Andrew-
One cannot draw the inference that because there were few bird remains in
fox scats, that foxes are not significant predators of birds. If the 4
remains cited all happened to be of something rare, such as a Night Parrot,
then predation at this low level might be highly significant. Further, scats
give only a partial indication of diet. Foxes are generally very partial to
eggs, yet egg remains will not show up in scats. For ground nesting birds,
foxes could have a significant impact by eating eggs only (something which
is entirely possible)and a scat analysis would give no indication of this.
The research you quote, and a great body of other research as well,
indicates that foxes switch prey readily. This means that the results of
fox diet investigations on one occasion or in one location cannot be used to
reliably predict what foxes will eat at other times, or under other
conditions. I think that until we have a lot more information, we would be
foolish to be too complacent about the predatory impacts of foxes.
Scott O'Keeffe
-----Original Message-----
From:
Behalf Of Andrew Taylor
Sent: 07 August 2001 00:16
To:
Subject: re: Bustards in south-west Victoria
On Mon, 6 Aug 2001, Lawrie Conole wrote:
> I agree that the evidence against the Fox in terms of being part of story
> about the disappearance of medium-sized ground nesting birds from large
> parts of southern Australia is not backed by hard facts. Though
> circumstancial, it's fairly convincing nonetheless. It occurs to me that
> the fairly healthy population of Bush Stone-curlews on fox-free Kangaroo
> Island in SA is a compelling piece of circumstancial evidence against
them.
I'm not sure the data for fox impact on Bush Stone-curlew is that much
more convincing, at least as I read HANZAB and the Action Plan, but
I can provide a counter-example anyway. The Magpie Goose is roughly
similar in size to Bustards and also subject to human predation. It is
presumably not subject to significant fox predation, but disappeared
from SE Australia with habitat destruction and human predation blamed.
I was curious if there were publications too recent to be in HANZAB and
did a quick search. I found a number of recent publications about the
impact of foxes on mammals but only one concerning birds: Read J. and
Bowen Z., "Population dynamics, diet and aspects of the biology of
feral cats and foxes in arid South Australia", Wildlife Research,
28(2):195-203, 2001. This is how they summarize results of their 10
year Roxby Downs study;
"When abundant, rabbits were the principal prey of both feral cats
and foxes. However, when rabbit numbers were low, the diets and
success of foxes and cats diverged considerably. While cats switched
to a wide variety of small vertebrates, foxes were forced to eat
mainly invertebrates, such as scorpions, grasshoppers, beetles and
centipedes. The small component of reptiles, birds and non-rabbit
mammals in the fox diet compared with that of the cat is consistent
with the findings of other studies (Bayly 1978; Catling 1988) and is
attributable to the species' different hunting styles. Foxes are appar-
ently less adept at stalking small vertebrate prey than are cats. As a
result, when rabbit density is low, foxes are opportunists and scavengers
(Martensz 1971; Bayly 1978) and feed extensively on invertebrates
(Catling 1988) and, in our study, slow fossorial reptiles."
They found birds in only 3 of 93 fox stomaches - one contained 2 Inland
Dotterels and two others containing individual unidentified birds.
Its possible birds vulnerable to foxes are absent/have been extirpated
from the study area - but this study certainly doesn't paint foxes as
significant bird predators. Perhaps fox diet in other area differs and
certainly there may be exceptions, species particularly vulnerable to
fox predation such as Malleefowl. Whether Bustards are in that category
though is another matter.
Incidentally, in 316 feral cat stomachs Read & Bowen found
these birds:
Zebra finch 9
Fairy-wren 9
Galah 2
Australasian grey teal 1
Crested pigeon 3
Budgerigah 1
Black-faced woodswallow 2
Mulga parrot 2
Richard's pipit 3
House sparrow 1
Crimson chat 2
Yellow-throated miner 3
Little button quail 1
Its conceivable foxes benefit some bird species by limiting cat numbers,
one recent study, Risbey DA. et al. "The impact of cats and foxes on the
small vertebrate fauna of Heirisson Prong, Western Australia" Wildlife
Research. 27(3):223-235, 2000, found feral cat numbers tripled after
fox numbers were reduced which had an adverse impact on small mammals
and reptiles - they didn't look at birds.
Andrew Taylor
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