Individual hunting behaviour and prey specialisation in the house cat Felis catus: Implications for conservation and management

Abstract

Predators are often classed as prey specialists if they eat a narrow range of prey types, or as generalists if they hunt multiple prey types. Yet, individual predators often exhibit sex, size, age or personality-related differences in their diets that may alter the impacts of predation on different prey groups. In this study, we ask whether the house cat Felis catus shows individuality and specialisation in its hunting behaviour and discuss the implications of such specialisation for prey conservation and management. We first examine the prey types killed by cats using information obtained from cat owners, and then present data on cat hunting efficiency on different prey types from direct observations. Finally, we quantify dietary shifts in cats when densities of their preferred prey vary. Our results suggest that cats can exhibit individual, or between-phenotype, variation in hunting behaviour, and continue to hunt specific prey types even when these prey become scarce. From a conservation perspective, these findings have important implications, particularly if cats preferentially select rare or threatened species at times when populations of these species are low. Determining whether prey specialisation exists within a given cat population should therefore be useful for assessing the likely risk of localised prey extinctions. If risks are high, conservation managers may need to use targeted measures to control the impacts of specialist individual cats by using specific baits or lures to attract them. We conclude that individuality in hunting behaviour and prey preference may contribute to the predatory efficiency of the house cat, and suggest that studies of the ontogeny and maintenance of specialist behaviours be priorities for future research.

Full text

Applied
Animal
Behaviour
Science
173
(2015)
76–87
Contents
lists
available
at
ScienceDirect
Applied
Animal
Behaviour
Science
journa
l
h
om
epa
ge:
ww
w.elsevier.com/locate/applanim
Individual
hunting
behaviour
and
prey
specialisation
in
the
house
cat
Felis
catus:
Implications
for
conservation
and
management
Christopher
R.
Dickmana,∗,
Thomas
M.
Newsomea,b
aDesert
Ecology
Research
Group,
School
of
Biological
Sciences,
University
of
Sydney,
NSW
2006,
Australia
bDepartment
of
Forest
Ecosystems
and
Society,
Oregon
State
University,
Corvallis,
OR
97331,
USA
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Accepted
30
September
2014
Available
online
16
October
2014
Keywords:
Diet
Feral
cat
Predator
Predation
Prey
selectivity
Prey
switching
a
b
s
t
r
a
c
t
Predators
are
often
classed
as
prey
specialists
if
they
eat
a
narrow
range
of
prey
types,
or
as
generalists
if
they
hunt
multiple
prey
types.
Yet,
individual
predators
often
exhibit
sex,
size,
age
or
personality-related
differences
in
their
diets
that
may
alter
the
impacts
of
pre-
dation
on
different
prey
groups.
In
this
study,
we
asked
whether
the
house
cat
Felis
catus
shows
individuality
and
specialisation
in
its
hunting
behaviour
and
discuss
the
implica-
tions
of
such
specialisation
for
prey
conservation
and
management.
We
first
examined
the
prey
types
killed
by
cats
using
information
obtained
from
cat
owners,
and
then
presented
data
on
cat
hunting
efficiency
on
different
prey
types
from
direct
observations.
Finally,
we
quantified
dietary
shifts
in
cats
when
densities
of
their
preferred
prey
varied.
Twenty-
six
cats
that
returned
10
or
more
prey
items
to
their
owners
showed
marked
differences
in
prey
preferences
(P
<
0.001),
with
eight
cats
specialising
on
small
birds,
five
on
lizards,
four
on
black
rats
Rattus
rattus,
three
on
large
birds,
and
six
returning
multiple
prey
types.
Observations
of
182
hunting
attempts
by
15
cats
showed
significantly
high
hunting
effi-
ciency
(P
<
0.05)
by
four
cats
on
rodents
(83–100%
of
attacks
on
rodents
were
successful)
and
by
one
cat
on
rabbits
Oryctolagus
cuniculus
(94%
attack
success),
whereas
10
cats
hunted
two
or
three
prey
types
with
similar
efficiency.
At
two
field
sites
where
rabbits
were
pre-
ferred
cat-prey,
the
percentage
of
rabbit
in
the
diet
of
cats
showed
quadratic
relationships
against
rabbit
density,
with
cats
consuming
rabbits
when
they
were
undetected
in
surveys.
Our
results
suggest
that
cats
can
exhibit
individual,
or
between-phenotype,
variation
in
hunting
behaviour,
and
will
hunt
specific
prey
types
even
when
these
prey
become
scarce.
From
a
conservation
perspective,
these
findings
have
important
implications,
particularly
if
cats
preferentially
select
rare
or
threatened
species
at
times
when
populations
of
these
species
are
low.
Determining
whether
prey
specialisation
exists
within
a
given
cat
popu-
lation
should
therefore
be
useful
for
assessing
the
likely
risk
of
localised
prey
extinctions.
If
risks
are
high,
conservation
managers
may
need
to
use
targeted
measures
to
control
the
impacts
of
specialist
individual
cats
by
using
specific
baits
or
lures
to
attract
them.
We
conclude
that
individuality
in
hunting
behaviour
and
prey
preference
may
contribute
to
the
predatory
efficiency
of
the
house
cat,
and
suggest
that
studies
of
the
ontogeny
and
maintenance
of
specialist
behaviours
be
priorities
for
future
research.
©
2014
Elsevier
B.V.
All
rights
reserved.
∗Corresponding
author.
