Otago researcher Dr. Yolanda van Heezik has collected data on about 200
domestic cats around Dunedin: what prey they bring back; how far they
roam. The study started up last August and will run until this spring to
cover the four seasons. She reports as follows:
SO FAR ABOUT
1000 prey items have been reported by the cat-owners involved in the
study. Out of 208 cats in the study we have received records of prey
brought home by 99—so apparently nearly half the domestic cats do go off
hunting. Considering the prey items caught we get the following
– 42 different prey items caught.
– mice most frequently caught (237 items, 23%)
– rats only 8%
– blackbirds and sparrow most commonly caught birds (10%)
– exotic birds (12 species, 20%)
– native birds (waxeyes, fantail, tui, bellbird, 6%)
– lizard (common skink—11%)
– 19 types of invertebrate reported (26%)
– remaining—stoats, rabbits, a frog.
comprise 26% of the prey. Waxeyes are the most abundant native bird
caught and they are also the most abundant in the environment. Although
mice are a major item they are caught slightly less frequently than
birds. Rats are infrequent in the diet of these Dunedin cats.
the results from the point of view of the cats, rather than the prey, we
discover that only 22 of the 99 cats are catching rats, and 19 are
catching skinks. Insects are caught by 25 cats, and 75 cats have caught
at least one bird.
analysis (based on 6 days of tracking) gives a mean home range size of
2.6ha, and a range of 0.33—26.1ha. The longest distance one cat moved
from its house was about 400m. Half of our tracked cats lived next to
areas of native bush, and in all cases some locations were in the bush.
Problems with receiving the satellite signal under a canopy will have
resulted in an under-estimate of the number of locations in that
habitat. Males had slightly larger home ranges than females.
radio-tracking studies have shown most domestic cats don’t roam very
far: e.g. in Canberra, Australia home ranges were between 0.02—28ha.
Size depended on how many cats there were in the area, social dominance
of the cat, personality of the cat, locations of favoured hunting and
sunning sites and barriers, such as busy roads.
In New York
State average home range size was 0.24ha, with cats spending most of
their time in their own or their neighbours’ back gardens, despite
living next to a large nature reserve. Cats rarely entered the nature
reserve. The New York cats mainly brought back small mammals.
important to note that usually only a few individuals bring back most of
the prey. Cats seem to be opportunistic, catching the locally abundant
species. Rodents, especially mice, are most frequently caught. However,
a minority of cats seem to be specialists. A proportion of cats
occasionally bring back native birds. To assess the impact of this
predation on bird populations you would have to extrapolate up to
estimate how many cats lived in the urban area, and what proportion of
that total were catching native species. Then you’d have to have
estimates of the bird populations to assess whether the estimated number
of native birds caught was large enough to have a significant impact on
carried out counts of birds in various urban habitats, and the data
collection was designed so that I should be able to estimate the
densities of the more abundant species. I haven’t started to do that
As you must
be aware, the study has a number of biases. People with cats that
regularly catch prey may have been more likely to join the study. People
whose cats catch more are more likely to remain interested and keep
recording and sending in data, while some people might be less likely to
report the capture of a native species. We are assuming that what a cat
brings back is representative of what it catches!
collars do not seem to prevent cats from catching prey - although my
opinion is based on anecdotal evidence. Cats wearing the GPS collar,
which is quite bulky and weighs 125g, were able to catch prey.
Certainly, being fed doesn’t stop cats from catching prey.
David Speir I’d like to stress that the GBI Trust are not a crowd of
pet-haters! But we think we should know what our pets are doing. Of
course many domestic cats will catch some wild birds, and that probably
has only a minor impact on the birds. But it’s likely to be the good
hunters and the travellers that easily go feral, or have litters which
go feral. Then they can start to specialise on easy dinners—on brown
teal or Cook’s petrels for example. This is why neutering of domestic
cats will be a pre-requisite before the elimination of the feral cats.
We want to do that job once only!