Sadly these people who say cats eat mainly introduced animals are
failing to take into account availability of prey. If there are 10
native birds and 100 introduced birds living in an area, of course
there will be a 10:1 ratio of introduced birds in the diet. The
animals don't discriminate. Perhaps any analysis of diet should
include surveys of prey items found to establish ratios of
availability. The ease with which the prey can be caught should be
factored in too, as I'd imagine it would be easier to catch a quail
than a possum (although I've heard of cats killing brushtailed possums
in Brisbane - very very scary).
Another argument that is used is that studies have only shown
extinctions on fragile islands. Any ecologist can tell you of the
problem of scale of experiments. The size of experiment you would
need to show that cats cause extinctions on mainland Australia is
beyond any government or university organisation, the funding is just
not there. The fact that cats have been shown to cause extinctions at
all is telling. At the same time it would be naieve to say that cats
were the sole cause. Foxes and habitat destruction caused by us can
also be major influences in small mammal and bird extinctions. That
doesn't mean we shouldn't deal with cats as a problem.
I'm not against fertility control, such as spay and release. In
combination with other methods of control it could have more chance of
success than other methods alone. Because of their territorial nature
and rapid breeding rates, cats will quickly repopulate areas where
they have been poisoned out, and for some time may even be at a higher
density of population than pre-poisoning because the territorial
boundaries are lost. I'm not saying that the spay and release method
will be any more successful, but it may be worth a shot.
Sorry to be so long winded. If people want some references on the
above I can provide a list of papers I read for a recent report on the
subject.
Regards,
Chris - Brisbane
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