Tel.:
+61
2
9351
2318;
fax:
+61
2
9351
4119.
E-mail
address:
chris.dickman@sydney.edu.au
(C.R.
Dickman).
1.
Introduction
Predatory
animals
are
commonly
placed
into
one
of
two
categories
depending
on
the
variety
of
prey
that
http://dx.doi.org/10.1016/j.applanim.2014.09.021
0168-1591/©
2014
Elsevier
B.V.
All
rights
reserved.

C.R.
Dickman,
T.M.
Newsome
/
Applied
Animal
Behaviour
Science
173
(2015)
76–87
77
they
include
in
their
diet.
Specialist
predators,
on
the
one
hand,
consume
a
narrow
range
of
prey
and
may
be
criti-
cally
dependent
on
just
one
or
two
prey
species
(Erlinge
et
al.,
1984).
Such
predators
often
have
morphological
or
physiological
adaptations
that
increase
their
hunting
effi-
ciency
and
ability
to
handle
or
process
particular
prey,
but
decrease
their
efficiency
in
tackling
alternative
prey.
Exam-
ples
include
ant-mimicking
spiders
that
so
resemble
their
formicid
prey
in
appearance,
odour
and
behaviour
that
they
can
raid
ant
colonies
with
little
risk
(Castanho
and
Oliveira,
2009),
frog-eating
bats
that
use
the
specific
calls
of
anurans
to
target
their
prey
(Ryan,
2011),
and
myrme-
cophagous
animals
that
use
specialised
structures
(e.g.
spade-like
digging
claws,
long,
sticky
tongues)
to
expose
and
then
consume
subterranean
termites
or
ants
(Redford,
1987).
On
the
other
hand,
generalist
predators
have
rela-
tively
broad
diets
(Erlinge
et
al.,
1984).
Some
generalists
eat
different
prey
types
in
rough
proportion
to
their
availabil-
ity
in
the
environment,
consuming
them
either
via
bulk
ingestion
(e.g.
baleen
whales
that
consume
krill,
fish
and
other
small
marine
organisms;
Watkins
and
Schevill,
1979)
or
with
the
use
of
traps
that
indiscriminately
catch
diverse
prey
(e.g.
orb-weaving
spiders;
Nentwig,
1985).
Other
gen-
eralists
have
broad
diets,
but
prefer
or
select
some
types
of
prey
more
than
others
(Corbett
and
Newsome,
1987).
The
specialist–generalist
dichotomy
is
usually
applied
to
populations
or
species
of
predators
to
describe
how
the
animals
behave
collectively.
In
the
case
of
specialists,
all
individuals
in
a
population
will
show
similar
foraging
behaviour
and
share
a
common,
restricted
diet.
In
the
case
of
generalists,
however,
the
broad
dietary
breadth
exhib-
ited
by
a
population
may
arise
in
two
ways.
Firstly,
all
members
of
the
same
population
may
have
broad,
gen-
eralised
diets
that
include
all
components
of
the
prey
spectrum
and
thus
differ
little
from
individual
to
individ-
ual.
Secondly,
population
members
may
each
specialise
on
different
components
of
the
available
prey
spectrum.
Here,
individual
animals
behave
as
foraging
specialists
but
the
population,
when
viewed
collectively,
has
a
generalist
diet.
These
two
aspects
of
diet
niche
breath
were
dis-
tinguished
by
Van
Valen
(1965)
and
Roughgarden
(1972,
1974a)
and
labelled,
respectively,
within-phenotype
and
between-phenotype
components.
Early
research
tended
to
emphasise
the
theoretical
importance
of
these
diet
niche
components,
but
empirical
studies
showed
further
that
they
could
be
employed
to
interpret
patterns
of
foraging
behaviour,
competition
and
species
composition
in
real
world
communities
of
fish,
lizards,
birds
and
other
preda-
tors
(Orians,
1971;
Roughgarden,
1974a,b).
Subsequent
work
has
shown
that
predators
often
exhibit
sex,
size,
age
or
personality-related
differences
in
their
diets
(Brickner
et
al.,
2014;
Dickman,
1988),
and
that
these
differences
can
spread
the
impacts
of
predation
across
diverse
communi-
ties
of
prey
species
(Bolnick
et
al.,
2003;
Yip
et
al.,
2014).
Recent
studies
have
uncovered
between-phenotype
foraging
specialisations
in
populations
of
sea
otters
(Estes
et
al.,
2003),
guillemots
(Woo
et
al.,
2008),
and
sharks
(Matich
et
al.,
2011)
and,
increasingly,
in
large
felids.
For
example,
Ross
et
al.
(1997)
and
Knopff
and
Boyce
(2007)
provided
evidence
of
differential
specialisation
on
deer
Odocoileus
spp.
and
bighorn
sheep
Ovis
canadensis
by
individual
cougars
Puma
concolor
in
Canada;
Elbroch
and
Wittmer
(2013)
documented
further
individual-level
hunting
specialisations
by
the
same
species
in
Patago-
nia.
Similar
individual-level
specialisation
on
different
prey
species
has
been
shown
within
populations
of
jaguar
Pan-
thera
onca
(Cavalcanti
and
Gese,
2010),
Amur
tiger
Panthera
tigris
altaica
(Miller
et
al.,
2013)
and
perhaps
Eurasian
lynx
Lynx
lynx
(Odden
et
al.,
2006).
