Journal of Mammalogy, 92(1):101–110, 2011
Spatial ecology of a ubiquitous Australian anteater, the short-beaked
echidna (Tachyglossus aculeatus)
STEWART C. NICOL,* CÉCILE VANPÉ, JENNY SPRENT, GEMMA MORROW,
AND
NIELS A. ANDERSEN
School of Zoology, University of Tasmania, Private Bag 5, Hobart, Tasmania 7001, Australia (SCN, JS, GM, NAA)
Centre for Reproduction and Genomics, Department of Anatomy & Structural Biology, University of Otago, P.O. Box
56, Dunedin 9054, New Zealand (CV)
Present address of CV: Population and Conservation Genetics Group, Instituto Gulbenkian de Ciência, Rua da Quinta
Grande 6, 2780-156 Oeiras, Portugal
* Correspondent: [email protected]
The only specialized ant-eating mammal in Australia and New Guinea is the egg-laying short-beaked echidna
(Tachyglossus aculeatus), and this single species occurs throughout Australia in a wide range of habitats.
Despite the diversity of habitats and density and distribution of prey species, home-range sizes throughout
Australia seem remarkably similar. We radiotracked echidnas in a population in Tasmania over a 13-year period
and calculated home-range sizes using the fixed kernel method and the minimum convex polygon method. No
relationship was found between body mass and home-range size, and mean annual home-range size of males
(90% kernels) was 107 ha 6 48 SD, twice that of females (48 6 28 ha). Male home ranges overlapped
considerably and also overlapped with those of several females. The echidna follows the pattern seen in many
solitary eutherian mammals: both sexes are promiscuous, and males have larger home ranges than females.
Echidnas show a high degree of home-range fidelity but can make rare excursions out of their normal area.
Hibernating echidnas move between shelters during their periodic arousals, resulting in home-range sizes
similar to those of the active period. Consistent with their very low metabolic rate, echidnas have home-range
sizes considerably smaller than predicted for carnivorous or omnivorous mammals. Examination of data from
other ant-eating mammals shows that as a group anteaters not only have smaller than predicted home ranges but
they depart significantly from the normal relationship between home-range size and body mass.
Key words:
ecology
anteaters, home range, kernel, mating system, monotremes, myrmecophagy, short-beaked echidna, spatial
E 2011 American Society of Mammalogists
DOI: 10.1644/09-MAMM-A-398.1
The concept of home range, first defined by Burt (1943) as
that area traversed by an individual in its normal activities of
food gathering, mating, and caring for young, is central to our
understanding of the ecology of terrestrial vertebrate species.
The consensus that has emerged from a large number of
studies on eutherian mammals is that body size is the main
determinant of home-range size because of the close link
between body size and energy demand, with diet, energy
availability, climate, and behavior explaining some of the
residual variation (McNab 2002). In a comprehensive analysis
of the available mammal data Kelt and Van Vuren (2001)
found a positive relationship between mass and home-range
size for carnivores, omnivores, and herbivores, with significant differences between the 3 trophic groups: carnivores had
larger home ranges than omnivores of the same mass, which in
turn had larger home ranges than herbivores.
Myrmecophagous mammals—those that specialize in eating
ants and termites—have low rates of metabolism, and McNab
(1966) has argued that this is because they are dependent on a
low-quality food source that is patchy in both space and time,
and they have a low foraging efficiency. Ant-eating mammals
from a range of taxa have relatively small home ranges (Joshi
et al. 1995, 1999). In Australia and New Guinea the only
mammalian specialist anteater is the egg-laying short-beaked
echidna (Tachyglossus aculeatus). The other Australian
specialist myrmecophage, the smaller (0.5 kg) marsupial
numbat (Myrmecobius fasciatus), feeds exclusively on termites and now is restricted to small populations in southwest-
www.mammalogy.org
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Vol. 92, No. 1
TABLE 1.—Home ranges of adult echidnas from various regions of Australia. MMA: modified minimum area method; MCP: minimum convex
polygon; ‘‘Direct’’: plotted positions were enclosed in a hand-drawn smooth outline taking into account geographic boundaries; Anderson
analysis: a nonparametric method using the Fourier transform (Anderson 1982).
Study area
Subspecies
Estimation method
Period
11 months
Multiyear
Western Australian wheatbelt
Snowy Mountains
acanthion
aculeatus
Kangaroo Island
multiaculeatus
MMA
‘‘Direct’’
Anderson analysis (95%)
‘‘Direct’’
Kangaroo Island
multiaculeatus
MCP
Southeastern Queensland
aculeatus
MCP
Multiyear
1 year
Home range
(ha; X̄ 6 SD) (n)
65
42
58
55
6
6
6
6
17
20
31
14
(16)
(11)
(11)
(7)
24.8 6 1.7 (15)
70.3 6 11.1 (15)
50 6 27 (7)
Range (ha)
24–192
24–68
23–110
42–85
13.2–33.6a
55.8–90.2b
21–93
Reference
Abensperg-Traun (1991)
Augee et al. (1992)
Rismiller and McKelvey
(1994)
Rismiller and McKelvey
(2009)
Wilkinson et al. (1998)
a
Females during early lactation.
