Proposal (#120) to South American Check-list 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 Cuhna 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 longline 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 Subantarctic 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 procellarids. 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 behaviour,
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
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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 estre las especies. Además, el hecho que nidifique al norte de la Convergencia Subantartica y que tenga diferencias en vocalizaciones, son importantes aspectos para separarlos."