Individuality
in
predator
hunting
behaviour
may
arise
as
a
learning
process
when
young
animals
are
being
taught
about
sources
of
food
by
parents
(Kuo,
1930;
Woo
et
al.,
2008),
when
independent
animals
discover
new
sources
of
prey
or
hunting
locations
(Cook
et
al.,
2006),
or
if
declines
in
prey
numbers
force
animals
to
exploit
different
components
in
the
remaining
prey
base
(Svanbäck
and
Bolnick,
2005,
2007).
Individual-
level
dietary
specialisation
by
predators
on
particular
prey
can
have
dramatic
effects
on
food
web
dynamics
(Tinker
et
al.,
2008)
and,
if
preferred
prey
species
are
already
scarce
or
threatened,
targeted
predation
may
place
them
at
heightened
risk
of
local
extinction
(Pettorelli
et
al.,
2011).
Felid
predators
pose
particular
problems
for
livestock
if
they
learn
to
specialise
on
them
(e.g.
Linnell
et
al.,
1999);
in
settled
areas,
rogue
felids
sometimes
hunt
and
kill
com-
panion
animals
and
may
even
target
people
themselves
(Frump,
2006).
In
this
study,
we
asked
whether
the
house
cat
Felis
catus
shows
similar
individuality
in
its
hunting
behaviour
to
some
of
its
larger
relatives,
and
marshalled
evidence
from
several
disparate
studies
to
address
this
question.
We
focussed
on
the
house
cat
for
several
reasons.
Firstly,
F.
catus
is
ubiquitous.
It
is
kept
as
a
house
pet
or
used
as
a
pest
control
agent
on
every
continent
except
Antarctica,
and
has
established
un-owned,
stray
or
feral,
populations
world-
wide
(Denny
and
Dickman,
2010).
Secondly,
both
domestic
and
un-owned
cats
have
been
shown
to
exact
an
enor-
mous
toll
on
wildlife.
In
the
United
States
(US),
for
example,
Dauphiné
and
Cooper
(2009)
concluded
that
cats
kill
over
a
billion
birds
annually.
Loss
et
al.
(2013)
estimated
further
that
cats
kill
1.4–3.7
billion
birds
and
6.9–20.7
billion
mam-
mals
each
year
in
the
US,
with
69%
of
bird
deaths
and
89%
of
mammal
deaths
caused
by
un-owned
cats
and
the
remain-
der
by
their
domestic
counterparts.
In
Canada,
Blancher
(2013)
put
the
annual
loss
of
birds
to
cats
at
100–350
mil-
lion,
with
most
falling
victim
to
feral
cats.
Thirdly,
there
is
some
evidence
that
cats
may
develop
marked
individual-
ity
in
hunting
and
killing
behaviour,
targeting
such
unusual
prey
as
small
bats
(Ancillotto
et
al.,
2013)
and
potentially
putting
rare
species
at
particular
risk.
For
example,
no
more
than
four
cats
were
implicated
by
Gibson
et
al.
(1994)
in
the
demise
of
the
rufous
hare-wallaby
Lagorchestes
hirsu-
tus
at
reintroduction
sites
in
the
Tanami
Desert
of
central
Australia,
and
a
similar
number
of
cats
is
thought
to
have
extirpated
the
endemic
wren
Traversia
lyalli
on
Stephens
Island,
New
Zealand,
within
5
years
of
their
introduction
(Atkinson
and
Bell,
1973;
Galbreath
and
Brown,
2004).
The
predatory
impacts
of
cats
are
notoriously
difficult
to
manage
(Denny
and
Dickman,
2010;
Dickman,
2014;
Loyd
and
DeVore,
2010).
By
understanding
how
cats
hunt,
and
the
extent
to
which
they
show
individuality
in
hunting
behaviour,
we
can
gain
clearer
insight
into
both
manage-
ment
tactics
and
strategy.

78
C.R.
Dickman,
T.M.
Newsome
/
Applied
Animal
Behaviour
Science
173
(2015)
76–87
Fig.
1.
Map
of
eastern
Sydney,
Australia,
showing
the
four
bushland
reserves
(study
sites)
and
surrounding
areas
used
to
test
the
hypothesis
that
individual
cats
will
show
distinct
preferences
for
particular
prey
types.
Inset:
map
of
Australia
showing
other
locations
used
in
this
study
(Note:
North
Head
and
Ryans
Reserve,
near
Kellerberrin,
are
not
shown,
but
are
close
to
Sydney
and
Rottnest
Island,
respectively.).
Based
on
the
studies
cited
above,
it
is
reasonable
to
expect
that
populations
of
house
cats
may
show
between-
phenotype
variation
in
hunting
behaviour
and
preferences
for
particular
prey
types,
and
will
do
so
irrespective
of
prey
abundance.
Given
these
expectations,
we
derived
and
tested
three
contingent
hypotheses.
Thus,
within
cat
pop-
ulations
we
predicted
that:
(1)
Individual
cats
will
show
distinct
preferences
for
par-
ticular
prey
types,
(2)
Individual
cats
will
vary
in
the
efficiency
with
which
they
hunt
different
prey
types,
and
(3)
Preferred
prey
will
be
targeted
by
cats
irrespective
of
prey
density.
We
use
our
results
to
provide
suggestions
for
managers
who
are
charged
with
controlling
cat-impacts.
2.
Materials
and
methods
To
test
the
three
hypotheses,
we
present
observations
of
both
domestic
and
un-owned
cats
using
different
tech-
niques
in
a
wide
variety
of
locations.
