Cats again

To: "Reid" <>
Subject: Cats again
From: Peter Woodall <>
Date: Mon, 03 Sep 2001 16:57:34 +1000
At 16:01 3/09/2001 +1000, you wrote:
>Hello Chris and others
>I know that I am more than usually thick, but I really cannot define the
>theory of the 'de-sex and release' method.  To my way of thinking, the
>released cat continues to kill wildlife until it dies.  When it does die,
>its 'niche' in the environment would surely then be filled by a cat coming
>in from an adjacent area.  Maybe in a restricted area like Macquarie Island
>you could trap and de-sex all the cats before there was a significant
>percentage attrition due to death; that is, there would then be no
>replacements.  But I cannot see how it works in an 'open' environment, where
>replacements are available.
>Does anybody know of any authoritative study/article that supports this
>method, please?  And do they de-sex both male and female cats?
>Ralph Reid
Hi Ralph

I think that it has to do with this idea.

In most populations, mortality is related to the density of the population,
with high populations there is high mortality. This occurs mainly in the young.

That is why most trapping/shooting programs don't work, as soon as you reduce 
the population density, you also start to reduce mortality, and the remainder of
the population (especially the young) survive much better.

With the de-sex and release, you are reducing reproduction but still
maintaining a 
high mortality of the young, because the density is high.  As you get more
and more
desexed, especially of, say, the dominant males, then reproduction should
decline greatly
and the population should eventually die out..... 
but as you point out this only works on an isolated population with no

If only a few (fertile) pairs are left they will experience low density, low
(= high survival) and the population will rapidly build up again.



Dr Peter Woodall                          email = 
Division of Vet Pathology & Anatomy             
School of Veterinary Science.             Phone = +61 7 3365 2300
The University of Queensland              Fax   = +61 7 3365 1355
Brisbane, Qld, Australia 4072             WWW  =
"hamba phezulu" (= "go higher" in isiZulu)


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