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
Birding-Aus is on the Web at
www.shc.melb.catholic.edu.au/home/birding/index.html
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