Proposal (120) to South American Classification Committee
Elevate Spectacled Petrel Procellaria conspicillata to species rank
Effect on South American CL: this proposal would split the White-chinned Petrel, Procellaria aequinoctialis, into two species, P. aequinoctialis and P. conspicillata.
Background: The subspecies of Procellaria aequinoctialis (White-chinned Petrel) that breeds on Inaccessible Island, Tristan da Cunha in the Atlantic Ocean, P. a. conspicillata, has been treated at the subspecies rank during this century by Peters (1931), Meyer de Schauensee (1966, 1970), Blake (1977), Sibley and Monroe (1990), and Handbook of the Birds of the World Vol. 1. On the other hand, Shirihai (2002: A complete Guide to Antarctic Wildlife) treats this taxon as a species, as does the literature on long-line fishing etc.
The taxon conspicillata differs dramatically from aequinoctialis by the striking white U-shaped facial markings. It is also the only population of aequinoctialis that breeds north of the Sub-Antarctic Convergence. Seabirds are very sensitive to water temperatures, and biogeographically water temperature changes (such as convergences) appear to function in the same way as physical barriers such as mountains for landbirds. In other words, the fact that this is the only form breeding north of the convergence is probably quite relevant to the question of gene flow with other forms.
New information: Ryan (1998. The taxonomic and conservation status of the Spectacled Petrel Procellaria conspicillata. Bird Conservation International 8: 223-235) provided data on vocalizations that showed that conspicillata differed significantly from aequinoctialis both in its groan calls and rattle calls. These differences were mainly in call structure (one part versus two part calls), frequency, note length, and call rate. Playback experiments were conducted on conspicillata, and they showed a significant difference in response to conspicillata versus aequinoctialis calls, responding to the former and not the latter. Vocal differences appear to be important to species recognition and mate formation in procellariids. Vocal differences between other members of the genus Procellaria (aequinoctialis and parkinsoni) have been used to make taxonomic inferences (Warham 1988; Notornis 35: 169-183, Warham 1996; The behavior, population biology and physiology of the petrels. Academic Press). Ryan also gives information suggestive that conspicillata is smaller than aequinoctialis. As well, conspicillata breeds marginally earlier in the season (probably 4 weeks or so) than aequinoctialis. The nearest colonies of aequinoctialis are in South Georgia, I don't have a way to calculate distances but the gap is probably at least 1000 km. There appear to be many potential barriers to gene flow between aequinoctialis and conspicillata.
Recommendation: The sample sizes are not all that impressive in Ryan's work. However, the vocal differences noted and illustrated in tables and sonograms appear to be very distinct. I have no reason to suspect that more complete sampling would alter the conclusions. Voice in Procellariiformes appears to be a useful taxonomic feature. These colonial seabirds are not strongly territorial and voice seems to serve in species recognition and mate acquisition. Also note that in many species, and I don't know if this applies to conspicillata, nesting island visits are conducted at night when vocal differences are more important than visual features. Even so conspicillata differs strongly visually from aequinoctialis, which is circumpolar and rather uniform in appearance. Procellariform plumage patterns tend to be conservative. I think that the differences noted, and particularly the playback experiments are quite convincing in that two species level taxa are involved. I propose a yes vote to split conspicillata (Spectacled Petrel) from aequinoctialis (White-chinned Petrel).
Note: I do recall that conspicillata has been observed off the Atlantic coasts of South America, but we will have to make sure that this is indeed the case. I recall that they have been detected as by catch by fisheries off the coast of Brazil.
Alvaro Jaramillo, April 2004
Comments from Zimmer: "YES. The morphological and vocal differences appear to be significant, and the distributional situation appears to preclude gene exchange. I think this is long overdue."
Comments from Stotz: "YES. [Conspicillata apparently winters primarily at sea off S. Brazil. There are photos and specimens (Olmos 1995, 1997, 2000), including at least one from the São Paulo coast.]"
Comments from Stiles: "YES. The published evidence for a split is much stronger than that for maintaining these two forms conspecific."
Comments from Robbins: "Yes, published information indicates that conspicillata should be considered a species."
Comments from Nores: "SI, las diferencias de color en la cabeza, que además de la U señalada por Jaramillo está la frente blanca (según P. Harrison 1983), son enormes para un género con poca variación entre las especies. Además, el hecho que nidifique al norte de la Convergencia Subantartica y que tenga diferencias en vocalizaciones, son importantes aspectos para separarlos."