Ecology of Red Maple Swamps in the Glaciated Northeast: A ...

Species composition of trees and shrubs in
swamps may be even more important than species
richness in eqlainirlg the local distributions of
certain small mammals. me majority of woody
plants in swamps, such as red maple, highbush
blueberry, and dewberries (Rubus spp.), produce
samaras or fleshy fruits, which provide abundant
food during summer and fall but are not available
for winter consumption. The stable year-round supply
of mast in upland oak-hickory forests is a major
factor promoting higher numbers of white-footed
mice in that habitat than in red maple swamps
(Getz 1961b; Batzli 1977; Breidling et al. 1983).
The southern red-backed vole (Fig. 7.7) was the
most abundant small mama1 species found in
Connecticut red maple swamps (Miller and Getz
1973, 1977a, b). This spies inhabits most forest
types in northem New England, but in southern
New England, where upland soils are generally
drier, it is apparexxtly restricted to forested wetland~.
GGtz (1%) showed that the red-backed vole
hm higher evaporative water loss and less efficient
kidx~eys than other srnall mammal species. As a
result,, it must live where standing wabr or succulent
foot5 items are readily available. In red maple
swamps, water is ~vaililblr voles in most of the
growixlg season. Even during exceeding1 y dry peri-
ods, title water t.zrLle is rls~~ally close enough to the
surface so that VOICR call gnin access to it by tuxulelling
along wind-lcmseucd t,rcae roots (hfiller and Getz
1972, 1973).
Witllin forested wc~t,lrtntfs, the amount, of escape
cover provided by low vegc:tation or debris strongly
influerxces tXxc; local. distribution and abundance of
red-backed voles. Miller and Cetz (1972, 1977b)
noted that vole abundance and survival rates were
nlcprkc.&y lower in arcas lacking escape cover, and
speculated that time lack of cover allowed higher
predation by diurnal avian raptors (e.g., red-shoddered
hawk).
Wildlife residing in seasonally flooded wetlands
must be able to adapt to widely fluctuating water
levels. Surface inundation in forested wetlands
during the spring and fall may make it difficult for
some srnall mammals to move about easily on the
forest floor. Water shrews and red-backed voles are
efficient swimmers and will enter water more readily
than other small mammal species (Getz 1967;
Godin 1977). White-footed mice are semiarboreal
and thus are able to retreat into trees to avoid
surface water. As noted earlier, lower food availability,
not seasonal flooding, appears to be responsible
for the lower densities of white-footed mice in
swamps compared with upland forests (Batzli
1977; Miller and Getz 1977b).
Medium-sized and Large Mammals
In western Massachusetts, black bears show a
strong habitat preference for wetlands from mid-
April, when they emerge from winter dens, until
mid-August (Elowe 1984). Although wetland composed
only an average of 11% of the territories of
seven radio-equipped female black bears, the bears
spent more than one-third of their time in spring
and summer in wetlands. Swamps were used most
heavily in spring, the season when food was most
scarce. Skunk cabbage was the most important
food at that time.
Throughout the North American range of black
bears, the majority of winter dens are located in
upland areas. Swamps are used as denning sites in
some areas of the eastern United States, but winter
flooding is a major hazard (Alt 19W, Smith 1985;
Hellgren and Vaughan 1989). In northeastern
Pennsylvania, Alt (1984) found that cub mortality
can be as high as 5% due to the flooding of dens by
frozen-ground runoff. The highest mortality occurred
in excavated or root-cavitv dens located in
swamps and selected by females during relatively
dry autumns; above-average precipitation during
fall reduced the selection of potentially dangerous
sites because of the presence of water at the time of
selection.
In the Northeast, beavers prefer to colonize lowgradient
perennial streams in small forested watersheds
(Iloward and Larson 1985), many of which
include red maple swamps. Red maple is a relatively
unimportant fwd species compared with al-
Fig. 7.7. Southern red-backed vole (Ckihrionomys ders, aspens, and wiliows
gapperi), one of the most ccmmon small mammals in
et 1951;
nodheastern red maple swamps. Drawing by R. Hodgdon and I-%unt 19661, but it may be of signifz-
Alexander:
cant vdue where these species are scarce and dur-