The Rufous Hummingbird is North America's “extremist” hummingbird, widely known in the west for its aggressive nature. Venturing far from the equatorial tropics in which its ancestors evolved, it reaches the northernmost latitude of any hummingbird (61° N). After making the longest (measured in body lengths) known avian migration, individuals from Alaskan populations face a short breeding season but the longest day-length seen by any hummingbird.
Increasingly this hummingbird has been recorded as a fall and winter vagrant in the southeastern (and even the northeastern) US. Whether this is a new trend, or one detected simply because of the growing interest and sophistication of birders, and more numerous hummingbird feeders, remains unclear. But no other western hummingbird is known to wander to this extent -- another reflection of this “extremist” bird.
Energy demands for hovering flight and temperature regulation of tiny bodies draw special attention to hummingbirds, of which the Rufous has become one of the best known physiologically. And it is uniquely suitable for studies of hummingbird migration. In the 1,500+ km belt separating its southern limits of breeding and northern limits of wintering, all observed Rufous are transients, providing an opportunity to study migration free of confusion with local breeders. In July and August, large numbers of southbound Rufous, refueling on the seasonal abundance of subalpine and alpine flowers, have become a model system for investigating foraging behavior and pollen transfer.
Although well studied physiologically and in migration, this hummingbird remains poorly known in most aspects of its life history, particularly breeding ecology and population dynamics. Bent's ( Bent 1940a ) life history account provides a glimpse of individuals at the nest, with some interesting anecdotal accounts, but no quantitative breeding study has followed that in over 60 years. Recently, Rufous Hummingbirds on their breeding grounds have proven to be useful for investigating cognitive abilities, both in the laboratory and in the field (e.g. Bateson et al. 2003 , Brown and Gass 1993 , Healy and Hurly 2003 , Henderson et al. 2006 ). Furthermore, the ease with which this species can be kept in the laboratory has lead to significant discoveries concerning hummingbird flight mechanics and physiological capabilities (e.g. Chai and Millard 1997 ; Lotz and Rio 2006 ; Wells 1993a ).