b
Females during late lactation.
ern Western Australia (Friend 2008). In New Guinea echidnas
occur both in coastal areas and highlands (Van Deusen and
George 1969), and in Australia echidnas are nearly ubiquitous
in their distribution (Augee 2008; Griffiths 1968). The diet of
the short-beaked echidna consists largely of ants and termites,
with occasional other soil invertebrates. In general, it appears
that termites are preferred in arid areas, but in temperate
southeastern Australia the preference is for ants, although
significant amounts of termites are eaten at times (Griffiths
1978). In Tasmania the diet is reported to consist nearly
entirely of ants (Griffiths 1989), and we have seen no evidence
of termites in scats from Tasmanian echidnas (J. Sprent, pers.
obs.). Ants live in smaller colonies than termites and have a
larger proportion of their mass as nondigestible chitinous
skeleton (McNab 1984), and hence the distribution and density
of resources will differ for animals primarily feeding on
termites and those eating mainly ants. Milewski et al. (1994)
have argued that specialized termite- and anteaters are smaller
in Australia than in southern Africa, despite similarities in
climate and soils, because overall availability of food
resources is significantly lower in Australian ecosystems. If
home-range size is determined primarily by availability of
food relative to metabolic requirements, within Australia
differences in the proportions of ants and termites in echidna
diets could result in differences in spatial ecology. However,
studies on home ranges of echidnas in a variety of environments, including the Western Australian wheatbelt (AbenspergTraun 1991), the Snowy Mountains (Augee et al. 1992),
Kangaroo Island (Rismiller and McKelvey 1994), and southeastern Queensland (Wilkinson et al. 1998), despite using
different estimation methods, have given reasonably consistent
mean home-range sizes of approximately 40–65 ha (Table 1).
These studies did not show any difference in home-range
size between male and female echidnas. Echidnas are
considered to be solitary (Griffiths 1978), and in solitary,
sparsely distributed eutherian mammals home ranges of males
are typically larger than those of females, because female
foraging ranges are minimized for energetic efficiency and
males benefit from searching widely for potential mates
(Clutton-Brock 1989; Sandell 1989). The lack of an
observable difference between sexes in these previous studies
of echidna home ranges is thus surprising, but sample sizes
were relatively low, and in his study of T. a. acanthion in the
Western Australian wheatbelt Abensperg-Traun (1991) did not
distinguish between adult males and females.
Since 1996 we have been studying a population of shortbeaked echidnas in southern Tasmania (Nicol and Andersen
2002, 2007b) and have collected a large amount of data on
distribution and movements of individuals. We investigated
variation in home-range sizes within this population to address
a number of questions. Are home ranges of Tasmanian
echidnas the same size as those of mainland echidnas, despite
significant differences in diet? Is there any relationship
between the mass of an individual and the size of its home
range? Is there any difference between home-range sizes of
males and females? Are there seasonal changes in home-range
use associated with reproduction and hibernation? Do
echidnas remain in the same home range over their adult
life? How do echidna home ranges compare with those of
other anteaters?
MATERIALS AND METHODS
Study species.—Short-beaked echidnas have been divided
into 5 subspecies, principally on the basis of their degree of
hairiness, hind-limb claw length, and geographic distribution
(Griffiths 1978). Home-range sizes have been measured in 3
of these subspecies, T. a. multiaculeatus, which is restricted to
Kangaroo Island (South Australia); T. a. acanthion, which
occurs across the arid zone; and T. a. aculeatus, from
southeastern mainland Australia (Table 1). The Tasmanian
subspecies, T. a. setosus, is considerably hairier than mainland
echidnas and shows a number of life-history differences.
Tasmanian echidnas all undergo an annual deep hibernation
and show differences from other subspecies in mating
behavior, time spent by the mother in the nursery burrow,
and the length of the lactation period (Morrow et al. 2009;
Nicol and Andersen 2007b).
Field procedures.—The study was carried out on a 12-km2
site (42u289S, 147u149E) on a grazing property in the southern
midlands 50 km north of Hobart, Tasmania. The study site
consists of improved and native pasture with areas of
February 2011
NICOL ET AL.—ECHIDNA SPATIAL ECOLOGY
Eucalyptus amygdalina woodland on sandstone (Harris and
Kitchener 2005). The site has variable topography with
altitudes ranging from 200 to 400 m above sea level with
numerous sandstone outcrops, caves, creeks, and gullies.
