Bulletin of The British Ornithologists' Club 2010 130(4):286-301
47499910

A new taxon of Collared Petrel Pterodroma brevipes from the Banks Islands, Vanuatu

Vincent Bretagnolle, Hadoram Shirihai
Vincent
Bretagnolle
&
Hadoram
Shirihai
293
Bull.
B.O.C.
2010
130(4)
brevipes.
We
follow
Watling's
(1986)
categorisation
of
colour
variation
in
P.
brevipes
(see
Fig.
1;
compare
also
Figs.
2,
4-12).
P.
b.
magnificens
immediately
recalls
dark-morph
P.
brevipes
on
Viti
Levu,
Kadavu
and
Gau
(Fiji),
or
from
southern
Vanuatu.
However,
in
plumage
P.
b.
magnificens
differs
from
the
latter
in
being
monomorphic
and
solely
occurring
in
a
dark
form.
During
December
2009
(see
Appendix
2),
all
of
the
180
P.
b.
magnificens
observed
were
dark.
Furthermore,
of
the
latter,
the
57
birds
observed
at
close
range
or
photographed
at
sea
were
categorised
ventrally
as
'dark
grey'
(Figs.
8-9)
or
'extreme
dark
grey'
(Figs.
10-12).
The
latter
two
accounted
for
c.90%
of
P.
b.
magnificens
off
the
Banks,
while
the
other
10%
were
only
slightly
paler
grey
ventrally
(Fig.
8).
In
contrast,
in
all
other
populations
of
P.
brevipes
dark
birds
represent
at
most
17%.
Being
solely
dark,
P.
b.
magnificens
completely
lacks
pale
plumage
types,
'pure
white'
and
'grey
peppering',
which
form
54-73%
of
brevipes
in
other
populations.
Type
'smoky',
which
could
be
considered
'midway'
in
the
spectrum
of
variation
is
also
absent
in
P.
b.
magnificens,
with
only
single
incidences
of
borderline
cases
between
'smoky'
and
'dark
grey'
(Table
2).
Furthermore,
the
dark
coloration
of
P.
b.
magnificens
is
on
average
even
darker
than
that
in
other
P.
brevipes
populations,
with
the
darkest
birds
('extreme
dark
grey')
comprising
c.40%
of
individuals
scored
in
the
Banks.
Such
birds
have
very
dark
underparts,
and
lack
or
have
very
faint
breast-bands,
and
the
very
dark
underwing
shows
only
small
white
areas
on
the
innerwing-coverts
and
the
larger
median
covert
row,
with
the
remaining
coverts
and
remiges
dark
grey
or
black.
The
nature
and
degree
of
differentiation
of
P.
b.
magnificens
versus
other
P.
brevipes
populations
is
at
the
same
or
a
higher
level
than
that
seen
in
several
other
closely
related
petrels.
Examples
include
the
scarcely
differentiated
three
taxa
that
comprise
the
P.
feae
complex
(Shirihai
et
ah
2010,
Gangloff
et
al.
in
prep.),
the
limited
plumage
differences
between
Vanuatu
and
White-necked
Petrels
(Imber
&
Tennyson
2001,
Shirihai
&
Bretagnolle
2010),
between
the
two
races
of
Gould's
Petrel,
P.
/.
caledonica
vs.
P.
/.
leucoptera
(Imber
&
Jenkins
1981)
and
between
Cook's
P.
cookii
and
Pycroft's
Petrels
P.
pycrofti
(Shirihai
2007).
Given
that
one
of
the
key
reasons
for
splitting
Collared
from
Gould's
Petrel
is
the
former's
dimorphic
coloration,
that
P.
b.
magnificens
is
monomorphic
acquires
even
greater
significance.
Breeding
locality
and
season.
In
Appendix
2,
we
detail
how
P.
b.
magnificens
was
discovered
to
be
presumably
breeding
on
Vanua
Lava
Island.
Although
we
did
not
observe
any
nests,
we
found
clear
evidence
of
breeding
there.
1.
Petrels
were
seen
coming
close
to
land
during
the
late
afternoon
/
evening,
when
they
seemed
to
'mill'
around
at
sea
below
the
island,
as
if
waiting
for
darkness
to
fly
inland.
2.
In
one
case
this
involved
a
displaying
pair
close
to
the
island.
3.
We
obtained
tape-recordings
of
display
calls
at
the
island's
summit.
These
calls
are
typical
calls
of
P.
leucoptera
/
brevipes,
and
included
flight
(titi)
as
well
as
ground
calls.
Indeed,
several
birds
were
heard
calling
from
the
ground,
both
early
at
night
and
prior
to
morning
departure.
The
relatively
large
number
of
sightings,
180
in
just
eight
days
at
sea,
in
the
Banks
suggests
that
P.
b.
magnificens
is
rather
abundant
locally.
It
could
also
breed
on
other
islands
in
the
Banks
with
similar
habitat,
especially
Santa
Maria
Island
(Gaua),
where
these
petrels
were
also
observed
(see
Appendix
2).
The
breeding
season
in
P.
b.
magnificens
seems
differentiated
from
other
populations
of
P.
brevipes
for
which
data
are
available,
although
at
this
stage
this
is
speculative.
Based
on
the
type
series
and
our
own
observations
(Appendix
2),
P.
b.
magnificens
breeds
either
in
the
austral
summer
or
slightly
earlier.
Many
that
we
saw
in
late
December
(if
not
most)
were
recent
fledglings
based
on
plumage
condition
(see,
e.g.,
Figs.
9
and
11),
although
it
seems
odd
that
recent
fledglings
should
remain
close
to
their
natal
island.
Birds
collected
in
late
January
had
enlarged
gonads,
which
suggests
either
a
rather
extended
breeding
period
or
that
the
breeding
season
is
actually
summer.
Totterman
(2009),
who
visited