BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 38, PT. 11(6)


to be due to the larger body size of male opossums (means 2.73 vs. 2.08 kg) and
consequently greater energetic needs (Harestad and Bunnell 1979; Reiss 1988).


 Home Range and Movement


 The minimum convex polygon has often been criticized for its sample-size bias,
sensitivity to extreme locations, linear borders, and because it may include large
unused areas (Jennrich and Turner 1969; Dixon and Chapman 1980). In the present
study, however, unused areas consisted mostly of lakes and wet prairie which could
easily be excluded (resulting in MCPcorr). Extreme locations were very rare and did
not represent a serious bias. The harmonic mean isopleths, on the other hand, are
related to the intensity of use and can define home ranges of any shape while being
largely insensitive to extreme locations (Dixon and Chapman 1980). However,
although the limits of the 95% isopleths roughly followed the distribution of data
points, the model was not able to closely delimit the areas of activity, and it could
include large unused areas while excluding particular location points. This makes the
method difficult to use in quantitative studies of habitat use (Ryser 1990). HM95 were
also in most cases larger than convex polygons, the difference being considerable in
cases with clumped location points. The same effect was also observed by Spencer and
Barrett (1984). Additionally, a closer examination of the results showed that HM95
were only slightly less sensitive to varying samples sizes than were MCPs (Ryser
1990).
 Therefore, I consider the corrected minimum convex polygon the most reliable
home range size estimate. With average values of 64.4 and 141.6 ha for females and
males, respectively, they are larger than values reported by Gillette (1980) from
Wisconsin (females: 51 ha, n=9; males: 108 ha, n=5) and by Allen et al. (1985) from
Georgia (females: 22 ha, n=5; males: 78 ha, n=2). However, these were based on 95%
convex polygons and a modified minimum area method, respectively, so possibly
underestimated home range sizes compared to this study. Sunquist and Eisenberg
(1993) found a similar mean home range size (58.7 ha, n=18) for female opossums on
the Ordway preserve. Values based on earlier capture-recapture studies (see Gardner
1982) can not be considered comparable to those of radio-tracking studies.
Quantitative data on nightly movements of opossums are equally rare. Allen et al.
(1985) and Sunquist et al. (1987, for D. marsupialis), both using 2-hour tracking-
intervals, reported values of 1278 (males) and 1026 m (females), and 1376 (males) and
1025 m (females), respectively. Seidensticker et al. (1987) reported values of 1137 to
1550 m depending on sex and season. The opossums in Florida thus tended to travel
farther in search of food, which corresponds to the possibly larger home range sizes
and may reflect a lower overall food density in the study area. The notion that
differences in space use are correlated with habitat productivity is supported by the
finding that the proportion of sandhills and former agricultural lands, areas of


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