BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Sigmodon hispidus | Hispid Cotton Rat 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Diurnal and Annual Activity:  Some studies have suggested that hispid
cotton rats are mainly nocturnal, but activity has been observed at all
hours.  Activity patterns appear to be influenced by both biotic and
abiotic factors.  Hispid cotton rats are active year-round [6].

Breeding Season:  Hispid cotton rat populations usually exhibit a
bimodal breeding season, with peak litter production occurring in late
spring and in late summer-early fall [6].  Rose [67] reported
reproductive peaks in March and June for hispid cotton rats; 100 percent
of trapped females were pregnant from March through July, but none were
breeding in November and December.  They do not breed in the coldest
winter months.  In Kansas breeding is restricted to the frost-free
months [6].

Nest Building:  A nest is constructed by the female either on the ground
surface or in a burrow.  Nests are cup- to ball-shaped and woven of
grasses [6].  Hispid cotton rats in the northern parts of their range
make nests that are thicker and denser, but not larger, than those of
southern hispid cotton rats [58].

Gestation and Development of Young:  Gestation in hispid cotton rats
lasts approximately 27 days.  Litter sizes range from 1 to 15 young,
with larger litters more typical of northern populations and also of
late-season litters.  Neonates are well developed; they are mobile and
lightly furred but the eyes are not open.  The eyes open approximately
18 to 36 hours after birth.  Hispid cotton rats are weaned in 10 to 15
days and reach minimum adult size by about 41 days [7,68].

Productivity:  Some male hispid cotton rats are sexually mature by 60
days, some females are receptive by 30 to 40 days.  The earliest
recorded pregnancy was at 38 days [7,68].  Hispid cotton rats have been
noted as one of the most prolific mammals in the Southeast.  Females
bear two to several litters per year depending on latitude and local
weather [63].  Females mate within 24 hours of giving birth [6].

Longevity:  In Kansas remnant prairie very few hispid cotton rats were
recaptured after 8 months [15].

Population Fluctuation:  Hispid cotton rat populations are largely
sedentary; population density depends mainly on current reproductive
effort and not as strongly on immigration [29].  In Kansas remnant
prairie hispid cotton rat population density was highest in fall and
early winter and lowest in spring and early summer [15].  In the
northernmost parts of hispid cotton rat range, severe weather is
associated with rapid hispid cotton rat population declines and local
extinctions [43].  In Kansas most hispid cotton rat mortality was
associated with severe weather in March and April.  Populations in the
northern part of hispid cotton rat range experience dramatic declines in
the nonbreeding season.  In many areas local extinction is frequent
[52].  In Georgia hispid cotton rat spring abundance in old fields was
lowest following drought and extreme winter cold.  The reductions in
hispid cotton rat populations were associated with sharp declines in
vegetative biomass and cover [37].

Effects of Predation:  In Georgia a density of 15 hispid cotton rats per
acre was considered the predator-limited carrying capacity.  Mammalian
predators did not have a substantial effect on hispid cotton rat
population density.  At densities higher than 15 per acre mortality was
high; below 15 hispid cotton rats per acre predator-caused mortality was
low [55].  Schnell [55] concluded that when diverse and mobile predators
are present they are more important than food, social interaction, or
weather in limiting hispid cotton rat density.  

Also in Georgia, 1-acre field enclosures protected from avian predators
(covered with a net) were monitored for the effect of avian predators on
breeding hispid cotton rat populations.  The presence of the cover had
no effect on seasonal recruitment or spring-summer mortality; however,
autumn-winter mortality was greatly reduced with the cover in place.  It
was therefore suggested that avian predators are more important than
mammalian predators.  In addition, it was concluded that nonbreeding
(winter) populations suffer substantial losses from predation whereas
breeding populations are either able to compensate by replacing lost
individuals, are less vulnerable to predation, or both [64].


PREFERRED HABITAT : 
Hispid cotton rats occupy a wide variety of habitats within their range
but are not randomly distributed among microhabitats.  They are strongly
associated with grassy patches that have some shrub overstory and they
have little or no affinity for dicot-dominated patches [26,27].  Habitat
use and preference by hispid cotton rats usually appears to depend on
the density of monocots.  However, some studies are equivocal on the
importance of other vegetation [16].  For example, hispid cotton rats
may respond favorably to a high percentage of dicots in a stand if cover
remains optimal.  In Kansas hispid cotton rats increased on root-plowed
prairie that experienced an increase in the diversity and biomass of
early-successional forbs [19].  Also see discussion of Oklahoma savanna
in HABITAT-RELATED FIRE EFFECTS.

Male hispid cotton rats exhibit a lower degree of habitat selectivity
than females.  In Texas males were found on different habitat types
(grassy, shrubby, and mixed) approximately in proportion to
availability; female hispid cotton rats tended to choose mixed habitats
more often than expected based on availability [7].