Between February 1996 and the end of December 2008,
759 days were spent in the field—an average of 1 day per
week—with animals being monitored up to 3 times per week
during the breeding season (June–September). Animals found
while driving around the property were caught by hand,
weighed, and scanned with a hand-held radiofrequency
identification reader (Destron Fearing, South St. Paul,
Minnesota). Echidnas that had not been captured previously
had a passive integrated transponder tag (LifeChip; Destron
Fearing) injected subcutaneously. Capture location was
determined using a hand-held global positioning system
receiver (GPSmap 76CSx; Garmin International Inc., Olathe,
Kansas). Sex was determined by the presence or absence of a
spur on the ankle. Juvenile echidnas of both sexes have a
sheath-covered spur, which in males loses the sheath to
become an adult spur, but females lose the spur entirely. Our
classification of animals was validated in the reproductive
season by the presence of a palpable penis bulge in males, and
in females by a developing pouch and entry into a nursery
burrow. In any year up to 20 echidnas had a radiofrequency
radiotransmitter (Bio-Telemetry Tracking, St. Agnes, South
Australia) glued to the spines of the lower back, allowing them
to be located using a hand-held receiver. These animals were
subsequently located by driving to a location where a strong
signal was detected using an omnidirectional whip antenna
(Telonics Inc., Mesa, Arizona) mounted on the vehicle and
then tracked on foot using a hand-held folding yagi antenna
(Sirtrack Ltd., Havelock North, New Zealand). Global
positioning system coordinates, body mass, reproductive
condition, any reproductive activity, evidence of hibernation,
and other details of the location and animal activity were
recorded in a database. Two of the male and 7 of the female
echidnas used in this study had temperature data loggers
implanted in the abdominal cavity for periods of 1–10 years
for a study of hibernation (Nicol and Andersen 2002).
This work was carried out under permit from the Tasmanian
Department of Primary Industries, Water & Environment, and
the University of Tasmania Animal Ethics Committee, and
complies with the Tasmanian and the Australian Code of
Practice for the Care and Use of Animals for Scientific
Purposes (2004) and meets the guidelines approved by the
American Society of Mammalogists (Gannon et al. 2007).
Home-range calculations.—Echidnas can occupy the same
shelter continuously for long periods during hibernation (Nicol
and Andersen 2007a) or if in a nursery burrow. To avoid
temporal autocorrelation (Kernohan et al. 2001), if the same
position was recorded for an individual on consecutive
occasions it was used only once for home-range analysis.
Home-range sizes were estimated using the kernel method
(Worton 1989), and to allow comparison with previous
studies, also by using the minimum convex polygon (MCP)
method (Mohr 1947). Unlike the MCP method, which results
103
in considerable and unpredictable biases (Börger et al. 2006),
the kernel method can account for multiple centers of activity
(Kernohan et al. 2001; Powell 2000) and is less affected by
changes in the spatial resolution of the data (Hansteen et al.
1997). We adopted the fixed kernel method, as recommended
by Seaman et al. (1999). Smoothing parameter of kernels was
evaluated using the reference method (href). No consensus
exists in the literature about whether this or the least-squares
cross-validation method (hlscv) is the best method for homerange estimates (Blundell et al. 2001), and the accuracy of the
2 methods is similar (Börger et al. 2006). Although the href
method tends to over-smooth multimodal distributions (Seaman and Powell 1996), it has the potential merit of being more
conservative than the hlscv method (Bowman and Azzalini
1997). We estimated both the 90% (k90) and the 50% (k50)
kernel areas, as recommended by Börger et al. (2006), the
50% kernel area being used as a measure of the core area, or
preferred part of the home range (Cavalcanti and Gese 2009;
Cimino and Lovari 2003).
To evaluate the appropriate number of locations for
unbiased estimates of home-range size we used an incremental
analysis (Kernohan et al. 2001) based on the assumption that
home-range estimates reach an asymptote with an adequate
sample size (McLoughlin and Ferguson 2000). Thus we
generated a graph of k90 probability values against the
number of positions for a number of individuals for which the
number of available positions was greater than 40 and
identified the point at which the gradient of the slope changed
(Stickel 1954). The asymptote was usually achieved after
approximately 20 locations. Hence, for this study we set 20
locations as the minimum necessary to estimate home-range
areas, except for seasonal home ranges for which we had low
sample sizes (8 locations minimum). Following Burt (1943)
we discarded positions corresponding to excursions outside
the normal home range (i.e., here defined as isolated positions
.1 km from the center of the normal home range). To
evaluate the validity of this approach we used analysis of
covariance to investigate the relationship between home-range
estimates and the number of locations, using sex as the
categorical predictor.
For each individual, when enough positions were available
(n . 20), we estimated both annual home-range size and
home-range size for all years pooled. For each individual and
each year, if enough positions were available for the 2
compared periods (n . 8 for each period), we also estimated
home-range sizes during the hibernation period (based on
positions for which the individual was found hibernating), the
nonhibernation period (based on positions for which the
individual was not found hibernating), and during the mating
season (i.e., June–September—Morrow et al. 2009), and
nonmating season (i.e., the remaining part of the year) in
males.
