HARLINGEN, Texas (ValleyCentral) — It may not feel like it, but the seasons are shifting in South Texas. As daylight decreases, primordial urges prevail, and the world’s smallest migratory bird is one of the first to divulge that fall is in the air.

Ruby-throated hummingbirds are some of the earliest to migrate southward, and their vanguard is already winging it thru the Rio Grande Valley.

Pausing briefly to refuel on blooming plants, insects, and backyard feeders, these tiny dynamos, weighing approximately one-tenth of an ounce or about the weight of a penny, will often double their body weight before embarking on migration.

From nesting grounds as far north as frigid Canada, these intrepid travelers will fly some 2,000 miles to wintering habitat in tropical Mexico and Central America.

Those extra fat reserves they pack on while refueling in the Valley will be sorely needed, as many ruby-throats fly nonstop across the 500-mile swath of the Gulf of Mexico, an arduous journey of some 18 to 22 hours.

During spring migration, male ruby-throats will begin their northward flight in advance of females as they rush to establish prime breeding territories, while the fall passage is less urgent, with females tending to lead the way.

Hummingbirds migrate as solitary flyers, rather than traveling in large flocks, and while each individual’s instincts trigger embarkation on their remarkable migration, it can get crowded at favorite stopovers throughout their journey.

Banding records reveal that ruby-throats have great fidelity to their chosen migration route, and individual birds have been documented to arrive at the same location year after year, sometimes on the same day.

These tiny travelers are thought to utilize a variety of senses to guide them on their instinctual spring and fall migrations including visual landmarks, celestial navigation, and a built-in magnetic compass.

Since the record for longevity for a ruby-throated hummingbird is more than nine years, you just might see an old feathered friend at the backyard feeder this time of year.