Last week I discussed some bird migrants and how far they traveled. Today let’s explain migration a little more in detail.

There are almost 650 species of breeding birds in North America. Eighty percent of those birds migrate. As I noted last week, many migrate as far as South America. Technically, since many of those spend almost six months there, they are basically tropical resident birds that fly north to raise young.

Migration occurs differently among species. Hawks and eagles migrate only during the day. They rely on either rising bubbles of warming air (thermals) or deflecting winds along ridge tops. Most of our smaller birds (warblers, flycatchers, vireos and sparrows) migrate at night. There are two main reasons for this. First, they can avoid most predators better then. Secondly, they need to feed, too. It would be nearly impossible for these birds to find tiny caterpillars (already colored to blend in) in darkness.

If they only migrated during the day, half the day would be spent feeding and the remainder, flying. By flying at night they can “cover a lot of territory” on the longer nights and then use the daytime to drop into the forests to feed and then rest. This allows them much less migration time from the tropics to their nesting area.

How do they know where they are going? How do they get back to the same woodlot? How does a bird less than a year old make it back to the same backyard it was born in? Well, here are some of the best theories.

Those migrating at night have been proved to follow star patterns. But what about cloudy nights? Most bird species apparently use the earth’s magnetic fields as a main guidance tool. The exact specifics are still not known, but experiments with caged birds and changing star patterns on ceilings and altering magnetic fields in labs has shown they are then confused.

The scientists also believe low frequency sounds such as very distant ocean wave sounds can help them stay on course. That still doesn’t explain how their “guidance systems” get them to the same area each year. Will we ever know exactly?

How does a 4-month-old broad-winged hawk know to fly to Peru in South America and it has never made the trip before? (Instinctual? Could be)

The few years I banded birds, I used my live trap to catch juncos. I banded and released them. The next winter I was able to catch some of the same birds, and by comparing the numbers on their leg bands determined I held them in my hands the winter prior. They fed here in winter, flew to New York or Canada to breed, and the next October, were back in Reed’s front yard.

I had the same results with tree swallows banded at home, too. They were back at my nest boxes the next year. I bet some husbands would want this miraculous ability when their significant others have already taunted them a few times, “Honey, I told you to use the car’s navigation. You’re just too stubborn.” Must be a male thing.

Birds’ journeys can be very hazardous. One TV tower in Wisconsin, on one September night, had 2,117 dead birds of 37 different species at its base. City skyscrapers’ glass windows have much the same results.

Then when they drop into the trees to feed, migrating hawks are looking for them, too. Imagine the mortalities of the hummingbirds that can make a nonstop flight across the Gulf of Mexico just above the waves’ surface. Some species of warblers, such as the blackpoll, can fly two or three days along the Atlantic Coast without stopping. Warblers are about 5 inches in size. I guess it explains why their life spans are only a few years.

Maybe we will never know exactly how they do it. There certainly is the drive to perpetuate the species and that is why they migrate. Luckily for the bird-watchers among us they do, and maybe they know we enjoy the diversity of birds here in the Times News area each year.

Remember, I can write about these things, show you a few photos, but get out there and see what nature has to offer.

Test your knowledge: Some warblers have been observed flying as high as ___ feet. A. 5,000, B. 10,000, C. 25,000, D. 50,000.

Last Week’s trivia: The arctic tern is the ultimate migrant, logging about 22,000 miles yearly.

Contact Barry Reed at breed71@gmail.com.