Although field observations reveal the obvious about Ruby-throated Hummingbird, Archilochus colubris--they occur in North America in summer and in Mexico or Central America in winter--science is lacking in specific details about what routes they follow to get from one place to the other.

There's good evidence that hummers do not fly very high during migration. Over land it is unlikely they get much above treetop height--the better for them to see potential food sources along the migratory route. Hot air balloonists have reported RTHUs at altitudes of up to 500 feet or so. It is certain that hummingbirds would never be able to survive cold temperatures at high altitudes used by waterfowl and larger songbirds, which helps refute the ludicrous myth that hummers hitchhike on the backs of Canada Geese. Over water, hummingbirds have been reported to migrate just above the wave tops; one observer even claimed some hummers get within the curl of a wave, thus allowing the wave itself to serve as a windbreak.

Little is known about fall migration routes in RTHUs. It was once thought that nearly all RTHU from the U.S. flew to Florida in autumn before crossing the Gulf of Mexico to Mexico's Yucatan Peninsula. Some migrant RTHUs apparently do fly from Florida to the Yucatan; however, many RTHUs gather in Louisiana or Texas in mid-September before flying across the Gulf, and some may take an overland route through Mexico. Even less is known about spring migrational paths, but are reported to move north roughly following the 1.7° C isotherm (average nightly temperature); since this is just above freezing (i.e., 0° C), RTHUs are pushing the limit as far as being able to find insects and flowering plants that don't thrive at below-freezing temperatures.

The earliest arrival during spring migration of a RTHU at Hilton Pond Center for Piedmont Natural History were adult males that arrived on 27 Mar in 1991, 2011 & 2014; a previously banded adult male returned on 26 Mar 2015. The earliest adult female was on 8 Apr 2002. The latest encounter with an unbanded bird was a young female on 18 Oct 1986, while the latest adult males were banded on 14 Sep in 2002 & 2014. (Just as adult makes are first to arrive in Spring, so are they first depart in Autumn.)

The map below indicate the average approximate arrival date for the first RTHUs of the spring season in the U.S. and Canada. Factors such as microclimate, altitude, etc., may have an effect on actual arrival dates for specific locations; all these are appropriate for further study.

Click HERE for larger map

All text, maps & photos © Operation RubyThroat & Hilton Pond Center
Satellite image courtesy

Approximate spring arrival dates and breeding range derived from Operation RubyThroat reports, personal experience, and various Web and print sources. Special thanks to Hummingbirds of North America by Sheri L. Williamson.

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