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."