The
methods
used
to
test
each
hypothesis
are
described
separately
below.
We
confirm
that
all
procedures
comply
with
the
ethical
guidelines
of
the
International
Society
for
Applied
Ethology
(Sherwin
et
al.,
2003).
2.1.
Hypothesis
1:
do
individual
cats
show
distinct
preferences
for
particular
prey
types?
To
assess
whether
cats
show
preferences
for
particu-
lar
types
of
prey,
we
studied
a
sample
of
domestic
cats
in
suburban
Sydney,
Australia,
using
information
obtained
from
the
cats’
owners.
Following
the
pioneering
studies
of
Paton
(1990,
1991),
potential
participants
were
contacted
initially
by
letter-drops
to
residential
post
boxes,
and
peo-
ple
in
residences
with
one
or
more
cats
were
invited
to
take
part
in
a
further
questionnaire
survey.
The
areas
targeted
for
the
survey
were
in
the
city’s
eastern
suburbs
within
a
0.5
km
radius
of
four
adjacent
bushland
reserves
rang-
ing
in
size
from
1.2–18
ha
(Fig.
1).
These
reserves
–
Cooper
Park,
Harbour
View
Park,
Trumper
Park
and
the
Thomas
Hogan
Reserve
–
were
selected
because
preliminary
obser-
vations
indicated
that
they
contained
diverse
populations
of
potential
prey
for
cats
(e.g.
reptiles,
birds,
introduced
rodents,
native
marsupials),
and
also
that
cats
frequently
hunted
there
(Dickman,
2009).
Residents
who
agreed
to
participate
were
asked
a
series
of
questions
about
the
age,
sex,
breed,
reproductive
status
(sterilised
or
intact)
and
number
of
cats
in
their
care,
whether
the
cats
had
regular
and
reliable
access
to
food,
whether
the
cats
were
free
to
roam
by
day
or
night,
and
whether
cats
returned
captured
prey
animals
to
the
owners’
homes.
Residents
were
also
asked
if
they
would
be
prepared
to
collect
or
record
the
prey
animals
that
their
pets
killed
and
returned
over
the
course
of
a
year.
Surveys
were
carried
out
in
1993–1994
and
1997–1998
and
we
pooled
the
results
of
both
surveys
for
analysis.
We
present
a
subset
of
the
overall
results
here,
and
summarise
only
the
data
on
prey
that
were
returned
by
cats
that
had
no
restrictions
placed
on
their
movements
or
temporal
activity
by
their
owners.
To
determine
whether
predators
prefer
particular
prey,
the
types
of
prey
killed
should
ideally
be
compared
with
the
availability
of
those
types
in
the
environment
(Knopff
and
Boyce,
2007).
However,
when
prey
types
vary
markedly
in
their
activity,
habitat
use
and
behaviour,
as
may
be
expected
of
prey
in
the
different
classes
of
vertebrates,
their
relative
availability
to
predators
is
difficult
to
measure
and
comparisons
between
groups
become
unreliable
(Spencer
et
al.,
2014).
In
this
study,
we
made
no
attempt
to
docu-
ment
the
availability
of
the
different
prey
groups.
However,

C.R.
Dickman,
T.M.
Newsome
/
Applied
Animal
Behaviour
Science
173
(2015)
76–87
79
as
our
study
cats
had
access
to
essentially
the
same
suite
of
prey
in
the
four
co-located
reserves,
we
assumed
that
any
differences
detected
in
the
prey
they
killed
arose
due
to
differences
in
preference
rather
than
availability.
A
further
assumption
we
made
was
that
cats
would
return
a
repre-
sentative
sample
of
prey
to
their
owners.
Domestic
cats
can
be
expected
to
consume
some
prey
and
to
leave
other
prey
in
situ
after
subduing
it,
and
hence
may
return
only
a
frac-
tion
of
the
prey
that
they
kill
(e.g.
Baker
et
al.,
2005;
Lepczyk
et
al.,
2003;
Tschanz
et
al.,
2011).
However,
we
were
less
interested
in
the
numbers
of
prey
than
in
the
types
of
prey
that
cats
kill,
and
note
that
the
distribution
of
prey
types
returned
to
owners
was
similar
to
that
in
the
diet
of
cats
in
the
survey
area
(Dickman,
2009).
2.2.
Hypothesis
2:
do
individual
cats
vary
in
the
efficiency
with
which
they
hunt
different
prey
types?
We
tested
this
hypothesis
by
making
direct
observa-
tions
of
hunting
cats
at
five
different
locations
in
England
and
Australia.
The
first
location,
at
Shotover
Country
Park,
near
Oxford,
UK,
comprises
a
mosaic
of
wooded
and
cleared
areas
on
rolling
hills
that
provide
high
vantage
points.
This
site
contains
a
diverse
array
of
mammals
and
birds
as
well
as
several
species
of
reptiles
(Dickman,
1987;
Whitehead
et
al.,
2010),
and
was
visited
either
once
or
twice
a
week
for
5–6
h
on
each
occasion
between
April
and
July,
1983.
In
Australia,
observations
of
cats
were
made
in
the
Simpson
Desert,
Queensland,
at
North
Head,
New
South
Wales,
and
near
Kellerberrin
and
on
Rottnest
Island,
Western
Australia
(Fig.
1)
for
intensive
periods
of
5–8
days
at
different
times
between
March
1986
and
May
2008,
with
observations
lasting
3–5
h
on
each
occasion.
