Split Common Gallinule (Gallinula galeata) from Common Moorhen (G. chloropus)
Effect on South American CL: this proposal would split the New World Common Gallinule (Gallinula galeata) from the Old World Common Moorhen (G. chloropus).
Background: Gallinula chloropus is one of these cosmopolitan species that shows only minor morphological differences over a huge range. There has been little controversy regarding this arrangement, all controversy seems to have been focused on the English name of this bird.
Plumage differences between Old World and New World birds are slight, although bill morphology differs. Old World forms have an elliptical shaped bill shield that is rounded at top, whereas New World forms have a truncated topped shield that is widest at the top.
New information: Recently Constantine et al. (2006) used Gallinula chloropus as an example (pg 139) of how paying attention to sound may “uncover biodiversity.” They illustrate the shield and head shape differences of American and European birds, as well as the longer bill of New World gallinules. But they also describe rather extreme differences in voice between the two populations, publish sonograms and provide examples (on CD) of these differences. What appears to be the primary vocalization in the New World population is a rich nasal “laughter” while the homologous call in the Old World populations is a rather short, simple quavering note lasting less than half a second “kruuuk”. A secondary call type with paired notes is similar in note structure between the two populations, but not in tempo, where differences are apparent. These vocal differences can be heard on xeno-canto, making sure to include examples from outside of the Americas, here is the link that will do this for you:
Groenenberg et al. (2008) recently published molecular data that addresses some species of Gallinula. They were interested in unraveling the relationship of Gallinula on two South Atlantic Islands (Gough and Tristan da Cunha), but also sampled New World and Old World representatives of Gallinula chloropus as well as Fulica. They analyzed molecular data from the D-loop, tRNA-Lysine/ATP8 and cytochrome b. Their result shows Gallinula chloropus to be polyphyletic. They confirm that two separate taxa once inhabited Gough (G. comeri) and Tristan da Cunha (G. nesiotis), and this pair is sister to an Old World group of populations of G. chloropus. Their samples came from Europe, Africa, and Asia. Two samples from the New World (Suriname) are basal to the Old World and Atlantic Island clades. The paper is open access and available here:
In several Gallinula species plumage is conservative, and much of the difference is in the shield shape and color, or in body size. This is parallel to the situation in coots (Fulica). Gallinula chloropus, G. nesiotis, and G. tenebrosa show similar bill coloration of a yellow-tipped red bill with a red shield, although shield shape and size differs. Gallinula angulata is small and has much more extensive yellow on the bill than the other three. Otherwise body plumages are similar, although angulata and chloropus show the white flank stripe, while nesiotis and tenebrosa do not. Leg color varies between species. In essence the bill shape differences between Old World and New World populations of G. chloropus, as well as body size differences (OW birds are smaller), are small, but not that different from currently accepted species within the group.
On the other hand, the vocal differences between OW and NW Common Gallinules are quite extreme, and it does not surprise me that OW populations are sister to the small and flightless Tristan Moorhens, rather than to NW birds. If a wider sample of Gallinula had been looked at in the molecular paper, it is quite possible that other OW Gallinula taxa (tenebrosa and angulata) may also be closer to OW G. chloropus than are the NW birds.
Notes – Galapagos populations sound essentially like mainland South American birds, and respond to playback from Eastern North American birds (Jaramillo pers. obs.). Hawaiian populations are more distinct, and need to be looked at in more detail, particularly with respect to voice. I may have recordings but they are currently not accessible. But overall, they are squarely in the NW population based on shield type. The very large and dark highland (Titicaca Basin) form garmani bears future attention too; again it is clearly a NW form.
Recommendation: I recommend a YES vote, to split Gallinula chloropus. The oldest name for a New World population appears to be galeata (Lichtenstein 1818).
I think we could keep using the English Name Common Gallinule for Gallinula galeata, but note that Constantine et al. (2006) suggest the English Name “Laughing Moorhen” based on its distinctive voice as well as the name cachinnans (Laughing) for the widespread North American subspecies.
Constantine, M. & The Sound Approach (2006). The Sound Approach to Birding: A guide to understanding bird sound. Sound Approach, Dorset.
2008 Ancient DNA Elucidates the Controversy about the Flightless Island Hens (Gallinula sp.) of Tristan da Cunha. PLoS ONE 3(3): e1835. doi:10.1371/journal.pone.0001835
Alvaro Jaramillo, September 2009
Comments from Robbins: “YES. Given that I don’t have access to the Constantine et al. CD, I’m taking at face value that the vocal differences that Alvaro points out on xeno-canto are indeed analogous (there are no on line examples available on MLNS). Having said that, the few examples on xeno-canto demonstrate that Old and New World birds sound nothing alike. Groenenberg et al. (2008) genetic data support this split.”
Comments from Stiles: “YES, at least tentatively. The genetic data for a basal split between New and Old World Gallinula chloropus are convincing, with high bootstrap and Bayesian support; the analysis of vocalizations by Constantine et al. also show strong differentiation between these groups. The morphological differences are not great, but would be in keeping with species-level distinctions in Gallinula and Fulica. Although sampling from the New World was quite limited in the Gough-Tristan da Cunha study, at least in my experience with birds from North, Central and South America sound quite similar and nothing like the Old World birds. I note in passing that this would lay to rest the burning English name controversy over whether to call our birds gallinules or moorhens.”
Comments from Zimmer: “YES. This is one of those groups where plumage characters are evolutionarily conservative, and voice (plus frontal shield color/morphology) is a much better indicator of relationship. And yes, this would finally give us the perfect rationale for getting rid of “Common Moorhen” as the English name for New World birds!”
Comments from Remsen: “YES. All data point towards a minimum of two species within chloropus.”
Comments from Pacheco: “YES. Os dados disponíveis no momento apontam objetivamente para a interdependźncia, ao menos, dos táxons presentes no Velho e no Novo Mundo.”
Comments from Nores: “YES. La propuesta hecha por Alvaro es muy convincente ya que muestra que existen diferencias en vocalizaciones (basado en Constantine et al. y xeno-canto) y genéticas (en Groenenberg et al.). Como Gallinula chloropus era un ejemplo siempre citado de especie cosmopolita, resulta un poco desilusionante esta separación, pero ya hay varios ejemplos similares sobre la relación de especies del nuevo mundo con las del viejo mundo. Por ejemplo Larus maculipennis era considerada una subespecie de L. ridibundus, Larus dominicanus de L. marinus, Himantopus mexicanus de H. himantopus, Phoenicopterus chilensis de P. ruber, Plegadis chihi de P. falcinellus, etc. Otras especies, por el contrario, tales como Sarkidiornis melanotos, Nycticorax nycticorax, Chroicocephalus cirrocephalus, etc. se mantienen y sería bueno ver también si no son diferentes las del Nuevo Mundo de las del Viejo Mundo.”