The Ruby-throated Hummingbird, eastern North America's only species of breeding hummingbird, is a familiar summer inhabitant of woodlands, parks, and gardens from central Canada to the Gulf Coast. In geographic area, this species occupies the largest breeding range of any North American hummingbird. In the United States, the western boundary of its breeding range ends along a remarkably straight north-south line, just east of the 100th meridian. This distribution, as well as that in west-central Canada to British Columbia, conforms closely to the range of eastern deciduous and mixed boreal forests ( Bertin 1982b ).
Adult females of this species have an average mass of only 3.5 grams, adult males just 3 grams. Despite their tiny size, many of these birds fly nonstop across the Gulf of Mexico during fall and spring migration, a round-trip of more than 1,600 km. To accomplish this, individuals often double their body mass by fattening on nectar and insects prior to departure. The proportion of this species following a trans-Gulf versus circum-Gulf route is largely unknown, as is regional connectivity in migration routes and wintering areas.
Although the Ruby-throated Hummingbird is widespread and much-loved species, many fundamental aspects of its migration and breeding ecology remain poorly understood. At the time of this writing, for example, there is not single study of nesting success in this species.