Observations
in
the
Simp-
son
Desert
were
made
near
Ethabuka
homestead
in
open
sand
dune
habitat
dominated
by
spinifex
Triodia
basedowii
grassland
(Dickman
et
al.,
2014).
The
North
Head
site
com-
prises
dense
coastal
heath,
forest
and
open
cleared
areas
(Scott
et
al.,
1999),
as
does
the
site
on
Rottnest
Island,
although
most
observations
at
the
latter
site
were
made
in
open
reforestation
plots
near
the
Rottnest
Island
Bio-
logical
Research
Station
(Dickman,
1992).
At
Kellerberrin,
observations
of
cats
were
made
in
remnant
woodland
in
Ryans
Reserve
(Smith
et
al.,
1997).
All
the
Australian
sites
contain
small
or
medium-sized
(<5
kg)
native
mammals,
introduced
mammals
such
as
rabbits
Oryctolagus
cunicu-
lus,
black
rats
Rattus
rattus
or
house
mice
Mus
musculus,
and
diverse
assemblages
of
birds
and
reptiles.
In
all
the
study
locations,
cats
were
probably
un-owned.
We
confirmed
in
discussions
with
the
managers
of
the
only
properties
within
a
radius
of
∼9
km
of
Ryans
Reserve
and
>50
km
of
Ethabuka
homestead
that
they
did
not
own
pet
cats,
and
cat-ownership
was
prohibited
at
the
other
sites
owing
to
their
status
as
sites
protected
for
conservation.
In
consequence
of
this,
cats
at
each
location
likely
obtained
most
or
all
of
their
food
from
hunting.
However,
because
of
their
proximity
to
human
settlement,
the
cats
in
each
location
were
accustomed
to
human
presence
and
could
be
observed
at
distances
of
≥10
m
without
any
evident
effect
on
their
behaviour
or
activity.
By
selecting
elevated
van-
tage
points
on
the
sides
of
hills
above
where
cats
were
detected,
it
was
then
possible
to
observe
hunting
behaviour
and
score
both
successful
and
unsuccessful
kill-attempts.
These
locations
also
allowed
us
to
shift,
as
needed,
from
point
to
point
on
the
hillsides
to
keep
individual
cats
in
view
as
they
moved.
We
used
binoculars
to
aid
observa-
tions
so
that
hunting
attempts
by
cats
could
be
detected
and
scored
even
in
habitats
with
heavy
ground
cover.
At
four
locations
we
made
most
observations
(>95%)
by
day
or
just
after
dusk
as
initial
searches
at
night
failed
to
find
any
cats
that
were
active.
At
North
Head,
however,
pilot
searches
indicated
that
some
cats
were
active
in
the
first
half
of
the
night,
and
here
nearly
half
of
all
observations
(14/29)
were
made
after
dusk
but
before
midnight
under
dim
white
light
or
red
light.
Photographs
were
taken
of
all
cats
that
were
observed,
and
this
allowed
us
to
tally
the
number
of
strikes
they
made
on
potential
prey
on
an
individual
basis.
We
express
the
hunting
efficiency
of
indi-
vidual
cats
for
different
prey
types
simply
as
the
percentage
of
capture
attempts
that
resulted
in
a
successful
kill.
2.3.
Hypothesis
3:
are
preferred
prey
targeted
by
cats
irrespective
of
prey
density?
Two
of
the
above
study
locations,
Ryans
Reserve
and
Ethabuka,
were
used
to
test
our
third
hypothesis.
Ini-
tial
observations
of
cats
in
these
locations
and
analyses
of
their
diet
from
collected
scats
(see
below)
indicated
that
rabbits
were
preferred
prey
for
most
individuals,
and
smaller
mammals,
birds
and
lizards
collectively
formed
a
minor
part
of
the
diet
(<20%
by
scat
volume
at
Ryans
Reserve;
∼35%
by
volume
at
Ethabuka).
At
Ryans
Reserve,
rabbits
occurred
in
the
reserve
itself
but
were
present
in
much
greater
numbers
in
land
surrounding
the
reserve
that
was
used
for
wheat
cropping
and
sheep
grazing.
To
keep
their
numbers
at
levels
where
crop
damage
was
tol-
erable,
local
landholders
baited
rabbits
irregularly
with
oats
laced
with
the
toxin
sodium
fluoroacetate,
or
1080.
Baits
were
set
twice
during
our
2½
year
study
at
Ryans
Reserve,
reducing
rabbit
numbers
dramatically
on
each
occasion.
At
Ethabuka,
rabbits
were
localised
near
the
homestead
and
two
further
specific
sites
around
natural
water
springs
to
the
north
and
south
of
the
homestead.
No
baits
or
other
control
measures
were
established
at
these
locations,
but
rabbit
numbers
in
this
arid
environ-
ment
fluctuated
depending
on
the
amount
of
rain
that
fell
during
the
summer
rainy
season.
During
our
4-year
study
at
this
location,
from
mid-1990
to
mid-1994,
summer
rainfall
(November–February)
varied
from
98
mm
in
1992–1993
to
439
mm
in
1990–1991
(Dickman
et
al.,
2010),
with
rab-
bit
numbers
generally
rising
within
4–6
months
of
heavy
rainfall
events
and
falling
again
within
a
year
as
conditions
dried
out.
We
used
spotlight
counts
along
standardised
transects
to
obtain
an
index
of
rabbit
numbers
at
each
location,
using
either
a
single
100
W
spotlight
(Ryans
Reserve)
or
two
spot-
lights
(Ethabuka)
from
a
vehicle
moving
at
10–15
km/h.