Statistical analysis.—Statistical analyses were performed
using R 2.7.1 software (R Development Core Team 2006),
Statistica 6.1 (Statsoft, Tulsa, Oklahoma), and statistiXL 1.7
(http://www.statistixl.com). Home-range sizes and home-
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JOURNAL OF MAMMALOGY
range overlap indices were estimated using the kernel.area
function and the kerneloverlap function, respectively, implemented in the adehabitat R package (Calenge 2006). Homerange figures were drawn using the Home Range Extension
(Rodgers and Carr 1998) in ArcView GIS 3.3.
When sample variances for home-range measures differed
significantly between males and females (based on the F-test
for equality of variances), t-values for comparisons between
sexes were calculated using a t-test for unequal variances. For
differences between reproductive and nonreproductive years
in females, and differences between seasons within years (i.e.,
hibernation period versus nonhibernation period, and mating
season versus nonmating season in males) at the individual
level, we used paired t-tests. Home-range and mass data were
both normally distributed (Shapiro–Wilk test), and linear
models were used to test for the relationship between annual
home-range size or annual core area and maximum annual
body mass. To control for repeated measures of the same
individuals the identity of individuals was entered as a random
factor in mixed models. Model selection was performed using
the Akaike information criterion corrected for small sample
size (AICc), as recommended by Burnham and Anderson
(2002) for sample size , 40. The best model was the model
with the smallest AICc value. However, when the difference
between AICc values of 2 competing models was ,2, we used
the criterion of parsimony, selecting the simpler model
(Burnham and Anderson 2002). We used a backward
procedure by fitting 1st the more complicated model (i.e.,
including the effects of sex, mean body mass, and their
interaction), then removing the interaction, then removing the
additive effect, and finally, removing the main effects of
factors. We used the ‘‘lme’’ function (included in the ‘‘nlme’’
R 2.7.1 package) for fitting mixed-effects models (Pinheiro
and Bates 2000). We also tested the possibility that annual
home-range size or annual core area might be correlated with
mean body mass using a Spearman’s rank correlation
coefficient (rs) and by pooling the data from the 2 sexes, as
in the study of Wilkinson et al. (1998). Unless otherwise
stated, data are shown as mean 6 SD.
RESULTS
Animal captures.—Between February 1996 and December
2008 we tagged 214 echidnas on the property: 100 females, 78
males, and 36 individuals whose sex was not known. Fifty-five
echidnas were juveniles when 1st found. The total number of
resident echidnas on the study site is not known; echidnas are
very cryptic, and during this study the mean time between 2
consecutive sightings for individuals that were not being
radiotracked was 364 6 315 days (range 5 2–1,291 days, n 5
111), and 75 echidnas were observed only once. Overall we
collected a total of 3,750 locations (points), with the number
of observations per individual animal ranging from 1 to 238. A
total of 20 locations was obtained for 35 adult individuals,
and mean radiotracking period for these was 8.0 6 3.8 years
(range 5 1–13 years). Mean masses of these echidnas differed
Vol. 92, No. 1
(t33 5 2.15, P 5 0.039) by sex: males 3.81 6 0.47 kg (n 5 9),
and females 3.44 6 0.43 kg (n 5 26). Maximum masses did
not differ (t33 5 1.13, P 5 0.19) by sex: males 4.57 6 0.64 kg
(n 5 9), and females 4.25 6 0.62 kg (n 5 26).
Effect of calculation method on home-range estimates.—For
the pooled (multiyear) data, k90 values varied from 14 ha for a
juvenile male (not included in this analysis) to 177 ha for an
adult male. The smallest home range for a reproductively
mature echidna was 23 ha for an adult female. The
corresponding core areas (k50) were 4.7 ha for the juvenile
male and 69 ha for the adult male, and 7.7 ha was the smallest
core area for a reproductively mature animal.
We used a minimum of 20 positions to estimate home-range
size, and for the multiyear home ranges the mean number of
points (n) was 56. For home ranges calculated with 20
locations (Table 2) we found no relationship between the
number of points and the k90 and k50 size (k90, n: F1,33 5
3.06, P 5 0.09; sex: F1,33 5 35.73, P , 0.0001; k50, n: F1,33
5 0.67, P 5 0.42; sex: F1,33 5 29.24, P , 0.0001), whereas a
strong relationship existed between MCP size and n (n: F1,33
5 42.97, P , 0.0001; sex: F1,33 5 35.06, P , 0.0001).
Sex differences in home-range size.—When home ranges for
adult males and females for all years were pooled, mean
home-range size was 70.7 6 7.6 ha (n 5 35). For home ranges
calculated from data points over several years (pooled data)
mean home ranges, core areas, and MCPs (Table 2) were
larger for males than for females (k90: t10.7 5 4.69, P 5
0.001; k50: t10.2 5 4.09, P 5 0.002; MCP: t10.45 3.59, P 5
0.005). Annual home-range sizes were slightly smaller than
when all years were pooled, but again, mean individual home
ranges, core areas, and MCPs were larger for males than for
females (k90: t8.1 5 3.03, P 5 0.016; k50: t19 5 3.58, P 5
0.002; MCP: t7.6 5 3.01, P 5 0.018).
