The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Thursday, August 13, 2009

Fall Bird Migration is Well Underway
by Ro Wauer

Fall in South Texas is an exciting time of year! For birders and other nature lovers who spend time in the outdoors, it is next to impossible not to notice our south bound migrants. They include birds of every color and shape, many of which we might have seen on their way north in spring. It only makes sense to be filled with wonder. And many folks ask about bird migration. Here are answers to a few of the more common questions.

Where are the migrants going? Most of our passing birds are Neotropical migrants, species that spend their winters in the Tropics, from central Mexico to South America, and nest in North America, from Texas to Alaska. Some Arctic shorebirds that winter in southern South America and nest in northern Alaska travel a round-trip distance of well over 13,000 miles.
Most of the springtime songbirds passing through South Texas are Trans-Gulf migrants that leave Mexico’s Yucatan Peninsula in early evening and arrive along the Texas Gulf Coast the following day (depending upon weather conditions), a distance of about 550 miles. A smaller number of those same songbirds also take a Trans-Gulf route in fall. Songbirds are able to fly nonstop for eighty to ninety hours.

Do all birds migrate at night? Most do, but many others, such as hummingbirds that feed on nectar and swallows and flycatchers that are insect-eaters feed in flight, usually migrate during the daylight hours. We see many of these birds flying south over the fields and woodlands during the months of August, September and October.

How fast do birds fly? Most long-distance migrants travel between 25 and 40 mph. Flight speeds vary with their activity. For instance, purple martins fly at 27 mph, shorebirds fly between 45 and 55 mph, hummingbirds may fly up to 55 mph, but peregrine falcons, our fastest known bird, can stoop at over 125 mph.

How high do birds fly? It varies with the topography, but 90 percent of all migrating birds fly between 5,000 feet above ground level. Many fly much lower so we are able to hear clips on a calm day or night. They tend to fly higher at night when flying over land.

Do birds migrate in mixed flocks? Mixed flocks of songbirds, ducks, and shorebirds are normal, but some other species, such as nighthawks and chimney swifts, usually stick with their own species. In fall, several raptor species can often be found within one area, but most hawks also stay with their own kind.

How do birds prepare themselves for migration? Most accumulate great quantities of fat as fuel for their long-distance flights. Many double their weight. The tiny ruby-throated hummingbird, weighing 4.5 grams, uses 2 grams of fat to fly nonstop for twenty-six hours. A typical bird will lose almost one percent of its body weight per hour while migrating.

What is a bird’s signal to migrate? Although the answer is complicated, a simple answer is the increasing or decreasing hours of daylight in spring and/or fall. Arctic birds can raise a family in only a few short weeks, due to the long daylight hours, and often are some of the earliest fall migrants found in South Texas. Most of the earliest fall arrivals are males, while the females remain on their nesting grounds a bit longer to care for the nestlings.


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