Transects
were
traversed
after
dusk
when
rabbits
were
active,
at
random
times
between
20:30
h
and
01:00
h,
and
were
restricted
to
calm,
dry
conditions
when
good
visibil-
ity
was
assured.
Although
spotlight
counts
can
be
biased
if
carried
out
between
different
habitats
and
under
differ-
ent
environmental
conditions
(Newsome
et
al.,
2014;
Vine

80
C.R.
Dickman,
T.M.
Newsome
/
Applied
Animal
Behaviour
Science
173
(2015)
76–87
et
al.,
2009),
we
assume
that
detectability
of
rabbits
was
relatively
constant
here
owing
to
the
open
nature
of
the
habitat
in
each
study
location
and
our
attempts
to
ensure
comparability
in
the
conditions
under
which
observations
were
made.
The
transect
at
Ryans
Reserve
was
∼10
km
long
and
that
at
Ethabuka
∼12
km;
two
replicate
counts
were
made
along
each
transect
on
three
to
six
visits
to
each
loca-
tion
for
each
year
of
the
respective
studies.
Counts
were
averaged
each
sampling
session
and
standardised
to
yield
an
estimate
of
rabbits
seen
per
km.
Cat
scats
were
collected
on
each
sampling
occasion
along
the
spotlighting
transects,
from
walking
tracks
at
each
location
and
from
rabbit
warrens;
the
same
sites
were
searched
on
each
occasion
to
increase
confidence
that
scats
had
been
produced
in
the
interval
since
the
previous
sam-
pling
occasion.
Scats
from
the
first
sampling
session
at
each
location
were
discarded
as
their
age
was
unknown.
Col-
lected
scats
were
placed
in
individually
labelled
bags,
dried
and
later
pulled
apart
in
the
laboratory
to
identify
prey
that
had
been
consumed.
Mammals
were
identified
from
teeth,
claws
or
hair,
birds
from
feathers,
beaks
or
claws,
reptiles
from
scales
and
often
from
hard
remains
such
as
feet,
and
invertebrates
from
mouthparts,
antennae,
legs
and
other
hard
parts
of
the
exoskeleton;
plant
remains
were
noted
but
not
identified
further.
Only
mammals
were
identified
to
species,
with
identification
relying
principally
on
the
external
characteristics
and
cross-sectional
appearance
of
hair
(Brunner
and
Triggs,
2002).
We
estimated
the
volu-
metric
contribution
of
different
prey
types
in
each
scat
by
eye,
but
for
simplicity
present
dietary
results
as
the
per-
centage
frequency
of
occurrence
(the
number
of
samples
containing
a
specific
prey
type
divided
by
the
total
number
of
samples
×
100).
2.4.
Data
management
and
statistical
analyses
Preliminary
inspection
of
the
questionnaire
survey
results
(hypothesis
1)
showed
that
only
some
cats
returned
prey
to
their
owners,
and
also
that
many
cats
returned
too
few
prey
to
determine
any
dietary
pattern.
Hence,
analyses
were
restricted
to
those
cats
that
presented
≥10
individual
prey
items
to
their
owners
over
the
duration
of
the
study.
To
identify
similarities
and
differences
in
the
prey
that
cats
returned,
we
first
grouped
prey
into
nine
categories:
rat,
common
ringtail
possum
Pseudocheirus
peregrinus,
com-
mon
brushtail
possum
Trichosurus
vulpecula,
large
bird,
small
bird,
lizard,
reptile
(other),
frog,
and
invertebrate.
From
the
records
provided
by
respondents
it
was
not
pos-
sible
to
reliably
split
the
non-mammalian
groups
into
finer
categories.
However,
the
large
bird
category
comprised
largely
corvids
and
the
crested
pigeon
Ocyphaps
lophotes,
all
of
which
were
distinguished
by
respondents.
For
analy-
sis,
we
constructed
a
matrix
of
Bray–Curtis
dissimilarities
of
the
prey
captured
by
cats,
after
first
standardising
the
prey
data
to
1.0
for
each
cat
by
dividing
the
number
of
each
type
of
prey
returned
by
the
total
number.
Standardising
reduced
any
confounding
effects
of
differing
sample
size
between
cats
(Quinn
and
Keough,
2002).
The
matrix
was
then
subjected
to
ordination
by
non-metric
multidimen-
sional
scaling
(nMDS).
We
used
two
dimensions
to
improve
interpretability
of
the
ordination,
and
used
the
lowest
stress
value
from
20
random
starts
(Quinn
and
Keough,
2002).
To
further
assess
the
association
between
individ-
ual
cats
and
the
prey
that
they
captured,
a
chi-squared
contingency
test
was
computed
using
the
raw
frequency
data.
Finally,
for
descriptive
purposes
we
calculated
a
sim-
ple
measure
of
the
diversity
of
prey
types
returned
by
cats
based
on
Simpson’s
diversity
index,
D:
D
=ni(ni−
1)
N{N
−
1}
where
ni=
the
number
of
individuals
in
the
ith
prey
type,
and
N
=
the
total
number
of
individuals.
Expressed
as
the
complement
(1
−
D),
Simpson’s
index
is
0
if
only
one
prey
type
is
present
and
approaches
1
if
there
are
many.
While
simple,
this
index
is
intuitive
and
robust
(Magurran,
2004).
