It’s in your nature: Migrations: Why and how
About 25 years ago, our family was camping at Assateague Island State Park. An early riser, I usually woke before anyone else and would sit in a folding chair to soak in the sounds of the waves rolling in and keeping an “eye out” for anything nature offers. (The campsites are about 100 yards from the surf.)
That particular year our camping week began about Aug. 21. As the sun was just breaking the horizon, swallow after swallow after swallow was zipping by me heading south. Sometimes three or four, usually dozens at a time were in view at the same time.
I sat there enjoying the free nature show for at least 90 minutes and I’m sure I observed a few thousand swallows. Probably 95% were barn swallows, but a few bank, cliff and rough-winged swallows were among the migrants.
Migration intrigued me as a youngster and still does today. Those barn swallows were heading to winter homes after leaving farming plots from Maine, Vermont, New York state and southern Canada. Heck, maybe one or two were feeding over Troxell’s, Gaston’s, or Schoenberger’s farm fields a day or two ago. I know these flying insect eaters need to migrate because their food will disappear in fall. Losing their food provides the “why” they migrate.
Now, the “how.” How does a barn swallow hatched in a nest in the Times News area in June know when it is time to go? Just as intriguing, when or how did it learn where to go? I’m willing to bet that the swallows I saw that day at Assateague all began their migration about the same time, probably between Aug. 15 and 21. Their “nature clocks” were all set about the same. Swallows migrate during the day. Their swift elusive flights allow them to evade most avian predators, and besides, they feed “on the wing.”
The next “how.” How do warblers, vireos, flycatchers, tanagers or orioles, which migrate at night, navigate? Since they feed in the forest canopy or shrubs during the day, they can’t migrate then. They begin their migration at night, without GPS, and still find their winter feeding grounds. Most of them, young from this year, never made this flight before.
Researchers believe that star patterns, magnetic fields and maybe even extremely distant sounds from the ocean help guide them. In spring, they reverse their route and, amazingly, usually return to the same woodlot or forest where they lived the year before. (Note: these night flying birds avoid predators migrating at night, but skyscraper lights, transmission towers and guy wires take a big toll)
Another “why.” Why is it important that they reach the same wintering areas and why is it important that they find the same neighborhood where they were born? If all the barn swallows decided to stop in Bucks County at a farm and try to nest there, they wouldn’t find enough barns in which to nest, nor enough food to eat. The dispersal back to areas from where they were born helps “spread out” the population. Likewise if in winter they all tried to remain in Panama (for example) there wouldn’t be enough food for all of them there. Nature always amazes me, how about you?
Test Your Outdoor Knowledge: Hawk Mountain’s highest DAILY count of broad-winged hawks was ____ thousand. A. 3, B. 7, C. 11, D. 20.
Last Week’s Trivia Answer: The hard fruiting body of a shelf fungi is called a conk.
Contact Barry Reed at firstname.lastname@example.org.