Reflections in Nature: Where the wild goose goes
Where the wild goose goes
So far this has been an autumn with temperatures staying higher than normal. Although the leaves on the trees were late in changing colors, as I’m writing this column, many trees still retain their leaves.
We have birds that have not migrated south, and I have seen only a few northern flocks of geese winging south.
Birds do not migrate without proper physiological stimulus. After the breeding and the molting season in late summer, the metabolism of migrating birds undergoes a profound change.
Hormones are released at different times of the day by the pituitary and adrenal glands. When this occurs, a bird begins to accumulate large amounts of fat just under the skin.
For example, the migratory blackpoll warbler, which normally weighs 11-12 grams, could weigh 20-23 grams at the time of the fall migration. This is enough fat reserve for the blackpoll warbler to fly 85 hours nonstop over the Atlantic Ocean to the mainland of South America.
Cold weather also stimulates birds to begin migration. Since the journey is exhausting, some birds have stopping points along their routes where they eat lots of food to replenish their fat reserve in preparation for the next flight step. These changes in physiology are unique to migrating birds.
Of all North America’s land birds, night hawks and barn swallows have the longest migration route, going 7,000 miles to Argentina.
The American golden plovers, which have one of the most interesting migrations, nest in the tundra. After their nesting season, the birds assemble in Labrador and travel over 2,400 miles across the ocean to Brazil, Uruguay and Argentina.
In the spring, they travel a different route over South America to Central America, across the Gulf of Mexico and up the Mississippi Valley to their tundra breeding grounds, a trip of almost 8,000 miles north to south and 2,000 miles on an east-west axis.
Some birds, mostly songbirds, migrate by day, while others (woodcocks) migrate by night and still others (geese) migrate both day and night.
Weather and wind directions affect migrations. Birds generally migrate with a tailwind; however, if the wind changes to a head wind, the birds will land and wait for it to change. Strong winds will stop a migration no matter what direction it is coming from. The wind even may cause a migration to reverse or retreat, especially in the spring when the birds meet a sudden cold front.
Birds migrate faster in the spring than they do in the fall. Sometimes the northern migration is made in half the time that it takes for the southern migration. The speed of the migration varies with species.
Our robin is a rather slow migrator, averaging about 38 miles a day. Smaller birds can have flights of 90 to 200 miles and then stop to rest; however, most will average 65 miles a day. Waterfowl and shorebirds fly much farther, usually 500 to 1,000 miles in a day, but will also stop and rest for several days.
One shorebird, a lesser yellowleg, which had been banded on Cape Cod, Massachusetts, was found dead in the West Indies — 1,900 miles away — six days after being banded.
Some of our swiftest flyers among American birds are the small sandpipers of the coastal areas. Therefore, it was no surprise when Swedish scientists found that great snipes — close cousins of sandpipers — migrate nonstop over a distance of about 4,200 miles at a phenomenal speed of 60 mph.
Apart from its long, elegant beak, the great snipe looks like any other wading bird, but it could well be the fastest bird (over long distances) on earth.
Bower retired after 34 years as a wildlife conservation officer for the state Game Commission. Questions and comments may be sent to him at 1224 Redington Ave., Troy PA 16947.