But in spring and summer, Mrs Graham gives the birds a fighting chance by putting bell collars on her cats.
The Grahams' cats were part of a University of Otago study last year which found attaching bell collars to urban cats could save the lives of thousands of native birds annually.
A three-month study of 37 Dunedin cats known to be prolific hunters revealed the animals killed half the number of birds when the birds could hear them coming as they did when hunting silently.
Without collars, the cats caught 378 animals, including 82 birds, but only 41 birds were caught when the cats wore bells.
The most commonly caught native birds were fantails, bellbirds, grey warblers and silvereyes.
In the seven years the family had lived at Abbotsford, Mrs Graham said she had only ever seen her cats kill one native bird, a bellbird.
However, Mrs Graham said she agreed with the concept of cats wearing bell collars.
"I don't like the idea of them wearing collars all year round ...
"Mine get collars in the spring when the baby birds come along."
The study, by Dr Yolanda van Heezik, Dr Christoph Matthaei and student Jo Gordon from the department of zoology, asked the cats' owners to record the number of prey caught and brought back home during a six-week period while their pet was wearing a belled collar, and during another six-week period without a belled collar.
In New Zealand urban environments, there were on average 220 domestic cats per square kilometre, and each cat had an average travelling range of about 2.2ha, Dr Heezig said yesterday.
Previous studies showed domestic cats killed tens of thousands of native birds each year in this country.
Most cats might only kill one bellbird or fantail each a year, but the cumulative impact was likely to be huge, Dr Heezik said.
Owners could not be compelled to fit collars on their pets.
However, Dr Heezig said she would like them to think about doing so to protect bird biodiversity.
