RYSER: VIRGINIA OPOSSUMS (DIDELPHIS VIRGINIANA) IN FLORIDA


 Home Range


 Home ranges varied greatly in size, ranging from 8 to 564 ha (Table 3). Male
home ranges were on average about twice the size of female home ranges (MCP:
t44=3.25, p<0.01), irrespective of the method of calculation. HM95 tended to yield
greater values than convex polygons (MCP): Means differed by 10 to 15% (t44=0.31
and 0.53 in males and females, respectively, both ns), and in 82% of all cases
individual HM95 were larger than the corresponding MCP. Factors influencing
individual home range size were examined by means of a partial correlation analysis
(Table 2). In males, home range size tended to be positively influenced by habitat (see
method for definition), body size, and number of locations. In females, none of the
examined factors exhibited a coefficient significantly different from zero.


 DISCUSSION

 Activity


 Opossums were strictly nocturnal and, outside mating seasons, none was found
active before sunset or after sunrise. Most opossums left their dens at dusk and stayed
active for a varying period of time before reentering a den, usually well before dawn.
Consequently, the portion of active animals increased rapidly after dusk and reached
its highest level from 2000 h to 0200 h before gradually declining to zero. McManus
(1971) studied activity patterns in outdoor cages and found a similar curve in spring
and summer. However, the increase in activity was slower, and no more than 85%
were active at any time. In the present study, average nightly duration of activity
ranged from 7.85 to 9.33 hours, depending on season, sample, and sex. Seidensticker
et al. (1987) recorded average values of 8.23 to 10.95 hours, depending on season and
sex, but with no significant differences among the groups.
 Activity of opossums showed a temperature-dependence in two directions. At
nightly lows below about 80C, activity decreased linearly with decreasing temperature,
whereas above this threshold, activity tended to decrease with increasing temperature.
Decreased activity at low temperatures has been reported before in several studies.
Gillette (1980) reported that activity of opossums in Wisconsin decreased rapidly as
temperatures dropped below freezing, and that opossums did not leave their dens at
temperatures below -150C. Fitch and Sandidge (1953) and Fitch and Shirer (1970)
found that opossums in Kansas stayed in dens for several days during extremely cold
weather and that they sometimes foraged during the daytime after such cold periods.
With activity starting to decrease already at 80C and, as predicted by the regression,
ceasing altogether at -30C, opossums in Florida seem to react more sensitively to cold
temperatures than opossums in areas with harsher climates.