Correlation of home-range sizes with body masses.—When
controlling for repeated measures of the same individuals, the
best mixed linear model explaining the variation in annual
home-range size or the variation in annual core area was the
model including only the sex effect (AICc 5 296.1 and 236.1,
respectively). The constant model (AICc 5 304.9 and 243.4,
respectively) and the model including the additive effect of
maximum annual body mass and sex (AICc 5 298.6 and
238.9, respectively) explained less of the variation in these
parameters. Although annual home ranges and annual core
areas were significantly larger in males than in females,
maximum annual body mass had no effect on annual homerange size or annual core area. In addition, when we pooled
the 2 sexes, the correlation between maximum annual body
mass and annual home-range size or annual core area was not
significant (rs 5 0.10, n 5 21, P 5 0.60 for both home ranges
and core areas).
Variation in individual home-range size between years and
between seasons.—We were able to investigate interannual
variations in home-range size for only 5 females and 2 males.
Home-range sizes sometimes varied considerably between
years for individual females (the maximal interannual
difference in home-range size ranged from 2.8 to 93.8 ha, X̄
97.3 6 42.2 (9)
34.9 6 21.0 (26)
25.3–68.6
7.7–35.8
42.6 6 15.9 (9)
15.9 6 7.5 (26)
56.6 6 27.7 (7)
23.1 6 14.2 (14)
12.5–55.7
5.6–37.0
35.3 6 16.1 (7)
15.4 6 9.5 (14)
Male 107.0 6 47.6 (7) 34.8–163.8
Female 48.0 6 27.7 (14) 16.7–104.3
50% kernel
90% kernel
Annual
MCP
21.3–89.6
7.4–54.1
130.1 6 36.2 (9) 85.5–176.9
50.1 6 22.4 (26) 23.0–106.9
50% kernel
90% kernel
Pooled
MCP
56.4–199.5
13.4–97.2
NICOL ET AL.—ECHIDNA SPATIAL ECOLOGY
TABLE 2.—Home ranges calculated as 90% kernels for adult Tasmanian short-beaked echidnas, showing values calculated for individual years and for multiyear (pooled) data. 50%
kernels are used as a measure of core area. Values are shown as means 6 SD (n) and ranges. Only home ranges based on 20 points (locations) have been included. Kernels were
calculated using the reference method (href). MCP: minimum convex polygon.
February 2011
105
5 28.5 ha, n 5 5) and males (range 5 31.8–53.4 ha, X̄ 5
42.6 ha, n 5 2). The proportion of overlap between 2 annual
home ranges of individuals ranged from 22% to 100% in
females (X̄ 6 SE 5 75% 6 5%, n 5 18 overlap measures)
and from 53% to 95% in males (X̄ 6 SE 5 66% 6 5%, n 5 8
overlap measures). For 5 echidnas (1 male and 4 females) in
which we had sufficient data points over 10 years, the mean
overlap of 90% kernels for the 1st and last 2 years of the 10year period was 57% 6 10% (X̄ 6 SE).
We found no difference between the home ranges or core
areas of individual females in years in which they reproduced
and years in which they did not (k90: t6 5 1.63, P 5 0.15;
k50: t6 5 1.83, P 5 0.12). Individual males had significantly
smaller home ranges (65% 6 32%) but not core areas (73% 6
35%) during the period October–April, when they are not
reproductively active, than during the June–September mating
period (k90: t8 5 2.87, P 5 0.021; k50: t8 5 2.28, P 5 0.052).
Despite this, the home ranges for males during the nonmating
period were significantly larger than female home ranges
(k90: t9.0 5 2.86, P 5 0.021; k50: t8.8 5 2.63, P 5 0.052). No
difference was found between home-range sizes calculated for
all locations for individual animals while they were hibernating compared to when they were active (k90: t10 5 1.17, P 5
0.27; k50: t10 5 1.35, P 5 0.21).
Apart from 1 major excursion a female echidna tracked for
13 years moved apparently randomly within the home range
over a 13-year period (Fig. 1A). This excursion occurred
entirely during the hibernation and mating period. After a brief
bout of hibernation on 4–6 April, she was observed to be
active in her core area on 8 April. Ten days later she was
found hibernating 3.1 km away. During the subsequent
2 months she hibernated in this new area, moving hibernacula
during her periodic arousals (Fig. 1B). On 17 June she was in
a mating group with a single male, 1.5 km from her core area,
before reentering hibernation, and then returned to her core
area during a subsequent arousal.
