Hummingbird migration: Difference between revisions

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Hummingbirds are a family of small, primarily nectar-feeding birds that are indigenous to the Americas and the islands surrounding them. As with many other major bird groups, many species of hummingbirds leave their summer grounds upon onset of winter and migrate to more tropical areas near the equator, as do many other bird species in general. Migration lengths and routes vary by species, with some, including the rufous hummingbird, migrating as much as 4000 miles from Alaska in the north to Mexico in the south, while others, such as the giant hummingbird of the Andes, only migrate a few hundred kilometers down the slope of the Andean ridge. The ruby-throated hummingbird (the only primary species in Eastern North America) can summer in southern Ontario and then migrate as far south as Mexico and Guatemala, with males returning earlier than females by about 2–3 weeks to ensure they have already established their territories by the latter’s arrival.

Relatively few hummingbirds migrate as a percentage of the total number of species; of the roughly 330 known hummingbird species, only 12–15 are currently known to undertake annual migrations. The primary reason for this is because the vast majority of hummingbirds live in the Amazonia-Central America tropical rainforest belt, where seasonal temperature changes are relatively low.^[1]

Hummingbirds, being the smallest living birds, are relatively limited at conserving heat energy and thus, are generally unable to maintain a presence in higher latitudes during winter months, unless the specific location has a large food supply throughout the year. The green-backed firecrown, of the Southern Cone of South America, migrates no farther north than 30 S and no farther south than 54 S at any time of the year, never traveling more than a few hundred kilometers either way (though the species is notably absent from the Argentinian lowlands during the summer months).^[2]

It has been suggested that some, such as the rufous hummingbird of the west, base their migration patterns on the blooming of certain flowers, not the presence of warm or cold weather. A primary flower species preferred by the rufous, the Indian paintbrush, only blooms during the late spring and early summer months (May–June), and thus the overall time spent in their northern summer grounds is much less than one might expect.^[3]

Most North American hummingbirds migrate southward in fall to wintering grounds in the Southern US, as well as in Mexico, Central America, and the Caribbean. These include the rufous hummingbird of the west, which is famous for its long migrations from northern Canada and Alaska to Mexico, the ruby-throated hummingbird of the east which migrates from Atlantic Canada and New England to the Southeast states (especially Florida) and the buff-bellied hummingbird, a winter resident of the Gulf Coast states.^[4] Ruby-throated hummingbirds are common along the Atlantic flyway, and migrate in summer from as far north as Atlantic Canada, returning to Mexico, South America, southern Texas, and Florida to winter.^[5]

The rufous hummingbird is the northernmost-breeding of any hummingbird, By migrating in spring as far north as the Yukon or southern Alaska, the rufous hummingbird migrates more extensively and nests farther north than any other hummingbird species, and must tolerate occasional temperatures below freezing in its breeding territory. This cold-hardiness enables it to survive temperatures below freezing, provided that adequate shelter and food are available.^[6] In terms of the length of the migration compared to the size of the bird, rufous hummingbirds have the longest migrations of any bird species. The northward migration of rufous hummingbirds along the Pacific flyway is likely time-coordinated with the blooming of key flower species (including the Indian paintbrush as described above). ^[7] Arrival at breeding grounds before nectar availability from mature flowers may jeopardize breeding opportunities, and leaving these grounds too late may leave the birds vulnerable to freezes.

• Bird migration
• Hummingbird