Proposal (1001) to South American Classification Committee

Treat Eudyptes filholi as a separate species from E. chrysocome

Note:: This is one of several situations that the IOU Working Group on Avian Checklists has asked us to review. I have no first-hand knowledge of this situation, so my goal here is to lay out the critical facts of potential relevance to taxonomy just to get the discussion started. I hesitated to do this one, because the potential new species is extralimital, and also because the post-retirement pruning of my library has reduced the number of independent references I can check..

Effect on SACC: Passage of this proposal would not affect current SACC classification in any way except by constricting the range of what we treat as Eudyptes chrysocome.

Background: Our current SACC note is as follows (which I need to update to include Frugone et al. (2021):

8. Jouventin (1982), Jouventin et al. (2006), and Banks et al. (2006) demonstrated that moseleyi, traditionally treated as a subspecies of E. chrysocome, differs in voice and mating signals from, and is moderately differentiated genetically from, chrysocome. SACC proposal passed to treat moseleyi as a separate species. For English names for this species pair, see SACC Proposal 516. The two species were called “Northern Rockhopper Penguin” (moseleyi) and “Southern Rockhopper Penguin” (chrysocome) in Dickinson & Remsen (2013) and del Hoyo & Collar (2014). For additional support for treatment as separate species, see Mays et al. (2019).

Eudyptes moseleyi is a vagrant to the SACC region based on occurrences in the Falklands/Malvinas, and a 2019 record on the coast of Rio Negro (northern Patagonia), Argentina (fide Mark Pearman); it breeds on islands in the Southern Oceans, e.g. Tristan da Cunha, Gough, St. Paul, Amsterdam). Eudyptes chrysocome breeds on the Falklands/Malvinas and islands off S. Chile. The taxon filholi Hutton, 1879, is currently treated (e.g. Dickinson & Remsen 2013, del Hoyo & Collar 2016, IOC, Clements) as a subspecies of E. chrysocome. It breeds on several island groups (e.g., Crozet, Kerguelen, Heard, Macquarie, Auckland) in mainly subantarctic waters in the southern Indian Ocean and off Australia-New Zealand, i.e., on the other side of the planet from nominate chrysocome; however, despite that distance and gap in breeding distribution, it differs only in minor phenotypic characters from nominate chrysocome, primarily in having the narrow lower margin of the mandible pale fleshy pink instead of orangey like the rest of the bill. Below are photos from Macaulay Library; see also photos in Howell and Zufelt (2019):

Eudyptes c. chrysocome, Falklands/Malvinas, by David and Kathy Cook (ML 205735341, flipped and slightly cropped):

Eudyptes c. filholi, Heard and McDonald Iss., by Robert Tizard (ML343435611 slightly cropped):

For comparison, here is Eudyptes moseleyi, with its considerably more flamboyant plumes, a returning vagrant to the Falklands/Malvinas, by Alan Henry (ML 186628281). Of interest is that Alan Henry noted that this bird was “Returning bird first seen in 2014. Paired with Southern Rockhopper Penguin, sitting on single egg” https://ebird.org/checklist/S61273479 and the same list reports hybridization there with Macaroni Penguin (E. chrysolophus). EBird, by the way, calls this “Moseley’s Rockhopper Penguin” not Northern Rockhopper Penguin.

New information: Frugone et al. (2021) through a sophisticated genetic analysis showed that all three taxa represented separate lineages, whereas the different island populations sampled within each taxon did not. Note that genetic distance roughly corresponds to degree of plumage differentiation, with Eudyptes chrysolophus (Macaroni Penguin) sister to the other three, and filholi and nominate chrysocome the least differentiated genetically.

The “species delimitation” analysis that the authors used implicitly delimits species under the General Lineage Species Concept, not the BSC. Note that under this method of “species” delimitation any degree of differentiation of allopatric taxa would find them to be “species.”

