Proposal (1074) to South American Classification Committee

Elevate Butorides sundevalli to species rank

Effect on South American CL: This proposal would elevate the Lava Heron, Butorides sundevalli, from a subspecies of the Striated Heron (B. striata) to full species rank.

Background: The Lava Heron was first described by Sundevall (1871) as Ardea plumbea, renamed Ardea sundevalli by Reichenow (1877) to avoid nomenclatural conflict, and placed in Butorides by Sclater and Salvin (1870). The taxon was placed in the genus Butorides by Sclater and Salvin (1870), where it has remained to this day. It was treated as a full species through much of the twentieth century (Peters 1931), until Martínez-Vilata and Motis (1992) reassigned it as a subspecies of the Striated Heron (Butorides striata). In 2002, the South American Checklist Committee reviewed the available morphological evidence and, in the absence of genetic data, declined to make a formal decision on the taxonomic status of sundevalli (Remsen 2002). That taxonomic uncertainty has now been resolved by new molecular and morphometric data; Mendales et al. (2026) in Molecular Phylogenetics and Evolution.

New information: Mendales et al. (2026), present a phylogenomic analysis based on ultraconserved elements (UCEs) demonstrating that Galápagos Butorides are genetically distinct from South American Striated Heron and more closely related to the Green Heron (B. virescens) of North and Central America. In this same publication, the authors showed that Lava Herons are diagnosable from all other Butorides by significantly larger bill dimensions measured from both live individuals and museum specimens. Culmen height ranges from 12.13–15.46 mm (mean = 13.12, n = 20) versus 9.51–12.43 mm (mean = 10.97, n = 23) in South American Striated Heron; culmen width averages 9.39 mm versus 8.31 mm. These bill differences are consistent across plumage morph/categories in Lava Herons, consistently showing robust bill morphology that distinguishes them from mainland Butorides populations [i.e., five categories described by Kushlan (2009) based on the side of the neck and coloration under parts: 1) black/back to dark grey; 2) dark grey/dark grey; 3) dark grey/light grey; 4) grey/grey, and 5) light grey/grey brown to rufous]. One light-plumaged category-5 individual captured on the Galápagos, externally indistinguishable from mainland Striated Heron, fell within the Lava Heron range for both culmen height and width, and was placed firmly within the Lava Heron clade by UCE phylogenetic analysis. This category-5 individual encapsulates the central finding of this study: plumage and phylogenetic affinity are decoupled in Galápagos Butorides. A bird that would historically have been identified as B. striata on appearance alone is, by every molecular and morphometric criterion, a Lava Heron, supporting the conclusion that all Butorides on the Galápagos, regardless of plumage morph, belong to a single endemic species, supporting Hayes' (2002) observation that "B. striatus may not even occur in the Galápagos."

One potential objection concerns mitonuclear discordance, whereby mitogenome data place the Lava Heron sister to South American Striated Heron rather than to B. virescens as recovered by nuclear UCEs. This likely reflects mitochondrial capture rather than true phylogenetic affinity, as presented by Mendales et al (2026), and thus, whole-genome data will be necessary to fully resolve the history of introgression and incomplete lineage sorting in this group. Importantly, thousands of nuclear loci show minimal discordance and consistently support Lava Heron as distinct from B. striata.

Recommendation: I favor following Mendales et al. (2026) and elevating Butorides sundevalli to full species rank for the following reasons. 1) The nuclear phylogenomic evidence is unambiguous: the Lava Heron is recovered as monophyletic across all sampled individuals regardless of plumage type, is more closely related to the Green Heron than to the Striated Heron and cannot be correctly placed as a subspecies of B. striata under any species concept that requires monophyly. 2) The morphometric evidence provides an independently diagnosable character (e.g., bill dimensions) that distinguishes sundevalli from all other Butorides taxa across its full geographic range and across both plumage morphs. 3) The current subspecies treatment is not supported by any published molecular data and was itself adopted without formal justification (Martínez-Vilata and Motis 1992). 4) Retaining sundevalli within B. striata would require either accepting a paraphyletic B. striata or collapsing B. virescens into it as well, neither of which is defensible under current evidence.

English names: The name "Lava Heron" is well established in the literature (Kushlan and Hancock 2005; HBW), widely used by field ornithologists and researchers working in the Galápagos, and accurately reflects both the species' foraging substrate, its distinctive coloration, and a natural association with the Galápagos as volcanic islands. "Striated Heron" is retained for South American B. striata sensu stricto, consistent with current usage (Clements et al. 2025). Because the Lava Heron and Striated Heron are not sister species, there is no compelling reason to impose compound names linking the two. I therefore propose retaining "Lava Heron" for B. sundevalli and "Striated Heron" for B. striata, with the understanding that the split is supported by different biogeographic, morphological, and phylogenetic histories.

References:

HAYES, F. E. 2002. Geographic variation, hybridization, and taxonomy of New World Butorides herons. North American Birds 56: 4–10.

Kushlan and Hancock. 2005. The Herons. Oxford University Press.

MARTÍNEZ-VILATA, A., AND A. MOTIS. 1992. Family Ardeidae (herons). Pp. 376-429 in "Handbook of the Birds of the World, Vol. 1. Ostrich to ducks." (J. del Hoyo et al., eds.). Lynx Edicions, Barcelona.

MENDALES, E. Z., J. E. McCORMACK, J. S. CEPEDA, J. P. DUMBACHER, AND J. A. CHAVES. 2026. Global phylogenetic relationships of Butorides herons (Aves: Ardeidae) reveal the evolutionary history and taxonomic status of the Galapagos Lava Heron. Molecular Phylogenetics Evolution 220: 108600.

Jaime A. Chaves, May 2026

Vote tracking chart:

https://www.museum.lsu.edu/~Remsen/SACCPropChart1044+.htm

Comments from Stiles: “YES on recognizing B. sundevalli as a separate species. This is solidly supported by multiple lines of evidence, including phylogenetics, biogeography, morphology and ecology, as well as putting the taxonomy of Butorides on a more solid basis.”

Comments from Remsen: “YES. Multiple lines of evidence, as outlined in this proposal, make treatment as a separate species the most suitable, if not the only acceptable, taxonomic treatment.”

Comments from Lane: “YES. This taxonomic issue has been mentioned in gray literature for at least a decade or more suggesting that Lava Heron has two color morphs, and that the morphology is more important than plumage color in separating it from mainland Butorides. To me, this makes the split seems pretty solid. I do wonder if mainland South American Striated Herons should retain that name in light of the phylogenetic relationships within the genus, suggesting that New World birds are closer to one another than the “Striated” group is across the Old World tropics. If Afrotropical and Australasian taxa are split from B. striatus (as it appears they should be), shouldn’t we retire “Striated Heron” in favor of a name only to be applied to South American birds in accordance with our general name policy under such circumstances? But this proposal doesn't suggest that split, so I suppose this comment should be brought up when that split is placed before SACC.”

Comments from Robbins: “YES to recognizing Butorides sundevalli as a species based on several reasons provided in the proposal.”