The
hunting
efficiencies
of
individual
cats
(hypoth-
esis
2)
were
quantified
by
comparing
the
numbers
of
prey
in
each
category
that
were
observed
to
be
success-
fully
versus
unsuccessfully
attacked
and,
for
cats
with
≥10
observations,
differences
between
prey
types
detected
using
chi-squared
contingency
analyses.
Tests
of
hypoth-
esis
3
were
made
by
plotting
the
percentage
frequency
of
occurrence
of
rabbit
in
cat
scats
against
estimates
of
rabbit
abundance
at
different
sampling
times
in
the
two
study
locations;
curves
of
best
fit
were
evaluated
simply
by
improvement
in
R2(Quinn
and
Keough,
2002).
Non-metric
multidimensional
scaling
was
implemented
in
PRIMER
v.
5
(Clarke
and
Warwick,
1994)
and
other
analyses
in
SPSS
v.
15.0
(SPSS,
2006).
3.
Results
3.1.
Hypothesis
1:
do
individual
cats
show
distinct
preferences
for
particular
prey
types?
Overall,
362
people
responded
from
a
total
of
779
letter-
drops,
giving
a
response
rate
of
46%.
Of
the
respondents,
159
people
(44%)
owned
cats
that
had
potential
access
to
the
bushland
reserves
and
agreed
to
keep
a
log
of
the
prey
that
their
pet
returned;
of
these,
105
people
actually
did
so.
At
least
51
cats
were
reported
as
returning
no
prey
to
their
owners,
with
the
dataset
presented
below
comprising
62
cats
(six
people
returned
information
on
two
or
three
cats
under
their
care).
These
animals
comprised
34
females
and
28
males,
all
neutered,
and
aged
from
1
to
12
years
at
the
beginning
of
the
study.
Records
of
the
prey
returned
by
these
cats
were
collected
over
periods
of
7–13
months.
In
total,
the
cats
returned
667
prey
items
to
their
own-
ers,
with
a
range
of
1–58
per
individual.
Small
birds
were
returned
most
often,
by
41
cats
(n
=
245, ¯
x=
3.95
±
6.65
SD,
range
0–29
per
cat).
The
superb
fairy-wren
Malurus
cya-
neus,
eastern
yellow
robin
Eopsaltria
australis,
welcome
swallow
Hirundo
neoxena,
and
rainbow
lorikeet
Trichoglos-
sus
haematodus
were
among
the
most
commonly
reported
native
birds,
as
was
the
Indian
myna
Acridotheres
tristis
among
the
introduced
species.
Lizards
were
returned
by
33
cats
(n
=
162, ¯
x
=
2.61
±
5.57
SD,
range
0–28
per
cat)
and
comprised
the
skinks
Lampropholis
delicata,
L.
guichenoti,
Saproscincus
mustelinus
and
Eulamprus
quoyii.
Rats
were
returned
by
28
cats
(n
=
131, ¯
x
=
2.11
±
5.24
SD,
range
0–34
per
cat);
all
were
probably
black
rats,
as
no
other
Rattus

C.R.
Dickman,
T.M.
Newsome
/
Applied
Animal
Behaviour
Science
173
(2015)
76–87
81
Fig.
2.
Two
dimensional
ordination
(stress
=
0.14)
of
major
types
of
prey
returned
by
domestic
house
cats
Felis
catus
to
their
owners
living
around
bushland
reserves
in
Sydney,
Australia.
Data
are
based
on
26
cats
that
returned
≥10
prey
items
over
the
course
of
study.
species
are
known
to
occur
in
the
survey
area.
Large
birds
were
returned
by
10
cats
(n
=
40, ¯
x
=
0.65
±
2.14
SD,
range
0–11
per
cat)
and
invertebrates
(including
blattids,
phas-
mids
and
large
scolopendrid
centipedes)
by
23
cats
(n
=
55,
¯
x
=
0.89
±
1.56
SD,
range
0–7
per
cat).
Frogs
and
the
two
species
of
possum
were
returned
infrequently,
by
five
to
eight
cats
in
each
case;
one
cat
returned
three
ring-
tail
possums
and
another
cat
returned
six
frogs
(probably
Limnodynastes
peronii).
Three
reptiles
in
the
‘other’
cate-
gory
were
returned.
All
were
snakes;
one
was
a
golden
crowned
snake
Cacophis
squamulosus,
another
a
juvenile
green
tree
snake
Dendrelaphis
punctulatus,
and
the
third
was
not
identified.
Twenty-six
cats
returned
10
or
more
prey
items
to
their
owners,
with
very
marked
differences
in
the
prey
types
that
were
represented
(2100 =
987.95,
P
<
0.001;
data
on
the
two
species
of
possum,
‘other’
reptiles
and
frogs
were
omitted
from
analysis
due
to
insufficient
numbers).
Ordi-
nation
identified
five
groups
within
this
subset
of
cats,
four
that
exhibited
some
degree
of
specialisation
on
particu-
lar
types
of
prey
and
one
where
no
clear
specialisation
could
be
identified
(Fig.
2).
The
largest
group
(n
=
8)
com-
prised
cats
that
captured
small
birds.
Small
birds
comprised
66.7–100%
of
the
prey
returned
by
these
cats,
and
resulted
in
a
prey-take
diversity
(1
−
D)
of
0.23
±
0.18
SD.
