Three recent records of Pied Cormorant (Phalacrocorax varius) predation on Silver Gull chicks (Larus novaehollandiae) in Western Australia

3 Pages·2003·0.66 MB·English

by  C R Lamont

THREE RECENT RECORDS OF PIED CORMORANT
(PHALACROCORAX VARIUS) PREDATION ON SILVER
GULL CHICKS (LARUS NOVAEHOLLANDIAE) IN
WESTERN AUSTRALIA
By C.R. LAMONT
Division of Science and Engineering, School of Biology
Murdoch University, South St Murdoch WA 6150
ABSTRACT
Pied Cormorants (Phalacrocorax varius) have been recorded
throughout coastal areas and inland waters of Australia
eating a variety of fish and a few crustacean species using
pursuit-diving. This paper records three isolated events
where Pied Cormorants were observed eating live Silver
Gull (Lams novaehollandiae) chicks or attempting to remove
chicks from gull nests on Penguin Island, Western Australia.
INTRODUCTION initiated clutches (Dunlop 1986),
with peaks becoming pro¬
Penguin Island is a coastal
gressively less synchronised
limestone island situated 42
throughout the protracted season
kilometres south-west of Perth,
(Wooller and Dunlop 1979). There
W.A., and 600m west of Mersey
is a pronounced peak in fledglings
Point in Shoalwater Bay, Shire of
in early June (Dunlop et al. 1988).
Rockingham (Dunlop et ai 1988).
Pied Cormorants roost on the Pied Cormorants are underwater
eastern side of the northern most pursuit-divers that use their feet
point of the island between to reach the bottom where they
February and July. Silver Gulls search for their prey (Schreiber
nest on the southern and and Clapp 1987). At various sites
northern plateau of Penguin within Western Australia,
Island. Laying usually begins in Victoria, South Australia and New
late March, early April and Zealand, Pied Cormorants have
continues until November. Their been reported eating a variety of
laying pattern is consistently fish and crustacean species all
trimodal with peaks in autumn taken by diving, using their feet
(April), winter (June) and spring for propulsion (for review see
(August-September). The main Marchant and Higgins 1990). A
laying peaks are followed by a Western Australian study found
pronounced trough in newly the feeding pattern of three
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common cormorant species, the made to take chicks by reaching
Little Pied (P. melanoleucos), Little into the gull’s nests. Defence by
Black (P. sulcirostris) and the Pied the gulls was apparently too
Cormorant to be opportunistic strong on this occasion and the
but restricted to a variety of slow- cormorant flew from the colony
swimming benthic-feeding fish without success. Again, only those
and crustaceans (Trayler et ai gulls from directly adjacent nests
1989). An early paper (Storr 1965), attempted any form of defence
on the birds of Rottnest Island in against the cormorant.
Western Australia reported the
possibility of Pied Cormorants Record No. 3
taking the ducklings of the
On 28 September 2000, a Pied
Australian Shelduck (Tadorna Cormorant was observed flying
tadornoides), although this was not over the gull colony at the
actually observed. northern end of the southern
plateau. The cormorant made
several low passes before landing
OBSERVATIONS and removing a gull chick. The
chick was held in the cormorant’s
Record No. 1
beak while it flew over the water
On 25 May 2000, a single Pied
and was then swallowed whole
Cormorant was seen walking into
once the cormorant had landed
the Silver Gull breeding colony
on the water. The gulls responded
on the southern plateau of
by aerial attacks on the
Penguin Island. It approached a
cormorant, continuing while the
nest within 10m of the rocks
cormorant flew over the water
where it had previously perched
and only ceased once the chick
and removed a single gull chick.
was eaten. The gulls appeared to
The cormorant held the chick in
be making attempts to snatch the
its beak while it moved about 2m
chick off the cormorant in the
away from the nest, then same way that they would attack
swallowed the chick whole. This
another gull carrying a large piece
action was repeated with a second
of food.
chick from the same nest. The
In the past, Pied Cormorants have
cormorant then flew away from
been observed roosting on
the area. During the cormorant’s
Penguin Island and approxi¬
attack, only nearby gulls
mately 400-500 pairs have nested
attempted to defend their nests,
on Shag Rock, 600m north of the
using aerial dive-bombing and
island (Dunlop et al. 1988).
vocalisations.
Although no recent estimates of
population size have been made,
Record No. 2
cormorants have been recorded
On 30 May 2000, a single Pied nesting and successfully raising
Cormorant entered the gull chicks on Penguin Island since at
colony on the southern plateau of least 1999 (personal observation).
the island. As it walked amongst The breeding season of the Pied
the nests, several attempts were Cormorant in this region extends
136
from February to July, coinciding MARCHANT, S. and HIGGINS, R.J.
with the first two observations of 1990. Handbook of Australian and
predation on gull chicks during New Zealand Birds. Volume 1 Ratites
May. The third observation, in to Ducks., Oxford University Press,
September, did not however Melbourne.
coincide with the cormorant's
SCHREIBER, R.W. and CLAPP, R.B.
breeding season.
1987. In: Seabirds: Pelecaniforme
feeding ecology (Ed, Croxall, J.P.)
Cambridge University Press,
ACKNOWLEDGEMENTS
Cambridge, pp. 173-188.
Stuart Bradley and Ron Wooller
STORR, G.M. 1965. The Avifauna
kindly provided comments on a
of Rottnest Island, Western
draft of this paper.
Australia II. Lake and Littoral
Birds. Emu, 64: 48-60.
REFERENCES TRAYLER, K.M., BROTHERS. D.J.,
WOOLLER, R.D. and POTTER, I.C.
DUNLOP, J.N. 1986.The comparative
1989. Opportunistic foraging by
breeding biology of the sympatric
three species of cormorants in an
Crested Tern Sterna bergii
Australian estuary. Journal of
(Lichtenstein) and Silver Gull Larus
Zoology, London, 218: 87-98.
novaehollandiae (Stephens) in south-
western Australia. PhD Thesis, WOOLLER, R.D. and DUNLOP,
Murdoch University, Perth, J.N. 1979. Multiple laying by the
Western Australia. Silver Gull, Larus novaehollandiae
Stephens, on Carnac Island,
DUNLOP, J.N., KLOMP, N.I. and
Western Australia. Australian
WOOLLER, R.D. 1988. Penguin
Wildlife Research, 6: 325-35.
Island, Shoalwater Bay, Western
Australia. Corella, 12:93-98.
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