(carnage estimates snipped)

Thanks, Stuart, for the more global perspective. For the more local side
of things, here's an anecdote from Discovery Park, Seattle.

For a long term study of Song Sparrow singing behavior, the lab I am
associated with here at the UW has been color banding song sparrows at
Discovery park for about 8 or 10 years (check next time you're there -
within our study area, 95% of the 150 or so males are banded). Recently,
we dropped an area from the study because it was the song sparrow black
hole (our site map actually says uses "Black Hole" to label that area, I
just noticed): birds banded there just disappeared, to be replaced by
unbanded birds that again disappeared once banded... The area is around
the ponds by the Indian Cultural Center. It is right on the edge of the
park, with a road running by it outside the park boundary, and on the road
are the houses of suburban Magnolia. And when walking throught this area
of the park it is common to see (you could see it coming, couldn't you?)
well fed tabbies sunning and hunting.

Although the Discovery Park situation is just a small part of the picture
(it annoys us researchers but doesn't threaten anything with extinction,
certainly) it relates to a few questions that have been discussed in the
thread so far, for instance (from Stuart MacKay):


> What species are being taken - if it's House Sparrows and Starlings, is
this OK ?

Well, in the Discovery Park case, the common bird species in the area are
native.


> What natural predators have been replaced by cats. OK cat numbers are
> probably huge in comparison but what was the predator pressure on birds
> before the arrival of humans ?

I can see two or three cats in ten minutes in an area of a few acres. I
would imagine that bobcats are about a thousand times rarer, and foxes and
coyotes at least a hundred times rarer. It's not even in the same
ballpark.


> Feral cats are in my opinion the biggest problem, particularly when it
> comes to island species, as Russell's example illustrates.

This is probably correct on a global scale - in island ecosystems
especially - but in Discovery Park, and I suspect in the U.S. and Britain
as a whole, house pets are the bigger problem due to sheer numbers. There
are feral cats in the park, but I have never seen one, and the only Black
Hole in our study area is the one that is commuting distance from the
feeding bowls. And the Stephen's Island Wren was actually wiped out by a
pet, not a feral cat.

Another point - a well fed cat makes a better mouser. If you put them out
in the barn to feed themselves, cats go hungry some of the time, lose
weight and energy, catch fewer mice, and often die. If you put them in
the barn with a good supply of food they stay sleek and healthy and mouse
because "it is their nature" instead of out of hunger. In their copious
leisure time, well fed cats catch mice much more effectively than hungry
ones. It is not true that cats only catch what they can eat, or that they
eat everything they catch. Motivation to hunt seems to be pretty
independent of hunger.

Emotionally, I like the idea of a cat hunting. I don't own one, though.
I'm not sure what I would do if I owned one.

blah blah blah

Chris Hill
cehill at u.washington.edu