Pacific Horneros always have pale legs but some do not consider Pacific Horneros to be Pale-legged Horneros. That is, Pale-legged Horneros Furnarius leucopus have, according to some, a subspecies called F. l. cinnamomeus, but others consider F. l. cinnamomeus to be the Pacific Hornero Furnarius cinnamomeus, a species in its own right. Which is my convoluted way of saying, once again, that figuring out how many species one has seen is not always as straightforward as one might think. Fortunately for me (I guess) the only hornero I have ever seen is either Furnarius cinnamomeus or Funrarius leucopus cinnamomeus, depending on who you talk to, so I only have one tick to worry about on my checklist. Because I use the International Ornithologists Union (IOC) checklist for all my world listing needs that means that the bird that I check off my checklist is the Pacific Hornero. But why is this bird’s species identity up in the air? Way back in 1992 Parker and Carr decided the Pacific Hornero was a species in its own right and Robert Ridgely and Paul Greenfield agreed in their excellent field guide, The Birds of Ecuador.*
The IOC has decided that this is enough information to split but the South American Classification Committee of the American Ornithologists’ Union (SACC of the AOU) rejected a proposal to split the species with the following justification:
The subspecies cinnamomeus of W. Ecuador and NW. Peru may deserve recognition as a separate species from F. leucopus (Ridgely & Tudor 1994) and was treated as such by Parker & Carr (1992) and Ridgely & Greenfield (2001). The subspecies longirostris was also treated as a separate species by Ridgely & Greenfield (2001) and Hilty (2003). Although vocal and behavioral differences have been reported, no real analysis has been published to support these splits. SACC proposal to elevate cinnamomeus to species rank did not pass because of insufficient published data.
Interestingly, the decision not to split cinnamomeus was not unanimous, and was, in fact, a close 5-3 vote. Clicking on the link from the block quote above will allow you to see not only the proposal, submitted by Van Remson, but also the justifications for the different committee members’ votes on the proposal. The background information offered by Van Remson in his proposal (which he actually voted against) is fascinating, at least to me, and is quoted in full below.
For most of their history, the taxon cinnamomeus has been treated as s subspecies of Furnarius leucopus (Pale-legged Hornero). They are allopatric (nearly parapatric) taxa with no known contact zone; cinnamomeus is endemic to the Marañon valley and western Peru and Ecuador, whereas leucopus is found east of the Andes. No published data exist on characters directly relevant to assessing potential interbreeding such as vocalizations; voices are described as being different, but analysis has not been published. The difference in iris color (pale in cinnamomeus, dark in leucopus) has potential as an isolating mechanism. They are 100% diagnosable phenotypic units based on plumage characters. The primary differences in plumage are (apparent) degree of pigment saturation, with cinnamomeus paler ventrally and duller, darker dorsally. There are no pattern differences. Cinnamomeus is significantly larger in body size. In my opinion, qualitatively, the plumage differences are less than those among the subspecies of F. rufus, and the difference in body size is substantially less. Cinnamomeus also differs less in plumage from leucopus than do sympatric F. leucopus and F. torridus.
Cory & Hellmayr (1925), Peters (1951), Meyer de Schauensee (1966, 1970), Vaurie (1980), and Sibley & Monroe (1990) treated them as conspecific. Parker & Carr (1992) treated them as separate species but I cannot find a discussion of the problem therein. Ridgely & Tudor (1994) continued to consider them conspecific, but noted that cinnamomeus and perhaps isolated longirostris of N Colombia and NW Venezuela may represent separate species. Ridgely & Greenfield (2001) recognized cinnamomeus as separate species. Hilty (2003) treated longirostris and cinnamomeus as separate species. Remsen (2003) maintained them as conspecific but noted that cinnamomeus almost certainly deserved species rank.
So the iris of cinnamomeus, as you can see from my photos,** is pale as opposed to the dark iris of the rest of the Pale-legged Hornero subspecies, cinnamomeus is also slightly larger, and lighter below and darker above. Vocalizations differ, but how they differ has never been published, and, in fact, it seems that there is a near total dearth of papers that deal with the potential split, which seems to be the main reason that SACC rejected it. Any graduate students out there looking for a project?
It appears that the scientific world has not yet caught up with the conventional wisdom of the world of birders in splitting the Pale-legged Hornero in at least two. The IOC and the AOU’s SACC have taken different approaches, with the IOC more forward-leaning and the AOU’s SACC more conservative, as normally seems to be the case. I can understand the arguments on both sides, but, like with the Green Jay / Inca Jay issue I looked at previously, it seems that AOU’s SACC likes leaving birds lumped, even if the evidence for a species being lumped is as limited or more limited then the existing evidence for a split.*** Then again, the opinions of checklist committees are perhaps not as valuable as the opinions of field guide authors, and in that respect, as with the IOC, the split has already occurred.
*Though as early as 1994’s The Birds of South America Volume II Ridgely and Tudor pointed out that cinnamomeus might be a separate species. In their Field Guide to the Songbirds of South America, published in 2009, Ridgely and Tudor come down fully on the side of the splitters because of the birds’ “differing morphology, voices, and disjunct populations.”
**All photos in this post are of Pacific Hornero Furnarius cinnamomeus and were taken in Ecuador in November 2010.
***And I would like again to emphasize that I am far from being competent to pass judgement on any of the far-more-knowledgeable-than-I people that populate the various and sundry committees that make checklist decisions. Seriously, I don’t know diddly.