I have just returned from the 1st Leg of Geoscience Australia's current marine
surveys off the West Australian coast and thought I would write up a brief(ish)
note on some of the seabird observations during the trip.
We boarded the RF Sonne (a German research vessel) in Singapore and were lucky
enough to make passage through the Sunda Strait and thus past Anak Krakatau
(Child-of-Krakatoa) which has rebuilt as a low cone on top of the original
volcano. This was obviously a great highlight for a boat load of geologists!
We sailed on towards Christmas Island, where we had to complete some
bathymetric mapping along the east coast of the Island. Unfortunately we
completed this in one night and thus never saw the Island in daylight! Just as
well as my wife had commented that I wasn't allowed to return to Christmas
Island without her, having spent our honeymoon there only 10 months ago.
However, as we approached from the north we saw most of the local breeding
seabirds including Abbotts, Red-footed and Brown Boobies, and White-tailed
Tropicbirds (Golden Bosunbird) but surprisingly no Frigatebirds which were
either flying too high to be easily noticeable or were sticking closer to the
island. The Red-footed and Abbott's Boobies were first observed over the Javan
Trench (~6500m water depth where we crossed it) about 100km south of Java.
Red-footed Boobies were the most commonly observed seabird from this point
until several hundred kilometres SE of Christmas Island. However, Abbott's
Boobies were never common and were only observed to the north of the island but
this is probably coincidental. I know it has previously been suggested that
Abbott's Boobies may feed in the vicinity of the Java Trench but I believe that
radio-tracking of some individuals showed that most stayed closer to the island.
As we moved SE of Christmas Island, several Bulwer's Petrels were observed
(including one still in Australian waters) and the numbers of Wedge-tailed
Shearwaters also started to increase. The dip of the trip also occurred inside
Australian waters as an all-dark petrel past the ship too quickly and just too
distantly to be nailed down. It flew more strongly and directly than the
Bulwer's Petrel, though still flapping regularly in the weak winds and was
noticeably more robust/larger. It was quite long, narrow-winged and long-tailed
with a featureless dark brown plumage. It was most likely a Jouanin's Petrel
but I couldn't rule out other (admittedly less likely) species.
As we approached the Wallaby Plateau – a vast area of sea-floor, 400km W of
Geraldton, that although deepwater is still raised above the surrounding
abyssal plains (4500m water depth) – we started to see the first Great-winged
Petrels (nominate race) of the trip. These petrels were to be amongst the
commonest birds for the next 3 weeks as we ran many survey lines parallel to
the shelf slope (from 200m to 4500m water depth). By far the best areas for
seabirds were in moderate to deep waters (800-4000m) within the canyon systems
that run perpendicular to the shelf edge. These canyons play a role in sediment
transfer from the slope to deeper waters but are clearly also important feeding
areas for the seabirds in this region. There were commonly large mixed feeding
flocks of Wedge-tailed Shearwaters, Lesser Noddies, and Bridled and Sooty Terns
that often numbered several hundred birds. These species were to be expected as
we spent a lot time working in the Murchison Canyon immediately to the west of
the Abrolhos Islands. Great-winged Petrels and Little Shearwaters were also
noticeably more abundant above these canyon systems, as were the irregular
sightings of Wilsons and White-faced Storm-petrels.
Little Shearwaters were observed almost daily along the whole coastline but it
was not unusual to see upwards of a hundred an hour above the Murchison and
other nearby canyons. Of great interest to me was that I observed 7-8 'Little'
Shearwaters with apparently darker heads and a thick, dark trailing edge to the
underwing. These birds were immediately obvious as the underwings of the vast
majority of Little Shearwaters here had brilliant white underwings. I am unsure
what to make of these birds and unfortunately did not manage even a bad photo
of any of them. I guess it is most likely a feature of wear or age that has not
been noted (or at least I am unaware of) so thought it worth mentioning here.
In fact photographing any of the birds was actually very difficult from such a
large vessel as the birds even if just off the bow would still be a minimum of
20 or 30 metres away and usually a lot more.
The bird of the trip was also seen off the Murchison Canyon, as I was treated
to good but brief views of a passing GREAT SHEARWATER. As vagrant aussie
seabirds go it is quite an easy bird to id but was still an extremely exciting
Aussie lifer for me and certainly not a bird I had expected to see on this
trip. This location isn’t too surprising a place to find this vagrant in
Australia but mid-November certainly breaks the Feb-April pattern of previous
reports (if a very few records constitutes a pattern). By mid-November most
birds should have returned to their breeding islands in the south Atlantic,
after completing a clockwise, trans-equatorial migration of the Atlantic. It
would be pure guess work to suggest a reason for a bird to be off the WA coast
now – maybe an early returned breeder that had drifted further west on a
feeding loop than normal or a lost/disrupted 2nd year/non-breeding bird.
Overall the diversity of birds along off WA coast (from 100km NW of Rottnest to
directly west of Dirk Hartog Island) was very low and the number of cetacean
sightings was extremely poor (possibly we were in deeper waters than is optimal
for increased sightings) but it was still a thoroughly enjoyable trip.
Sorry this supposedly brief report has ended up so quite long.
Cheers Dan
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