Home-range overlap between individuals.—We observed a
high degree of overlap of home ranges, with some male home
ranges being completely within the home ranges of others and
with up to 80% overlap of some females. However, because
we were able to track only a maximum of 20 individuals
within a year, and these were spread across the study area, we
are unable to estimate overlap among all individuals in the
population. During the 2008 breeding season (6 June–5
September) and the following 2 months we tracked 6 adult
males and 7 females in a 3.5-km2 section of the study area (see
Fig. 2 for k50 for these 13 animals). Only 3 of the females and
2 of the males met our criterion of 20 points for accurate
determination of home ranges (mean number of points for
females 5 16, range 5 8–29; mean number of points for males
5 19, range 5 7–35); however; 90% and 50% kernels for all
of these animals fell within the range of annual values reported
above. As with the entire data set, male k90 and k50 (Fig. 2)
were significantly larger than those of females (k90: t6.2 5
3.77, P 5 0.009; k50: t5.5 5 3.85, P 5 0.008). Overlap
between males was very high (Fig. 2A), with the smallest core
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JOURNAL OF MAMMALOGY
FIG. 1.—Home range and body temperature of female echidna
5D5E. A) Home range based on 145 independent data points over
13 years. Also shown are the kernel isopleths up to 90% (63.5 ha),
with the area (18.1 ha) within the 50% isopleth (the core area)
shaded, and the minimum convex polygon (73.7 ha). Light-shaded
symbols are locations where she was hibernating. Scale markers:
1 km. An additional 52 points are not shown nor included in the
home-range calculations because the animal was at the same location
as for the preceding observation, either because she was hibernating
or in a nursery burrow. The 6 numbered points were excluded from
home-range calculations. These were consecutive locations recorded
during a major excursion outside the home range in 2002. On 8 April
she was active in the core area; 16 April hibernating at 1, 3.1 km
away; 30 April–7 May hibernating at 2; 24 May–12 June hibernating
at 4; 5 June hibernating at 4; 17 June in mating group at 5; 19 June
hibernating at 6; 21 June hibernating in core area; and 28 August in
nursery burrow. B) Body temperature during 2002. Numbers 1–6
correspond to the same numbers in A. Horizontal lines indicate times
where the echidna was observed to be in the same location.
Hibernation began in late March and continued until early August.
The total distance between locations during that period was 5.2 km.
area lying entirely within the core of another male, but female
cores tend to be more evenly spaced (Fig. 2B). Core ranges of
most females were overlapped by 3 or 4 males. Three of the
reproductively active males had typical male home ranges
(114 ha from 9 points, 119 ha from 16 points, and 124 ha from
13 points, respectively, for k90), but male 5115 had a very
small home range (35 ha from 35 points), although he was
found in a mating group.
DISCUSSION
Initially, we decided that the 90% kernel home range gave a
result that visually seemed to best delineate the area where we
would find the animal. This subjective judgment is supported
by the analysis of Börger et al. (2006), who found the kernel
method to be greatly superior to the MCP method, with the
Vol. 92, No. 1
FIG. 2.—Core areas (50% kernels) of A) 6 male and B) 7 female
echidnas radiotracked in the same 3.5-km2 section of the study site in
2008. Heavy outlines show animals that were reproductively active
that year; others hibernated through the mating season, although they
had been reproductively active in previous years. Small oval at the
bottom of the female ranges and the range above it are 2 cores for the
same animal. Seven more males and 2 females were found in mating
groups within these ranges. For the females shown the smallest core
area (k50) was 6.9 ha, and the corresponding home range (90%
kernel) was 21 ha (n 5 21 data points). The largest female core area
and home range were 15.1 ha and 55.5 ha, respectively (n 5 13 data
points). For males the smallest core area was 11.7 ha, and the
corresponding home range was 34.5 ha (n 5 35 data points). The
largest male core area was 53.5 ha, with a home range of 129.9 ha (n
5 7 points). Overlap among males is very high; most females are
overlapped by 3 or 4 males. Scale markers: 1 km.
most unbiased home-range estimator being provided by the
90% isopleths. This is supported by our analysis showing a
strong correlation between number of data points and the size
of the MCP, but not with k50 or k90. The difference between
the methods is illustrated in Fig. 1A, which shows 145
independent locations for a female echidna over 13 years and
the kernel isopleths up to 90% and the MCP. The kernel
method clearly provides a much better description of spatial
ecology of this animal than does the MCP method.
Echidnas showed considerable home-range fidelity over
long periods. The mean proportion of overlap between annual
home ranges among individuals was .60%, and .50% over
9 years. This supports previous reports that adult echidnas are
faithful to their home ranges and probably spend their entire
adult life within the same home range (Abensperg-Traun
1991; Augee et al. 1992). Echidnas remain in the same home
range up to 16 years in the Australian Capital Territory,
10 years on Kangaroo Island (Griffiths 1989), and at least
4.5 years in the Snowy Mountains (Augee et al. 1992). The
detailed information from the female we tracked for 13 years
illustrates this high degree of home-range fidelity, which is
consistent with reports of adult echidnas returning to their
home range after having been moved several kilometers
(Rismiller and McKelvey 1994).
The lack of any difference between home-range size of
hibernating and nonhibernating echidnas is initially surprising.
