On Fri, Jun 13, 2008 at 12:34:05PM +1000, Peter Shute wrote:
> As for the idea that suburban cats don't do that much damage, I hope
> it's true. But do the professor's comments take into account the
> possibility that if cats take all species at random, then pretty soon
> they'll have eliminated the rarer ones and only be seen to catch common
> ones? It may also be incorrect in areas that border more sensitive
> areas such as parks and bushland.
Individual cats certainly don't take prey at random. Studies have found
large behavioural variation between cats and that a fraction of suburban
cats account for the bulk of predation. But a study of Canberra domestic
cat prey found predation fairly evenly spread:
Species, abundance in canberra gardens(%), cat prey sample(%)
House sparrow 17.5 29.9 Preferred
Silvereye 15.4 17.8 Neutral
Starling 35.5 14.4 Avoided
Blackbird 5.0 9.8 Preferred
Crimson rosella 7.9 8.0 Neutral
Superb fairy-wren 2.3 4.0 Neutral
Magpie lark 5.5 3.7 Neutral
Eastern rosella 3.9 3.4 Neutral
Red wattlebird 4.5 3.2 Neutral
Yellow-faced honeyeater 2.1 3.2 Neutral
Golden whistler 0.5 2.6 Neutral
The author estimates over 100,000 birds taken annualy by canberra cats
so for example annually roughly 10,000 Crimson Rosella are killed by
cats in Canberra.
There may well species absent from the prey sample because cat predation
has previously reduced their density, a long term manipulative experiment
- excluding cats from part of Canberra for some years - would be more
interesting but also rather less feasible. I've appended another table
from the paper and a ref (doesn't seem to be freely available).
Andrew
species, number of prey caught, % of total, number of species
Mammals
House mouse 1095 55.84 1
Black rat 143 7.29 1
European rabbit 10 0.51 1
Other introduced species 3 0.15 2
Native species 14 0.71 5
Unknown 8 0.41 -
Subtotal 1273 64.92 10
Birds
Native species 273 13.92 41
Introduced species 196 10.00 6
Unknown 60 3.06 -
Subtotal 529 26.98 47
Reptiles 131 6.68 7
Amphibians 22 1.12 2
Fish 4 0.20 1
Unknown 2 0.10 -
Total 1961 67
Barratt, DG (1997a). Predation by house cats, Felis catus (L.), in
Canberra, Australia. I. Prey composition and preference. Wildlife
Research, 24, 263-77.
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