House cat movements in Canberra suburbs adjacent to grassland and forest/woodland
areas were examined using radio-telemetry over 9 months. Information on the
composition of vertebrate prey caught by house cats in Canberra was also collected by
recording prey items deposited at cat owners' residences over 12 months.
Home range areas of 10 suburban house cats, and a colony of seven farm cats, were
examined using 95% convex polygons. Nocturnal home range areas of the suburban
cats varied between 0.02 and 27.93 ha (mean 7.89 ha), and were larger than diurnal
home range areas (range 0.02 to 17.19 ha - mean 2.73 ha). Nocturnal home range areas
of cats from the farm cat colony varied between 1.38 and 4.46 ha (mean 2.54 ha), and
were also larger than diurnal home range areas (range 0.77 to 3.70 ha - mean 1.70 ha).
Activity levels were greater at night than during the day, though diel activity patterns
varied seasonally in response to ambient temperature. Four suburban house cats moved
between 390 m and 900 m into habitat adjoining the suburb. Movements further than
100-200 m from the suburb edge were always made at night. Polygons describing the
home ranges of these animals were strongly spatially biased away from the suburban
environment, though the cats spent the majority of their time within the bounds of the
suburb.
In addition to nocturnal and diurnal effects, home range areas, and subsequently habitat
utilisation, appeared primarily determined by the density and spatial distribution of cats
utilising separate food resources, and the dominance of individual cats in local social
hierarchies, rather than gender or neutering effects. Home ranges of cats in the farm cat
colony overlapped extensively, as did those of cats living at the same suburban
residence. There was little or no overlap between the home ranges of cats from different
residences. Barriers, in the form of busy roads, appeared to also significantly influence
home range size and shape.
Within home range areas, house cat movements during the day appeared strongly
influenced by available cover (drains, tall grass, fences and shrubs etc.), and the location
of resting/sunning spots and hunting sites close to home. At night, movement patterns
appeared influenced by the location of favoured hunting sites toward the outer edges of
home range areas (in this study, tall grass and scrub/forest habitat, and farm buildings).
Nineteen hundred and sixty one prey items representing 67 species were reported or
collected. Sixty-four percent of the prey items were introduced mammals, with native
birds comprising 14%, introduced birds 10%, unidentified birds 3%, reptiles 7%,
amphibians 1% and native mammals 1%. Predation appeared to be largely
opportunistic with respect to spatial and temporal (daily and seasonal) prey availability
and accessibility. All amphibians and 62% of mammals taken by cats not confined at
night, were caught at night. In contrast, 70% of birds caught, and 90% of reptiles, were
taken during the day (45% of birds between 0600 h and 1200 h, and 61% of reptiles
between 1200 h and 1800 h). There was some evidence that small mammals are
preferred prey of house cats.
The mean number of prey items reported per cat over 12 months - 10.2 � 2.66 (2SE,
n=138) - was significantly lower than mean predation per cat per year - 23.3 � 6.16
(2SE, n=138) - estimated by cat owners before the prey survey began. Seventy percent
of cats were observed to catch less than 10 prey items over 12 months, but for 6% of
cats, more than 50 prey items were recorded. Because counts of the amount of prey
caught per house cat per unit time were highly positively skewed, data assumptions and
statistical parameters used to extrapolate results from the study sample of cats, to the
house cat population of Canberra, had a significant effect on estimates of total predation
in Canberra. The precision of the total predation estimate was low (± 25%), from a
sample of 0.3% of the Canberra house cat population. The accuracy of such estimates
are dependent on how representative the study cat sample is of the wider house cat
population, and on the proportion of prey items not observed by cat owners.
The total amount of prey taken was not significantly influenced by cat gender, age when
desexed, or cat breed. Nor did belling or the number of meals provided per day have a
significant influence on predatory efficiency. Cat age and the proportion of nights spent
outside explained approximately 11 % of the variation in the amount of prey caught by
individual cats. House cat density and distance to prey source areas (rural/grassland
habitat) explained 43% of variation in predation on introduced mammals and birds.
The impact of predation beyond suburb edges is likely to be most significant on
populations of small to medium sized arboreal and ground-dwelling mammals, because
of their nocturnal nature, and because they appear to be preferred prey types of house
cats. Impacts on diurnally active prey, such as most birds and reptiles, are likely to be
confined to within 200 m of residential housing (possibly further where good cover is
available). Properly enforced nocturnal confinement should restrict the range sizes of
cats that roam widely and utilisation of habitat beyond suburb edges, and also reduce
predation on mammals and amphibians. Night-time curfews however, are unlikely to
greatly reduce predation on diurnally active species, including most birds and reptiles.
Curfews are currently neither widely adopted nor effectively practiced in Canberra.
Estimates of predation by house cats, particularly extrapolated estimates, should be
treated with caution. They do not necessarily reflect relative impacts on different prey
types. Nor do high rates of predation prove prey populations are detrimentally effected,
particularly in urban environments. Nonetheless, on a small (backyard) scale in
suburban environments, and in habitat within 1 km of residential housing, including
isolated private properties, predation by individual cats may threaten populations of
native wildlife. Hunting by house cats is particularly undesirable in relatively
undisturbed habitat because of fundamental differences in the ecological processes
operating in these areas (especially isolated remnants) compared with contrived and
modified suburban environments. Adverse impacts on native fauna will always be
potentially greatest in undisturbed habitat adjacent to new residential developments
| Identifer | oai:union.ndltd.org:ADTP/218757 |
| Date | January 1995 |
| Creators | Barratt, David, n/a |
| Publisher | University of Canberra. Resource, Environmental & Heritage Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright David Barratt |
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