Although they are described as semifossorial and females raise
the young in a nursery burrow, echidnas do not hibernate in a
burrow but in a range of natural shelters. Most commonly at
our field site these were basal tree hollows, hollow logs, and
log piles, but echidnas also hibernated under rocks, in piles of
February 2011
NICOL ET AL.—ECHIDNA SPATIAL ECOLOGY
leaves or decaying wood, in grass-tussocks, or sometimes
simply buried in the soil. During the hibernation season
echidnas might relocate to another shelter during their periodic
arousals, which we have suggested can represent a form of
behavioral thermoregulation (Nicol and Andersen 2007a).
Echidnas do not feed during these periodic arousals, and their
use of the same home-range area during hibernation cannot be
related to food requirements. Instead it probably reflects their
familiarity with their home range and the availability of
suitable refuges, which they also use when active. It also
seems likely that one of the factors that determine the size of
the home range is the availability of shelters.
In our Tasmanian population male home ranges were more
than twice as large as female home ranges. Although this
result differs from previous findings where the data sets were
quite small (Augee et al. 1992; Rismiller and McKelvey 1994;
Wilkinson et al. 1998), in each of these studies the largest
adult home range was of a male and the smallest of a female.
Despite the differences in calculation method, when data from
these earlier investigations are analyzed collectively, male and
female home ranges differ significantly (Mann–Whitney U 5
35, n1 5 9, n2 5 16, P , 0.05).
The very large differences in home range we observed
between males and females cannot be attributed to differences
in body mass, because sex differences in mass, although
significant, are very small. In this study the male : female mass
ratios were 1.09:1, reflecting the extremely low degree of
sexual dimorphism in this species. This small difference is
further confounded by an annual mass variation of up to 35%,
which is why in our analysis of the effects of body mass on
home range we used the maximum annual mass. However,
even using this measure, mass did not account for any of the
differences in home range within and between sexes.
As in previous studies (Abensperg-Traun 1991; Augee et al.
1992) considerable overlap existed among echidna home
ranges, but because it is not practicable to determine the
number of echidnas in a particular area the number of
overlapping ranges cannot be estimated with any certainty.
However, females have smaller home ranges that tend to be
dispersed more uniformly, whereas males have large home
ranges that overlap very substantially.
Because males have similar diets to females (J. Sprent, pers.
obs.), if home ranges of females are determined by metabolic
requirements, and males have mass-specific field metabolic
rates similar to those of females, males have home ranges that
are on average more than twice as large as is required to supply
them with adequate food. The echidna appears to follow the
pattern seen in solitary eutherian mammals (Clutton-Brock
1989) and carnivorous marsupials such as spotted-tail quolls
(Dasyurus maculatus—Glen and Dickman 2006), with female
home range being determined by food resources and males
having larger home ranges to maximize mating success. This is
consistent with our observations on the mating system of
Tasmanian echidnas (Morrow et al. 2009; Morrow and Nicol
2009): both sexes are promiscuous, and males aggregate around
females, competing for mating opportunities.
107
Because females in noncooperative species such as the
echidna must rear young alone, their reproductive success will
be correlated closely with the amount of energy they can
allocate to reproduction. Thus, echidna females would be
expected to follow a behavioral tactic that maximizes their
chances of securing food resources for reproduction and
survival. Based on hourly observations over blocks of several
days, Rismiller and McKelvey (2009) found that the area used
by mothers during late lactation was 3 times that during early
lactation (the first 45–55 days). The metabolic demands of
early lactation are very low (Schmid et al. 2003), and although
field metabolic rates have not been measured during late
lactation, they could triple (Nicol and Andersen 2007b).
Although this suggests an increase in foraging area in line with
metabolic demands, during early lactation Kangaroo Island
echidnas forage with the young in the pouch, unlike
Tasmanian mothers that stay in the nursery burrow with their
young for the first 40 days (Morrow et al. 2009). Thus, the
smaller home range during early lactation in Kangaroo Island
echidnas could be due to the mother being encumbered with
the young in the pouch and needing to stay reasonably close to
the refuge of the nursery burrow rather than simply a
reflection of food requirement.
Previous studies on the spatial ecology of the short-beaked
echidna have used a variety of methods to estimate homerange size (see Table 1), so that comparisons between studies
should be treated with some caution. We have used the annual
MCP for this comparison, and bearing in mind the above
caveats and the limitations of the MCP method, the findings of
the various studies appear surprisingly concordant; female
home ranges showed no significant difference between studies
(Kruskal–Wallis: x23 5 4.11, P 5 0.25). This is surprising if
female home ranges reflect an optimal feeding strategy,
because prey densities are likely to vary significantly between
these regions. In all mainland sites, except the Snowy
Mountains, mound-building termites comprise a significant
proportion of the echidna diet (Abensperg-Traun 1988;
Griffiths 1978). Tasmania has no mound-building termites
(Watson and Abbey 1993), and nests of common ants such as
Iridomyrmex spp. do not reach the large size seen on the
mainland (Shattuck 1999). Thus, in most mainland Australian
sites food will have a much more clumped distribution, and
home-range sizes should be affected by this, overall food
availability, and other variables such as habitat, climatic
conditions, and predation pressure (Brashares and Arcese
2002; Curtis and Zaramody 1998; Sandell 1989; Wauters and
Dhond 1992). Apart from the variable quality of some of the
comparative data, a possible explanation for the failure to
observe differences in home-range size in echidnas from
different habitats is that echidna population density varies with
habitat quality and food density, but home-range size stays
relatively constant. This is consistent with the proposal that
home-range size is an inherent species property, but population density is a more flexible parameter reflecting ecosystem
state (Makarieva et al. 2005). Although echidnas are solitary,
no evidence exists of agonistic or aggressive interactions when
108
JOURNAL OF MAMMALOGY
FIG. 3.—Log–log plot of home ranges (ha) as a function of mass
(kg) for adult ant-eating terrestrial mammals. All home ranges have
been calculated using the minimum convex polygon (MCP) method.