Habitat use varies with season and breeding status.  In Texas grassy
areas with some shrubs were preferred in spring and areas with more
shrubby cover were preferred in fall [27].

Grassland Habitats:  In Kansas remnant prairie the preferred habitat of
hispid cotton rats has dense undergrowth and an upper layer of
protective vegetation such as big bluestem (Andropogon gerardii)/kochia
(Kochia scoparia)/annual sunflower (Helianthus annuus) [15].  Hispid
cotton rats prefer grassy clearings, croplands, overgrown fields, and
overgrown roadsides and right-of-ways [42].  In Kansas prairies hispid
cotton rats occur at relatively high abundance in ungrazed uplands and
sandy mixed-grass native prairie, but also prefer disturbed areas.
Kaufman and others [24] suggested that the use of disturbed areas was
probably important in the recent invasion of hispid cotton rats into
north-central Kansas from the northern presettlement limit of their
range in Oklahoma.  On Texas rangelands hispid cotton rats appeared to
respond to increased biomass of standing crop and increases in the
proportion of the standing crop in potential food plants such as
bristlegrasses (Setaria spp.).  Hispid cotton rat density was four times
greater on areas planted to exotic grasses including King Range bluestem
(Bothriochloa ischaemum) and buffel grass (Enchrus ciliaris) than on
native range dominated by windmill grass (Chloris spp.) and Texas
wintergrass (Stipa leucotricha) [19].

Succession in Grasslands:  In northeastern Kansas hispid cotton rats
occurred at high population densities in tallgrass prairie (dominated by
perennial grasses); population density declined to levels too low to
accurately estimate over 28 years of succession to brush and trees [14].
They are occasionally found in habitats dominated by early successional
grassland species (i.e., annual grasses and forbs) [9].

Woodland Habitats:  Hispid cotton rats occur in grassy areas or
early-successional habitats within open woods.  In the Southeast hispid
cotton rat population density increases with the density of broomsedge
(Andropogon virginicus) and other low growing plants, but declines with
succession to brush and trees [29].  In Texas pine-hardwood forests,
hispid cotton rats were captured most often in narrow streamside
management zones which have more light and thus more ground cover, and
slightly less often in wider zones [1].  In central Louisiana longleaf
pine-slash pine stands hispid cotton rats were captured in sawtimber,
sapling, and regeneration stands but not in pole-sized timber; stands
with surface cover were more likely to support hispid cotton rats.
Pole-sized timber is dense, little light reaches the ground, and surface
cover is minimal [46].  In Louisiana and Mississippi hispid cotton rats
were more numerous in cut than in uncut bottomland hardwoods.  They were
also more numerous in cottonwood (Populus spp.) plantations than in
uncut cottonwood stands [65].  In northern Georgia intensive site
preparation following clearcutting of pine-hardwood mixtures increases
forage production and increased numbers of small mammals (presumably
including hispid cotton rats) [11].

Importance of Climate:  In Colorado hispid cotton rats occupy semimoist
areas with abundant grasses and weeds and appear to be restricted to
relatively warm areas [39].  In New Mexico hispid cotton rats do not
occur regularly in areas with a mean annual temperature lower than 55
degrees Fahrenheit (13 deg C) and a growing season shorter than 180 days
[45].  In Trans-Pecos Texas hispid cotton rats occur at the warmer, low
elevations in areas of moderate to dense grassy cover [54].

When water and wastewater are added to baldcypress (Taxodium distichum
var. distichum) domes, small mammals including hispid cotton rat move to
peripheral areas that are drier.  The rising water tables favor marsh
rice rats (Oryzomys palustris) over hispid cotton rats [21].

Population Density:  Cameron and McClure [68] compiled reports of hispid
cotton rat population densities.  The mean hispid cotton rat population
density range for all studies was 5.3 to 31.1 rats per hectare.
Population density ranges in Texas include 1 to 14 rats per hectare in
coastal prairie, 17 to 84 rats per hectare in unmowed right-of-ways, 9
to 29 rats per hectare in old fields, 6 to 54 rats per hectare in
abandoned fields, and 0.7 to 5 rats per hectare in grass-pricklypear
(Opuntia spp.).  In Florida population density ranges include 0 to 24
rats per hectare in sand pine scrub, 2 to 47 rats per hectare in pine
flatwoods, and 27 to 94 rats per hectare in tropical hammock.  In Kansas
hispid cotton rat density ranges were 0.2 to 21 rats per hectare in
grassland [68]; the highest estimated density was 65.4 hispid cotton
rats per hectare in favored habitat [15].

