Clapper and King rails may represent four or five species
Clapper and King rails (Rallus longirostris and R. elegans) are the largest rails in the Americas. Their taxonomic status long has been unclear due to their overall similarity and the fact that in eastern North America and Cuba, they hybridize. But some recent work by James Maley and others is shedding more light on these secretive and fascinating birds.
Clapper Rails, as currently defined by the AOU, occur along the coasts of North and South America and Caribbean islands, and inland in southern California and Arizona. The photo above, one of mine, shows a Clapper Rail in Louisiana. King Rails occur widely in eastern North America, in eastern and central Mexico, and in Cuba.
In eastern North America, birders think of King Rails as richly colored birds of freshwater marshes, while Clapper Rails are considered drabber birds of saltmarshes. In California and Arizona, however, Clapper Rails are brightly colored and occur in both salt and freshwater environments. South of the ABA area, the picture is further complicated, but more on that in a bit.
Clapper Rail of the grayish U.S. Atlantic Coast subspecies crepitans in New Jersey by Corey Finger
In his doctoral dissertation — Ecological Speciation of King Rails (Rallus elegans) and Clapper Rails (Rallus longirostris) — for Louisiana State University, James Maley uses new genetic analyses and other data to identify three major groups within the Clapper-King complex:
- An eastern clade comprising Clapper Rails of eastern North America and the Caribbean plus all King Rails except those of the central Mexican highlands;
- A South American Clapper Rail clade;
- A clade comprising Clapper Rails of California, Arizona, and northwest Mexico plus King Rails of the highlands of central Mexico.
Maley then goes on to examine the hybrid zone between Clapper and King rails in Louisiana, finding that the hybrid zone is very narrow (about 4 kilometers, or 2.5 miles) and appears to depend on the presence of brackish marsh; where saltmarsh and freshwater marsh were immediately adjacent due to human manipulations, he found that birds did not interbreed.
High quantities of salt can be deadly to birds (and many other living things), so rails living in saltwater environments have glands in their heads that excrete extra salt to maintain an internal balance conducive to life. In freshwater rails, this gland is smaller, and the birds do not fare well in saltier environments.
Maley’s genetic work shows that the saltwater and freshwater populations are maintaining their distinctiveness in Louisiana. The birds’ mitochondrial DNA shows that, despite rails’ propensity for long-distance travel, the freshwater and saltwater populations are not two ends of a spectrum but rather maintain their distinctiveness despite the occurrence of hybridization in brackish environments. The full study is fascinating and well worth a read.
King Rail and chick in Illinois cc-by Andy Reago
So, Maley suggests recognizing four species, instead of the two currently recognized. These would be as follows (no English names proposed):
- Rallus longirostris of South America, comprising the subspecies longirostris, phelpsi, margaritae, pelodramus, cypereti, and crassirostris. All of the subspecies in this complex are currently treated as part of the Clapper Rail complex. They are pale, thick-billed birds of mangrove environments.
- Rallus obsoletus, which would include the subspecies obsoletus, levipes, yumanensis, and beldingi of California, Arizona, and northwest Mexico, plus tenuirostris of freshwater wetlands in the central Mexican highlands (this population is currently treated as part of the King Rail complex). These birds are all relatively brightly colored. The Pacific Coast populations are endangered.
- Rallus elegans, which would presumably keep the name King Rail and would include the subspecies elegans of eastern North America and ramsdeni of Cuba. These are brightly colored birds that breed in freshwater environments.
- Rallus crepitans, variably colored saltwater birds of eastern North America and the Caribbean, including the subspecies crepitans, waynei, scottii, insularum, saturatus, caribaeus, pallidus, grossi, belizensis, leucophaeus, and coryi.
So when might we see the AOU or other bodies deliberate this information? Maley has a forthcoming paper in The Condor (Mitochondrial and Next-Generation Sequence Data Used To Infer Phylogenetic Relationships and Species Limits in the Clapper/King Rail Complex) that should provide the published evidence needed for taxonomic bodies to act, or at least open the discussion.
I should also note that the abstract for the Condor paper proposes five, not four, species. Perhaps tenuirostris of Central Mexico is proposed as a full species, instead of being lumped with the endangered Pacific and Baja populations?
What do you think? Do the arguments in Maley’s thesis make sense to you? What English names would you propose if the complex is split into four or five new species? And what are the conservation implications of elevating the endangered Pacific populations to full species status?