[edited 12 Feb 2008]
From Texas comes the remarkable news of the discovery of an apparent White-crested Elaenia (Elaenia albiceps) found by Dan and Honey Jones on 9 Feb 2008. Photos, sound recordings, and ID discussion can be found at Martin Reid's website and some great photos at Erik Breden's website. The bird was found at the Sheepshead Woodlot sanctuary (preserved by the Valley Land Fund) on South Padre Island. [Update: after being seen by many on 10 Feb, the bird could not be found on 11 Feb; hopefully it will reappear]
Given that South Padre Island is a barrier island on the Gulf of Mexico, just north of the Mexican border, it has a distinct geographic advantage when it comes to attracting rare birds. But this particular species could have turned up almost anywhere. The fact that it landed just across the Mexican border would seem to be just a fluke (although one can't discount observer effects: birders on the Mexican border tend to be a little more open to these possibilities when an "odd" bird is found). White-crested Elaenia is a South American species, nesting in Chile and Argentina during the southern summer and migrating north to winter (during the southern winter) in the Amazon lowlands. [update: to clarify, this is referring only to the migratory southern "Chilean" subspecies, which may be a different species from the more or less sedentary populations in the Andes farther north. I'm assuming that the Texas bird is from the migratory southern population.] Fork-tailed Flycatcher is another austral migrant, and a more familiar vagrant in the US and Canada.
So let's speculate about some dates: If this is a young bird it most likely fledged sometime around January 2007, about one year ago. Then in April it migrated north to the lowlands of Brazil, where it stayed for the few months of the southern winter. In October 2007 it would have been ready to migrate back to its breeding range in southern South America, and presumably at that point it made a mistake and migrated north instead of south, bringing it to North America. Right now it should be on its breeding grounds, in mid to late summer. The urge to migrate should have waned in December, but maybe this bird found itself in some inhospitably cold place and was forced to move south for food, bringing it to South Padre Island. Or maybe it's been in that area since last fall. Or maybe this bird's clock, along with its navigation system, is screwed up and it's just off on a wild adventure. We'll never know, but given that the species has a range and migratory pattern like Fork-tailed Flycatcher [wrong - see note below], it is plausible that its patterns of vagrancy would be similar, and that suggests the scenario that this individual arrived in North America about three months ago.
The breeding range of this species is centered about 5000 miles (in a straight line) from South Padre Island, which is a remarkable distance. Small changes in direction of flight, or distance, would bring the bird to very different locations. It could just as easily have turned up at any of the Gulf Coast barrier islands, or a desert oasis like Big Bend, and traveling just 20% farther would bring most of the eastern US within its range! Something to watch for....
Note: Thanks to Chris Vogel for pointing out some flaws in my speculation, which reveals my ignorance of South American birds (and a lack of research). The range and migratory patterns of White-crested Elaenia and Fork-tailed Flycatcher are not very similar after all. Here are maps from Natureserve's InfoNatura database showing the ranges - Fork-tailed Flycatcher (left) and White-crested Elaenia (right)
both images © 2007 NatureServe, 1101 Wilson Boulevard, 15th Floor, Arlington Virginia 22209, U.S.A. All Rights Reserved.
White-crested Elaenia nests in the highlands of western South America, Fork-tailed Flycatcher in the lowlands of eastern South America. There is little overlap in breeding range and the migratory patterns must be quite different. Chris stresses the fact that altitudinal movements are a significant part of the Elaenia's migration, from colder mountains to warmer lowlands, while Fork-tailed Flycatcher is a lowland bird all year. Anyway, the main point I was trying to make is that both species are long-distance austral migrants (at least partly) and the Elaenia (like Fork-tailed Flycatcher) could have turned up almost anywhere in North America as easily as at South Padre Island.