-- I read with interest the comments of Rod Gardner & PJ Milburn regarding the
identification of Giant Petrels. The two sibling species were only separated
in 1966
after some research carried out at Macquarie Is by Bourne & Warham (1966).
Identification of the two species is thought to be quite strait forward, those
with a
dark reddish tinge to the unguis (Bill tip) Northern GP (Red for north where it
is
warm). Green Bill tip Southern GP (Green for south where it is cooler).
It is our experience here at Wollongong that the vast majority of GPs that
occur here
and along the NSW coast are (birds of the year) Juveniles, therefore Bill
coloration may
not be fully developed making specific identification of some individuals at
sea very
difficult/if not impossible even in the hand. In such cases these birds are
best
described as Macronectes Sp.
The problem of specific identification does not however end here. At several
breeding
stations throughout the Sub-Antarctic the two sibling species breed
sympatrically and a
small number of inter-specific pairs occur.
At Bird Island South Georgia (South Atlantic) inter-specific pairs represent
1.5 percent
of the population. Inter-specific pairings were of two distinct types. In Type
A, a male
M.giganteus was paired to a female M.halli: In Type B, a male M.giganteus was
paired to
a female bird that could not be identified using bill colour. These birds had
bills
that were a weak horn colour throughout, lacking the dark red tip of M.halli or
the pale
green tip of M.giganteus.
All six chicks of type A pairs fledged successfully; four of the nine chicks
from type B
pairs fledged successfully. All of these chicks showed the plumage
characteristic of
both M.halli and M. giganteus fledglings, but had a bill rather paler and less
yellowish
than M.halli chicks and lacking both the reddish tip that some show and the
green tip of
M.giganteus chicks.(Hunter 1982 EMU 82 supplement).
As though this is not confusing enough, the Giant Petrels breeding on Gough
Island in
the Atlantic Ocean show characteristics of both M.giganteus and M.halli. Some
studies
suggest that a third species may exist (Voisin & Bester 1981). These birds
have green
bill tips as in M.giganteus and a breeding biology similar to that of M.halli.
Banding studies and recoveries indicate that GPs from many different breeding
stations
throughout the Sub-Antarctic occur in Australian seas particularly on the east
coast of
Australia.
Our own studies here at Wollongong clearly indicate that the Northern Giant
Petrel
M.halli is more abundant in NSW waters than the NSW Rarities Committee would
have us
believe!! Recent studies at several breeding stations indicate that the NGP
may
actually be increasing in numbers.
Cheers :-))
Lindsay Smith
--
SOSSA "Wildlife Research" H.Q - Wollongong
Southern Oceans Seabird Study Association Inc
Lindsay E. Smith & Janice G. Jenkin-Smith
Janice G. Jenkin.JP.,CMC. Civil Marriage Celebrant
P.O. Box 142, Unanderra NSW Australia 2526
Phone +61 (02) 4271 6004
Fax +61 (02) 4272 4626
Mobile 0418 603 007
Email:
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