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Fall Migration of the Ruby-throated Hummingbird

2009-10-28 11:59:00.0

Mary Holland

  Ruby-throated hummingbird

You are a bird weighing between 1/10th and 1/8th of an ounce (that’s 2 ½ paper clips) and you can fly up to 3,500 miles, 500 of which may be nonstop, under your own power.  What’s more, you do so twice a year.  Impossible?  For many years ornithologists assumed so.  There were many theories regarding the phenomenon of ruby-throated hummingbirds crossing the Gulf of Mexico in order to winter in Central America.  One held that these tiny birds hitched a ride on the backs of other, larger birds.  Thanks to the practice of placing individually-numbered bands on the legs of birds and setting up nets in which to catch them, a great deal has been learned about what really goes on during the migration of ruby-throated hummingbirds as well as other species.

It is now known that the ruby-throated hummingbird is the only hummingbird that nests in eastern North America, and winters, for the most part, along the western Gulf coast south through Central America.  Due to the lack of appropriate food, these birds must find a warmer climate during the colder months.  Many fly across the Gulf of Mexico in order to do so, but many also follow the coast line.  Enough birds have been sighted for us to know that, as a whole, ruby-throats fly quite low during migration – just above the trees when over land, and skimming the waves over water.  As those who feed ruby-throated hummingbirds into the fall have probably noticed, males are the first to leave New England.  Adult females are the next to head south, followed shortly by juveniles. Some males leave as early as July, but most hummingbirds depart towards the end of August and beginning of September.  The number of ruby-throated hummingbirds migrating south in the fall may be as much as twice the number that return in the spring, as it includes all the immature birds that hatched out this past summer.

It is widely known that ruby-throated hummingbirds consume nectar and insects.  The overland migration of these birds occurs at the peak of flowering of spotted jewelweed, or touch-me-not, whose nectar ruby-throats are fond of.  Some ornithologists feel that this is not coincidental and that the flowering of jewelweed may even influence the timing of ruby-throated hummingbird migration.

As early as July, ruby-throated hummingbirds start accumulating fat.  According to Cornell’s The Birds of North America Online, a ruby-throated hummingbird’s body weight can double in just seven to ten days.  Research has shown that the average amount of weight gained by hummingbirds prior to migration is sufficient to fuel a 500-mile flight – a necessity if they choose to cross the Gulf of Mexico.  For those who wonder if leaving their hummingbird feeders up late into the fall might delay the birds’ departure, fear not.  The hummingbirds visiting feeders in the fall are probably migrants, not residents, and will help, not hinder, their migration.

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