47 birds. Allowing for the occasional stray, this suggests a total of 45 birds or so.

Unfortunately, I can’t be sure how many are adults and how many are young of the year. It seems reasonable to assume that all of the nesting adults survived the summer.

That would be eight. That would leave about 37 (plus or minus one or two) young birds.

This arithmetic suggests an average of 9.5 young per adult pair.

Each of the nest produced two broods, or an average of 4.25 birds per brood, arithmetically speaking.

This seems close to correct observationally.

I counted five eggs in a nest over the door that leads to our deck, and I counted five young birds in a nest above the door of the garage.

There was a single bird in the nest on Saturday morning. It’s September, of course, and I briefly worried that the bird had been left behind. Not so, however. As the day warmed, more swallows appeared. Migration, it seems, hasn’t yet begun for swallows.

Swallows have a tendency to simply disappear.

One day in early autumn, flocks of swallows line overhead electrical and telephone lines — and one day they’re gone.

This phenomenon baffled early naturalists. For centuries, even the most sophisticated ob-servers thought that swallows must disappear into the Earth.

Aristotle considered this. Gilbert White accepted it. Aristotle was the greatest of Greek naturalists, active several centuries before Rome became an international power. White was a pioneering English naturalist, author of “The Natural History of Selbourne,” one of the classic works of natural history in English, He wrote about the time of that the United States emerged as a nation.

The idea that swallows hibernate seems absurd today. We know that swallows are long-distance migrants.

The idea that swallows might burrow into the earth isn’t so far-fetched, however. In fact, they do just that.

Several species of swallows nest underground. Aristotle and White would have seen swal-lows entering and leaving tunnels in mud banks and coastal cliffs. This behavior is familiar to North American bird watchers. One of our most abundant swallow species, the bank swal-low, behaves in just this way.

So, it’s not so great a leap to imagine that the birds might spend the cold months under-ground.

It’s a bigger leap to accept the idea that hummingbirds migrate on the backs of geese. This notion is widespread in folklore. It must have arisen because hummingbirds seem impossibly small to make any long-distance flight.

Hummingbirds are very strong fliers, however. They are fully capable of making their way across the Gulf of Mexico, a twice-yearly route for them.

This is the season for hummingbirds, as it is for swallows. Numbers of hummingbirds and numbers of swallows increase as fall advances and the migration imperative increases.

For me, hummingbirds and Labor Day have a strong association.

The only hummingbird species to expect locally is the ruby-throated hummingbird. A cou-ple of other species have been reported in our general area — the Upper Midwest — but they are accidental at best.

Ruby-throated hummingbirds are nesters here, but they are more common farther east and farther north. It’s these northern birds that we see here at this season.

Even though hummingbirds and swallows are small birds, their appearance and behavior is sign of the season every bit as much as the huge flocks of waterfowl that we anticipate as autumn advances.


Jacobs is publisher of the Herald.

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