Ranges for males (black) and females (gray) are shown separately. A
value for the predominantly termite-eating aardwolf has been
included for comparison. Circles: echidnas, pooled MCP data from
this study. Up triangles: Cape pangolin (Manis temminckii), data from
Heath and Coulson (1997), 3 males and 3 females, 100% MCP. Star:
aardwolf (Proteles cristata), data from Skinner and Van Aarde
(1986), 1 female, 100% MCP. Down triangles: giant anteater
(Myrmecophaga tridactyla), data from Medri and Mourão (2005), 3
males and 1 female, 100% MCP. Squares: aardvark (Orycteropus
afer), home ranges from Taylor and Skinner (2003), 2 males and 2
females, 95% MCP; masses estimated from Milewski et al. (1994).
Diamonds: sloth bear (Melursus ursinus), data from Joshi et al.
(1995), 12 females, 13 males, 100% MCP. Solid line: regression
through all data (except single aardwolf point): log home range (ha)
5 0.612 (6 0.304 SE) log mass (g) + 1.78 (6 0.45 SE); F1,8 5 4.06,
P 5 0.08. Dotted lines are from the regressions calculated by Kelt
and Van Vuren (2001): upper line represents carnivores and lower
line, omnivores.
foraging animals come into close proximity, and it is likely
that density is dependent on food availability. Unfortunately,
in a cryptic species such as the echidna densities are more
difficult to measure than is home-range size.
The allometric equations for mammalian home-range sizes
derived by Kelt and Van Vuren (2001) predict a home-range
size (MCP) of 280–440 ha for carnivores of similar mass to
echidnas or 130–180 ha for an omnivore. Both predicted
values are considerably larger than the annual MCPs
calculated for male and female echidnas. This is consistent
with the low basal metabolic rate and field metabolic rate of
this species, and more generally of anteaters larger than 1 kg
(McNab 1984; Nicol and Andersen 2007b). Fig. 3 shows
home-range sizes from the literature of male and female
terrestrial anteaters larger than 1 kg, plotted against body
mass, along with our data from the echidna. For comparison
with other studies, including the review of Kelt and Van Vuren
(2001), we have used MCP values in this graph. Although
aardvark home ranges are given as 95% MCP this should have
a very small effect when plotted on a log scale, and the much
Vol. 92, No. 1
smaller than expected home range of this species is probably
due to very fecund fungus-culturing termites making up a
significant proportion of their diet (Milewski et al. 1994). The
slope of the regression line of this log–log plot (0.61) is much
lower than the mean slope of 1.23 found for 73 carnivore
species (Kelt and Van Vuren 2001), or for 45 omnivore
species (1.21), and is not significantly different from 0. This
could be simply an artifact of the small sample size, but it is
consistent with large anteaters not only having lower basal
metabolic rates than other mammals, but also as their body
size increases, metabolic rate falls farther below the predicted
level (McNab 2000).
The apparent lack of a relationship between body mass and
home-range size in anteaters could be due to a combination of
factors. Biomass of ants is very high compared with that of the
prey of other carnivores, energy expenditure of anteaters is
constrained by the maximum rate of prey intake (McNab
2000) rather than prey density, and larger anteaters will take in
a larger proportion of nonfood items such as soil. What is not
known is what proportion of available ant biomass is harvested
by anteaters and how this might vary with habitat quality. The
overall pattern that emerges is that space use by anteaters does
not follow the pattern seen in other trophic groups.
ACKNOWLEDGMENTS
We thank all who have assisted us in the field over the course of
this study, particularly D. Lovell, A. Reye, M. Richards, U.
Rosebrock, J. Schmid, C. Vedel-Smith, and R. Wallace, and are
grateful to the McShane family for allowing us continued access to
their property. Financial support was provided by the Australian
Research Council, the University of Tasmania Institutional Research
Grants Scheme, the National Geographic Committee for Research
and Exploration, and the Holsworth Wildlife Research Endowment.
CV was supported by a Lavoisier postdoctoral research fellowship
from the French Ministry of the Foreign Affairs.
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Submitted 7 December 2009. Accepted 6 August 2010.
Associate Editor was Madan K. Oli.