Moorhen Mania: The splitting and renaming of the Common Moorhen

One of the items currently before the American Ornithologists’ Union’s North American Checklist Committee (NACC) is a proposal to split Old World and New World forms of the Common Moorhen (Gallinula chloropus) into separate species. The AOU’s South American Checklist Committee (SACC) passed a very similar proposal last year, and the IOC followed suit shortly thereafter. I expect the NACC will pass the proposal this year, and the Clements list will follow, so let’s look at some of the reasons for this split — and the touchy subject of English names for the New World species.

Common Moorhen … or is it? © Corey Finger

Old World and New World moorhens haven’t always been lumped. The AOU treated New World populations as “Florida Gallinule,” Gallinula galeata, in its first checklist (1886) but lumped them into the widespread Old World species in its 18th supplement (1923), between the third and fourth versions of the checklist. Despite the lump, the AOU kept the English name “Florida Gallinule” at first, eventually replacing it with “Common Gallinule,” and finally changing this to “Common Moorhen” to conform with Old World usage in the 1982 34th supplement. This all happened before I was born, so “Common Moorhen” is all I’ve ever known, but I know birders who still struggle with the change.

Alvaro Jaramillo’s proposals to the AOU checklist committees cite recent genetic work and analysis of the birds’ vocalizations to support species status for the two forms.

A 2008 paper by Groenenberg et al. (Ancient DNA Elucidates the Controversy about the Flightless Island Hens (Gallinula sp.) of Tristan da Cunha) set out to examine status of two flightless moorhens from the mid-Atlantic islands of Tristan da Cunha and Gough. In the process, researchers discovered that the two species, one of which is extinct, are more closely related to Old World Common Moorhens than to those sampled from the New World.

On one hand, this can be interpreted as evidence that four species are involved. On the other hand, it’s not at all impossible to think that members of a very widely distributed species could become isolated in remote environments and diverge while the rest of the population maintains reproductive compatibility. However, these results also seem to show genetic distance between Old World and New World forms consistent with isolation, though the number of individuals sampled was not very high.

Vocalizations differ markedly between Old World and New World populations, with New World birds known for their weird cackling and giggling noises, while the calls of Old World birds are briefer and simpler (and less likely to end up in a spooky soundtrack). Xeno-canto has recordings from all over the world for comparison: Common Moorhen. Vocalizations are often important clues in birds’ relationships because they are so important in birds’ social interactions and reproduction.

The most obvious physical difference between the two forms is the shape of the birds’ red forehead frontal shields, nicely illustrated below in photos by Charlie and Mike.

This bird, photographed in the UK by Charlie Moores, shows an elliptical, rounded frontal shield.

This bird, photographed in the Bahamas by Mike Bergin, shows a wedge-shaped frontal shield, wide and flat at the top, tapering toward the base.

So to sum it up, the Old World and New World forms appear to show some genetic distance, at least in one recent study, and they show vocal and modest physical differences. Presumably, they do not have much, if any, natural opportunity to interbreed anyway. The trend these days is to split in such cases, so such an outcome seems logical here too.

But what are the English names for the species after they are split? Both the SACC and the IOC use Common Gallinule for the New World species, reverting to a name many birders still use anyway. The IOC keeps Common Moorhen for the Old World species, which has never really been much in question anyway, as far as I know.

In fact, the SACC had already reverted to “Common Gallinule” even before the split, which you can read about in the ranty and rather amusing Proposal #335. “Those who don’t care about the taxonomy think that the name Moorhen itself is totally absurd,” writes Van Remsen. “The species has nothing to do with moors, per se, and even if it did, we don’t have any gosh-darned moors in this hemisphere.”

Again, the switch happened before I was born, so I don’t get the drama at all, but to Van’s point about moors, there may be another explanation. The Wikipedia Common Moorhen entry cites The Oxford Dictionary of British Bird Names (1993) to say that “moor” here is used in an obsolete sense meaning “marsh.” I don’t have access to a copy of the work to check, but it sounds plausible.

In any case, the word has a fine Old English roots, and certainly doesn’t need to change on the east side of the Atlantic. “Gallinule” is a Neo-Latin creation (originating from the word for “hen”) and for whatever reason has a lot of traction over here.

It seems likely that the AOU NACC will also split the species and call the New World birds “Common Gallinule” — after all, this is simplest and actually has precedent, unlike some of the more novel suggestions. Just for fun, which of these names do YOU prefer, and why? Leave a comment!

• Common Gallinule
• American Moorhen
• Laughing Gallinule
• Florida Gallinule
• Other — please specify!