Five
cats
focused
on
lizards
(87.5–94.4%
of
the
prey
items
returned,
1
−
D
=
0.16
±
0.05
SD),
four
on
rats
(81.8–97.1%
of
prey
items
returned,
1
−
D
=
0.18
±
0.11
SD)
and
three
on
large
birds
(70–90%
of
prey
items
returned,
1
−
D
=
0.30
±
0.14).
Six
cats
showed
no
evident
specialisation
on
any
prey
type,
returning
four
to
six
types
of
prey
to
their
owners
and
with
no
prey
type
representing
more
than
55%
of
their
catch.
The
diversity
value
for
these
cats
(1
−
D
=
0.68
±
0.04
SD)
was
greater
than
that
for
all
other
groups
identified
in
Fig.
2
(one-factor
ANOVA,
F4,21 =
17.22,
P
<
0.001),
but
there
was
no
difference
among
the
four
groups
that
predominantly
captured
and
returned
one
type
of
prey
(Tukey
post
hoc
tests,
P
=
0.43–0.99
for
all
between-pair
comparisons).
3.2.
Hypothesis
2:
do
individual
cats
vary
in
the
efficiency
with
which
they
hunt
different
prey
types?
In
total,
we
recorded
182
hunting
attempts
by
15
cats
across
the
five
study
locations
in
>400
h
of
field
observa-
tion
(Table
1).
Most
observations
were
made
while
waiting
for
animals
to
appear,
but
about
20%
of
observations
were
made
opportunistically.
Nine
cats
were
observed
to
make
≥10
attacks
on
prey
and,
of
these,
four
exhibited
greatest
efficiency
(83–100%
of
attacks
successful)
when
hunting
rodents,
and
one
was
most
efficient
(94%)
when
hunting
rabbits
(Table
1).
These
individuals
achieved
maximal
suc-
cess
of
50%
when
hunting
any
other
types
of
prey.
The
remaining
cats
hunted
two
or
three
types
of
prey
with
similar
efficiency
(Table
1).
It
was
not
always
clear
if
a
prey
item
was
killed
in
a
successful
attack;
rodents,
in
particular,
were
often
sub-
dued
and
‘swatted’
repeatedly
by
a
cat’s
forepaws
while
still
alive.
Prey
items
were
usually
carried
away
or
eaten,
but
on
12
occasions
they
were
left
in
situ
after
they
had
stopped
moving.
Two
cats
(numbers
2
and
3,
Table
1)
used
cleared
patches
in
long
grass
to
stalk
field
voles
Microtus
agrestis
and
occasionally
bank
voles
Myodes
glareolus,
cat
6
adopted
a
sit-and-wait
strategy
to
pounce
on
house
mice
from
behind
dense
grass
or
shrub
cover,
while
cat
15
waited
at
entrances
to
the
burrows
of
long-haired
rats
Rattus
vil-
losissimus
and
actively
hunted
rats
after
they
emerged.
The
rabbit
specialist
cat,
number
4
(Table
1),
adopted
a
similar
strategy
of
sitting
near
entrances
to
warrens
and
pursuing
rabbits
that
emerged.
3.3.
Hypothesis
3:
are
preferred
prey
targeted
by
cats
irrespective
of
prey
density?
We
collected
329
cat
scats
at
Ryans
Reserve
(5–63
on
each
sampling
occasion)
and
271
at
Ethabuka
(5–35
on
each
sampling
occasion).
Analyses
of
these
scats
showed
that
cats
at
both
study
locations
ate
a
broad
range
of
prey,
with
native
small
mammals,
birds,
lizards
and
invertebrates
comprising,
variously,
5–83%
by
frequency
of
occurrence
on
any
given
sampling
occasion.
However,
rabbits
domi-
nated
the
diet;
they
were
represented
in
>50%
of
cat
scats
on
most
sampling
occasions,
falling
exceptionally
to
33%
by
frequency
of
occurrence
in
scats
at
Ryans
Reserve
and
to
8%
by
frequency
of
occurrence
at
Ethabuka.
Plots
of
rab-
bit
in
the
diet
of
cats
against
rabbit
abundance
suggested
that
cats
continued
to
consume
rabbits
even
when
rabbit
numbers
were
low,
with
this
effect
being
more
evident
at
Ryans
Reserve
than
at
Ethabuka
(Fig.
3).
The
curves
of
best
fit
in
each
study
location
were
second-order
polynomial
(quadratic)
relationships,
accounting
for
57%
of
the
vari-
ance
in
the
data
at
Ryans
Reserve
and
for
42%
at
Ethabuka
(Fig.
3).
These
models
indicate
that
rabbits
occurred
in
49%
of
cat
scats
at
Ryans
Reserve
and
25%
of
cat
scats
at
Ethabuka
when
rabbit
numbers
were
so
low
that
they
were
not
detected
in
spotlight
surveys
(Fig.
3a
and
b).
At
Ryans
Reserve
the
frequency
of
rabbit
in
the
diet
dropped
sharply
when
fewer
than
3.5
rabbits
were
observed
per
km

82
C.R.
Dickman,
T.M.
Newsome
/
Applied
Animal
Behaviour
Science
173
(2015)
76–87
Table
1
Hunting
success
of
individual
house
cats
Felis
catus
taking
four
different
categories
of
prey,
shown
as
the
%
of
successful
attacks
per
prey
category.
Numbers
in
brackets
represent
the
numbers
of
attacks
observed
on
prey
in
each
category.
The
total
number
of
observations
made
per
cat,
and
the
time
taken
to
make
the
observations,