“In summary, at the molecular level, several lines of evidence support recognition of three species of rockhopper penguins: 1) genomic differentiation among E. moseleyi, E. chrysocome and E. filholi substantially exceeds differentiation observed within each taxon; 2) there is no genomic evidence of admixture or hybrid individuals among these taxa; 3) our analyses suggest no contemporary gene flow among the three taxa; and 4) species delimitation analyses strongly support a three-species designation to the exclusion of a model designating E. chrysocome/E. filholi as conspecific. Our results, thus, confirm the findings of previous studies revealing reciprocal monophyly with mtDNA markers, supporting this three-species designation (Banks et al., 2006; Cole, Dutoit, et al., 2019; Cole, Ksepka, et al., 2019; de Dinechin et al., 2009; Frugone et al., 2018; Mays et al., 2019).”

The authors are quite aware of this issue and go on to discuss factors relevant to BSC criteria, e.g. voice and display. They noted that whereas moseleyi is known to have different vocalizations from the other two, no such differences are known between nominate chrysocome and filholi. With respect to filholi:

“ … whereas the main morphological differentiation between the sub-Antarctic taxa corresponds to a more pronounced pink to white gape (bare skin around the bill) on E. filholi which is black on E. chrysocome (Tennyson & Miskelly, 1989). Other morphological features differentiating E. filholi from E. chrysocome include a narrower bill and the shape of the black mark on the undersurface of the apex of the wing (Hutton, 1879). Finally, vocalizations are an important behavioural trait in penguins, since they may rely more strongly on auditory cues for mate selection and individual recognition than on morphological characters (Aubin & Jouventin, 2002; Jouventin et al., 2006; Searby & Jouventin, 2005). Differences have been found in the mating calls of E. moseleyi in comparison with those of E. chrysocome (when considered a single species to E. filholi), providing an additional line of evidence for delimiting those taxa (Jouventin et al., 2006). However, as far as we know, vocalizations of E. chrysocome and E. filholi have not been directly compared and should be a priority for future data collection and study.”

Discussion and recommendation: In my view, this boils down to philosophy and species concepts. Three distinct lineages are involved. The split between moseleyi and chrysocome+filholi is marked by vocal differences and reasonably dramatic plumage differences from which we can infer, for better or worse, that they have diverged to the point that free gene flow would no longer be possible. That vagrant moseleyi can pair with and at least produce eggs with Falklands chrysocome is not evidence for free gene flow. That filholi and chrysocome have not diverged to the point of developing differences in characters considered to be important in penguin mate selection means that under the BSC, they are best considered subspecies of the same species. Further field research on that should be encouraged, as suggested by the authors, and should be straightforward. If these penguin colonies are visited to census them and gather blood samples, then why doesn’t someone do some recording of vocalizations?

Frugone et al. (2021) advocated for species rank in part to aid conservation measures. Emotionally, I am sympathetic to this, but objectively, I urge extreme caution in letting this influence a scientific decision. Otherwise, we and others making such taxonomic decisions will undermine our credibility and make ourselves vulnerable to accusations of advocacy, a point made by anti-environmental groups.

All in all, I recommend a NO on this one, especially since additional evidence would seem so readily obtainable given that these remote islands are indeed visited by penguin biologists. If recordings of vocal display reveal substantial differences, then that would change my vote immediately to a YES.

English names: Frugone et al. (2021) used “Northern Rockhopper Penguin” and “Southern Rockhopper Penguin” as in SACC and elsewhere, and use “Eastern Rockhopper Penguin” for filholi. If the proposal passes, I think we need a separate proposal on English names. Keep in mind, as Mark Pearman just reminded me, that we voted to avoid those longer names by going with “Tristan Penguin” for moseleyi and retain “Rockhopper Penguin” for the more widely distributed and more familiar chrysocome s.s. (SACC 516).

References (see SACC Bibliography for standard references)

Frugone MJ, TL Cole, ME López et al. 2021. Taxonomy based on limited genomic markers may underestimate species diversity of rockhopper penguins and threaten their conservation. Diversity and Distributions. 27: 2277–2296.

Howell, S. N. G., and K. Zufelt, 2019. Oceanic Birds of the World. A Photo Guide. Princeton University Press.