Habitat Patch Size:  In a study of the effects of habitat patchiness on
movement, hispid cotton rats preferred only the largest patches which
were 165 feet by 330 feet (50 x 100 m).  Patches were established by
mowing strips between blocks of grasses.  Hispid cotton rats were
present in intermediate numbers on medium sized patches which were 39.6
feet by 79.2 feet (12 x 24 m), but were so scarce on the smallest patches
that their movement pattern could not be analyzed [10].

Home Range:  In Kansas remnant prairie the average annual home range of
adult male hispid cotton rat was estimated as 0.969 acre (0.39 ha) and
that of adult females as 0.543 acre (0.21 ha).  The greatest distance
traveled by an adult male was 330 feet (100 m) and by an adult female
was 250.9 feet (76.4 m) [15].  In Texas male hispid cotton rats also had
larger home ranges than females.  Home ranges were larger in summer and
winter than in spring and fall.  Home range size was positively
correlated with body mass and negatively correlated with population
density.  There was a relatively high degree of exclusivity (41%),
indicating intolerance of conspecifics, particularly of the same sex
[7].  In Texas hispid cotton rats found their original home ranges
(homed) from displacements of up to 5,000 feet (1,500 m).  Returns were
relatively high from displacements of up to 990 feet (300 m), suggesting
that hispid cotton rats are familiar with the area within that distance.
Hispid cotton rats released in areas with no cover homed better than
hispid cotton rats released in typical hispid cotton rat habitat [8].
Spencer and others [69] used site fidelity as a measure of an
individual's actual home range and concluded that hispid cotton rats
have both single-day and multiday site fidelity and therefore establish
true home ranges.


COVER REQUIREMENTS : 
On the southern Coastal Plain hispid cotton rats use gopher tortoise
(Gopherus polyphemus) burrows for shelter in sandhill scrub dominated by
longleaf pine, bluejack oak (Quercus incana) and sand post oak (Q.
stellata ssp. margaretta) [35].


FOOD HABITS : 
Hispid cotton rats are omnivorous, but the major portion of their diet
consists of green vegetation.  They occasionally consume insects and
other small animals [63].  Field observations of hispid cotton rat diet
indicate that preferred foods are the stems, foliage, and seeds of crop
and wild plants [42].  Golley [18] reported that in the Southeast,
perennial legumes and broomsedge comprised a large portion of the diet
of hispid cotton rats.  They also consumed roots and tubers.  In Texas
hispid cotton rat diets always included the lower green stems of grasses
(which are relatively low in nutritive value); raspberries (Rubus spp.),
privet (Ligustrum spp.) fruits, and leaves of fogfruits (Phyla spp.)
were consumed as available [50].


PREDATORS : 
Hispid cotton rats are preyed on by many birds and reptiles, and by
other mammals [63].  In Oklahoma hispid cotton rats were a major prey
item in the diet of Swainson's hawks (Buteo swainsonii) [3].  In central
Missouri hispid cotton rats comprised 19 percent of prey items in
red-tailed hawk (B. jamaicensis) nests [62].  Hispid cotton rat remains
comprised a substantial portion of short-eared owl (Asio flammeus)
pellets in Arkansas [59].  Hispid cotton rats were the third most
important prey item of red wolves (Canus rufus) in eastern Texas and
Louisiana [56].  In North Carolina bobcats (Lynx rufus) consumed
substantial numbers of hispid cotton rats [72].  Hispid cotton rats were
a minor item in the diet of Florida panthers (Felis concolor coryi)
[40].  In north-central Florida the only direct evidence of predation on
hispid cotton rats was the presence of hispid cotton rat remains in a
barred owl (Strix varia) pellet.  The authors also observed a corn snake
(Elaphe guttata guttata) killing a hispid cotton rat just after the rat
was released from a trap.  The snake apparently had been waiting on the
runway where the trap had been set [38].


MANAGEMENT CONSIDERATIONS : 
The hispid cotton rat is an economic pest in the Southeast where it
causes damage to sweet potato, corn, peanut, tomato, sugar cane, squash,
carrot, and cotton crops.  Hispid cotton rats also take northern
bobwhite (Colinus virginianus) eggs and chicks and sometimes reduce
northern bobwhite productivity [42,47,63].

In old fields abandoned for 3 years in Georgia, hispid cotton rats
consumed up to 2 percent per month of the standing crop of vegetation
when at peak population densities.  Since hispid cotton rats clip more
vegetation than they consume, they also accounted for 10 percent of the
monthly litter input. At lower densities hispid cotton rats are
relatively unimportant in consumption and litter production [36].

Hispid cotton rats are a reservoir for some human diseases including
rabies, Chagas' disease, and Venezuelan equine encephalitis [6].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Sigmodon hispidus | Hispid Cotton Rat