08/29/2013 12:32 pm ET Updated Oct 29, 2013

A Rail in Passing

The surprising occurrence of a Rufous-necked Wood-rail in the Bosque del Apache National Wildlife Refuge of New Mexico earlier this summer caused quite a stir among birdwatchers across the United States. It had not been seen before in our country, and is otherwise a fairly rare and local denizen of mangroves from tropical Mexico south to northern South America. It isn't a migratory species, and like most rails, a fairly weak flier. It defies logic, yet it was unequivocally there. One in a million.

My New Mexico friends sent me notices of the sighting and hoped I could come see it. Indeed, I am a regular visitor to "the Bosque" having gone to graduate school at the University of New Mexico way back when and having visited often with my wife, Shawne, and her extended family in New Mexico when we are there for the holidays.

Most such rarities add to birdwatcher life lists, but are usually "noise" in the larger picture of birds as they don't signal durable range shifts. Indeed, this wood-rail hasn't been seen again since late July. Some rare sightings, like those of eastern warblers winding up in the far west during fall migration can be understood as the result of "mirror-image misorientation" as noted and verified by my colleague David DeSante many years ago on the Farallon Islands off San Francisco. The misorientation seems to be the result ofy the birds' moving on a westerly bearing off a north-south axis as a mirror image movement of their normal easterly bearing,

Many, if not most rarities result from extreme weather moving them far afield. There was a Snowy Owl in Hawaii two years ago, at a time when many boreal and arctic species were seen far south of their normal distribution in the winter. Seabirds and other more marine species are often pushed inland by hurricanes or winter storms. I saw a Magnificent Frigatebird off the coast of Rhode Island with a class of students years ago, apparently pushed north of the Gulf of Mexico by a tropical storm or hurricane. And so on.

The Rufous-necked Wood-rail wasn't likely driven by weather, nor did migratory misdirection account for it ending up in the Bosque. Yet its movement is a reminder of the historic capacity of rails to move great distances and colonize new habitats. They did so across South Pacific islands repeatedly. Rails colonized most all islands of the South Pacific, and often did so with very long flights that make one reconsider their apparently weak flight capacity. Interestingly, many species that made those long aerial journeys between islands subsequently evolved flightlessness on their newly found islands. It is one of the great stories from the world of birds. According to the avian paleonolologist David Steadman, whose remarkable studies of fossil birds across the Pacific brought this story to light, perhaps as many as 1600 rail species resulted from this dramatic pattern of island colonization, flightlessness for many, and subsequent colonization to new islands of others. Sadly, most of these rails were driven to extinction with the subsequent movements of people and their associated rats and disease across the Pacific.

I am a mediocre birdwatcher, but am an impassioned student of bird distribution, of avian biogeography specifically. I appreciate most seeing the birds or bird groups unique to the regions I visit in my far-flung travels and in understanding something of the evolutionary and geographic issues that frame their uniqueness. Seeing the Shoebill in my recent trip to Africa, as well as the new Turaco species was fabulous. Rheas, Screamers, and Tinamous in Patagonia were very exciting to see. I spent years in Madagascar and encouraged my Malagasy students to study their unique birds like the Asities, Ground-rollers, Mesites, and Vanga Shrikes.

Most bird groups moved and evolved with the continental movements that have shaped our planet. The breakup of Gondwanaland (the great southern land mass) started to create such distinctions. South America has the most species and the most unique families. Australia (place of much early bird evolution, then isolation) and Madagascar (an unclear mix of bird groups rifting out from Africa and those that colonized) are the most distinctive. Africa and Asia share a long history and so are less distinct as tropical continents. North America is, well, perhaps the least interesting among the continents in this regard. Our continent has been isolated from the other continents for much of its history, and Pleistocene glaciation caused havoc and likely species loss. Turkeys (two species, one in Mexico) are the most distinctive group of birds we have.

The Rufous-necked Wood-rail has come and gone from New Mexico and North America. It added a species to the list of many birdwatchers and is a reminder of a larger story played out in the Pacific.