Bird Migration Is An Amazing Event
Ro Wauer, April 13, 2003, The Victoria Advocate, © 2003
Spring in South Texas is an exciting time of year! This is when birds of all colors, sizes, and shapes are passing through our area en route to their nesting grounds in Texas and beyond. An incredibly high percentage of all spring migrants pass through South Texas in April and May. Anyone with even the slightest interested cannot help but be impressed with the varieties and numbers. Folks I visit with this time of year are not only awed, but also filled with questions about bird migration. Here are answers to a few of the more common queries.
Where are the migrants going and where are they coming from? Most of our migrants have spent their winters in the Tropical, from central Mexico to South America; a few may have overwintered in extreme South Texas. These Neotropical migrants come north in spring to nest, fanning out all across 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 songbirds passing through South Texas are Trans-Gulf migrants that leave Mexico's Yucatan Peninsula in the early evening and arrive along the Texas Gulf Coast the following day (depending upon weather conditions), a distance of about 550 miles. Songbirds are able to fly nonstop for 80 to 90 hours. You can watch the night migrants passing overhead on a clear night by setting up a spotting scope aimed at the moon; the abundant birds appear as black specks.
Do all birds migrate at night? Most do, but many others, such as swallows and some flycatchers feed in flight, usually migrate during the daylight hours. We see many of these birds flying north over the fields and woodlands of South Texas. Many raptors also fly during the daylight hours, roost overnight, and head out again in the morning as soon as the day warms up enough for them to take advantage of the rising thermals.
How fast do birds fly? Most long-distance migrants travel between 25 and 40 mph. Flight speeds vary, however. For instance, Purple Martins fly at 27 mph, shorebirds fly between 45 and 55 mph, and hummingbirds may fly up to 55 mpg. Raptors sail along with the prevailing winds, but can fly much faster when necessary; Peregrine Falcons, for example, can dive at about 140 mph.
How high do birds fly? It varies with the topography, but 90% of all migrating birds fly below 5,000 feet above ground level. Many fly much lower so we are able to hear chips on a calm day or night. They tend to fly higher at night when flying over land. The Trans-Gulf migrants usually fly very low, often able to take advantage of even the slightest updrafts.
Do birds migrate in mixed flocks? Mixed flocks of songbirds, ducks, and shorebirds are normal, but some species, such as nighthawks and Chimney Swifts usually stick with their own species. In the fall, several raptors species can often be found within one area, but most hawks also stay with their own. However, many species of hawks and other raptors often roost together at choice sites, so that their morning departures incorrectly give the impression that they are migrating in mixed flocks.
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 loses almost 1% 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 hours of daylight in spring. You need not worry about your feeders preventing wintering birds from leaving. Your bird food only helps those birds prepare for their journeys.