The air was thick and clammy, and mosquitoes were biting along Louisiana’s Mermentau River last Thursday morning, the final day of the Audubon Christmas Bird Count. A lone Black-bellied Plover quietly worked the flats amid hundreds of other shorebirds.
Black-bellied (Grey) Plover, Pluvialis squatarola, in California CC-BY Alan Vernon
Remarkable birds, Black-bellied Plovers, winter refugees here from the high Arctic tundra. Their rather nondescript winter nature conceals some fascinating secrets, not the least of which is that they and their closest relatives, the three golden-plover species, are among the planet’s greatest flyers. The golden-plovers can sustain powered flight for at least five days without stopping and regularly cross 3,000-mile expanses of open ocean (that’s more than 4,800 kilometers). Some individuals travel 25,000 miles per year from their breeding grounds on the tundra to wintering grounds near the bottom of the world and back.
The four Pluvialis plovers are sometimes called “tundra plovers” because of their breeding range. I find the name a wonderfully evocative one for these wayfaring travelers with mournful calls and gentle faces. According to the Helm Dictionary of Scientific Bird Names, their genus name, Pluvialis, comes from the Latin word for rain because European Golden-Plovers were believed to call before it rained.
European Golden-Plovers (Pluvialis apricaria) on their breeding ground in Iceland CC-BY Elma
Morphological analyses placed the tundra plovers squarely among all the other plovers — including dotterels, Killdeer, and Snowy and Kentish Plovers — for many years. But their conservative body plans concealed a secret that three molecular studies have exposed within the last decade: The tundra plovers aren’t all that closely related to other plovers.
In fact, it appears that the far-fetched stilts and gorgeous avocets (and you really have to see this one too), the marvelous oystercatchers, and the enigmatic Himalayan Ibisbill all lie between the tundra plovers and the “true” plovers in the avian tree. (See Fain and Houde 2007 and Baker et al. 2007.)
In cladistic terms, this means that including tundra plovers in the family Charadriidae with other plovers makes that family paraphyletic with respect to the other groups mentioned above, which are traditionally placed in their own families. The solution is either to lump them all in one family (an approach which no one seems to like in this case) or to place the tundra plovers in their own family, Pluvialidae.
I am not aware of any major taxonomic authority that has recognized this family-level split yet, however. The American Ornithologists’ Union South American Classification Committee currently acknowledges the situation with a footnote but has not formally acted to resolve it with a proposal and a vote.
Part of the hesitance originates from one of the very papers that reported the molecular results:
While it is tempting to suggest systematic revisions of the Charadriiformes based on our results, caution is warranted because anomalous gene trees that differ from the species tree can be common when sequence data are concatenated (Degnan & Rosenberg 2006). This is especially likely to be a problem when recent branches are long and deeper branches in the species tree are short, as occurs in parts of our tree including the branch to Pluvialis. We therefore advocate prudence until clade markers such as CR1 retroposons can be found to check controversial phylogenetic placements of genera. (Baker et al. 2007)
So though things haven’t moved just yet, it seems likely that additional data will accumulate eventually, compelling action by various taxonomic bodies.
Meanwhile, whether you see tundra plovers on a southern beach, in a muddy inland field, or on the Arctic tundra, take an extra moment to appreciate them for the amazing birds that they are.
European Golden-Plovers (Pluvialis apricaria) CC-BY-SA Ferran Pestaña