Van Remsen, June 2024

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Comments from Stiles: “Again, NO until data on the vocalizations and mating displays of filholi become available.”

Comments from Areta: “NO. This was my WGAC vote, which I repeat here: " I vote NO to the split of filholi. To me, this study has shown evidence on the validity of filholi as a subspecific taxon. The case is quite borderline from my perspective. The authors are careful regarding the meaning of their work, even when they endorse the split. I´d rather wait for evidence regarding vocalizations. The degree of genetic differentiation is on the lower end of the genus. I am happy with the conservative stance here, although I acknowledge that the split might be seen with good eyes by others."

Comments from Claramunt: “YES. A difficult borderline case. I base my decision on the fact that these penguins show facial differences that are not only diagnostic, but that can play a role in species recognition. The light margin at the base of the bill in filholi is distinctive.”

Comments from Robbins: “NO. This is indeed borderline on whether to recognize as filholi as a species. I’m fine waiting until the vocal data are obtained that might turn this into a straightforward decision. So, for now NO.”

Comments from Jaramillo: “YES – I am with Santiago on this one, apart from plumes facial features and particularly pink skin around bill differs in species of penguins. Spheniscus for example are readily identifiable on pink skin distribution, in addition to how many dark bands they have on the breast. It is a borderline case, but these lineages are separate, and vagrant penguins do happen, actually quite regularly. I gather that the genetic work did not find any possible gene flow, so that is important.”

Comments from Pearman (voting for Remsen): “NO. I’m not impressed by vocal differences between recordings of chrysocome and filholi that I have listened to, which is in contrast to the radically different moseleyi vocalizations. I also note that several authors urge caution over the field identification of filholi from chrysocome due to variation in the thickness of the supercilium and extension of head plumes. Adding to this, the recently published marginal genetic divergence tips the scales towards maintaining subspecific status for filholi under the BSC. 

Comments from Louis Bevier (voting for Bonaccorso): “NO. While the single morphological character separating filholi and chrysocome, pink gape and stripe along bottom of mandible in filholi, is rather distinctive and may be important, a quick comparison of vocalizations suggests to me that filholi and chrysocome are rather similar, especially compared to moseleyi (Northern) and why that previous split was well-supported. Thus, I agree with others that analysis of vocalizations and associated behaviors is needed before we can make a decision in this case.

“I had fun listening to squawks and brays and barks for the three taxa. Ted Parker has a two long, good cuts from the Falklands of chrysocome, including a point where he says, "duetting birds." With that as a baseline, I compared a few recordings of filholi (Doug Gochfeld has some and my Birds of New Zealand app has one recording) and moseleyi (one recording on xeno-canto of birds said to be squabbling, so not the same courtship context). To me, filholi and chrysocome are similar, whereas moseleyi is clearly different (deeper and lower), which we already knew. Given this, I would need to see how Jouventin et al. analyzed the vocalizations and associated behaviors to get a sense of whether those characters will prove helpful. A cursory listen suggests filholi and chrysocome might not differ that much, but clearly someone needs to do the analysis in a rigorous way and compare behavior of courting birds.

“I also skimmed through the genetics papers, Frugone et al. (2021) and Mays et al. (2019). Mays et al. said there is admixture between filholi and chrysocome, but Frugone et al. said they found none and argue that the Mays et al.'s dataset was underpowered and could not evaluate species boundaries. So while species concepts may be one aspect of the differing conclusions, Frugone et al. 3 species and Mays et al. 2 species, there appears to be differences in genetic data and analyses.

Mays, H. L., D. A. Oehler, K. W. Morrison, A. E. Morales, A. Lycans, J. Perdue, et al. 2019. Phylogeography, population structure, and species delimitation in rockhopper penguins (Eudyptes chrysocome and Eudyptes moseleyi). The Journal of Heredity, 110(7):801–817. https://doi.org/10.1093/ jhered/esz051”

Comments from Lane: “NO, as per the comments by other committee members above.”