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TECHNICAL REPORT NO. 22
STATUS SURVEY OF FIVE FLORIDA MAMMALS
by
Stephen R. Humphrey,
Robert W. Repenning,
and Henry W. Setzer
Florida State Museum
University of Florida
Gainesville FL 32611
Supported by:
Jacksonville Endangered Species Office
U.S. Fish and Wildlife Service
2747 Art Museum Drive
Jacksonville, FL 32207
through the
Florida Cooperative Fish and Wildlife Research Unit
117 Newins-Ziegler Hall
University of Florida
Gainesville FL 32611
Research Work Order No. 16
February 1, 1986
TABLE OF CONTENTS
Introduction . . . . . .
Acknowledgments . . . . . .
Homosassa shrew, Sorex longirostris eionis . . .
Sherman's short-tailed shrew, Blarina carolinensis shermani
Pine Island rice rat, Oryzomys palustris planirostris .
Sanibel Island rice rat, Oryzomys palustris sanibeli .
Chadwick cotton mouse, Peromyscus gossypinus restrictus .
Conclusions . . . . . .
Literature Cited . . . . . .
2
3
. . 2
. . 3
. . 10
. . 15
. . 19
S . 28
. . 35
S . 38
STATUS SURVEY OF FIVE FLORIDA MAMMALS
Introduction
The purpose of this project was to determine the population status and
geographic distribution of five subspecies of mammals that occupy small areas
of coastal west-central Florida: Sherman's short-tailed shrew (Blarina
carolinensis shermani), the Homosassa shrew (Sorex longirostris eionis), the
Pine Island rice rat (Oryzomys palustris planirostris), the Sanibel Island
rice rat (Oryzomys palustris sanibeli), and the Chadwick cotton mouse
(Peromyscus gossypinus restrictus). A secondary goal was to evaluate the
subspecies' taxonomic status.
Concern about the future of these mammals is justified by their
restricted distributions, their genetic uniqueness, their habitat
requirements, and conversion of their habitats to human uses. Four of these
five subspecies are listed as Species of Special Concern by the State of
Florida (Florida Game and Fresh Water Fish Commission 1985); only the Pine
Island rice rat is not listed. All five subspecies are being considered for
possible listing under the federal Endangered Species Act (U.S. Fish and
Wildlife Service 1985). Additional research is needed to ascertain whether
the status of any of these taxa justifies listing and to provide biological
support for any management actions that might be proposed to assure the
subspecies' survival.
Acknowledgments
This study was made possible by the leadership of David Wesley and
Michael Bentzein of the U.S. Fish and Wildlife Service, the facilitation of
Franklin Percival of the Florida Cooperative Fish and Wildlife Research Unit,
and the cooperation of Don Wood of the Florida Game and Fresh Water Fish
Commission. We appreciate the interest and cooperation of numerous
individuals in the field, including Ralph Lloyd and Ron Hight of the J.N.
"Ding" Darling National Wildlife Refuge; Steve Phillips of the Sanibel-Captiva
Conservation Foundation; Ellison Hardee of the Department of Natural
Resources; Jeff Lincer of the Sarasota County Office of Environmental
Management; and J.P. Garner of the Homosassa Springs Attraction.
Homosassa shrew, Sorex longirostris eionis
Methods.--The type locality of the Homosassa shrew was identified from
the published description and verified by conversation with a long-time
employee of the Homosassa Springs tourist attraction. Sampling was done in
forest along the Homosassa and Crystal rivers (Figs. 1, 2). The latter site
was on the Williams Tract--State land managed by the Department of Natural
Resources, in habitat similar to the type locality. Sampling was done
continuously with five 25-m-long metal drift fences at each site, beginning
variously from 18 December to 9 March and checked through April 14. Drift
fences were buried several cm deep in the soil; to trap animals, a screen-wire
funnel trap was placed at each end and two pitfall traps (perforated coffee
cans) were buried flush with the surface along the middle. Additional
sampling was done intermittently at both sites with Sherman livetraps placed
in grids and lines from 18 December 1984 to 24 January 1985, for a total of
880 adjusted trapnights. Adjusted trapnights were computed as total
trapnights minus one-half the number of traps found sprung in the morning,
under the assumption that the average trap was sprung midway through the night.
Results.--The drift fences produced three Homosassa shrews, one from each
of three fences near the type locality (Table 1). None were found in the
Crystal River site. Twelve Blarina carolinensis also were captured, some from
each site. Shrews were captured only immediately after rain, presumably
because saturation of the soil forced shrew activity to the surface.
Therefore it is possible that capture success might have been higher during
the summer rainy season. The livetrapping produced 22 Peromyscus gossypinus,
2 Ochrotomys nuttalli, and 2 Sigmodon hispidus.
Taxonomy.--The Homosassa shrew was described on the basis of 10 specimens
Citrus County,
Florida
0 1o 2e
Kilometers
Fig. 1. Distribution of trapping sites at Homosassa Springs.
Crystal River, Florida
O 1 2
Kilometers
Fig. 2. Distribution of trapping sites at Crystal River.
Table 1. Shrews captured in hydric hammock near Homosassa
Springs and Crystal River, 18 December 1984 to 14 April 1985.
Fence Sorex Blarina Cryptotis Fence
Site nights longirostris carolinensis parva success
Homosassa Springs
0.025
0.008
0.043
0.020
0.010
Fence A
Fence B
Fence C
Fence D
Fence E
Crystal River
Fence F
Fence G
Fence H
Fence I
Fence J
0.000
0.024
0.000
0.027
0.027
Total 772 3 11 1 0.019
3 11
1 0.019
Total 772
7
taken in the swamp forest immediately adjacent to Homosassa Springs, Citrus
County (Davis 1957). At-the time, only 6 specimens of the southeastern shrew
from other areas of Florida were available to the author for comparison. We
examined 11 specimens of S. 1. eionis and 12 of S. 1. longirostris from
Florida. In our opinion, differentiation of the Homosassa subspecies is
valid. It has slightly larger teeth and the supporting bone structure is more
robust.
Survival Status.--The Homosassa shrew persists at the type locality.
Though considerable sampling effort was required to confirm its presence, the
data are inadequate to judge abundance of the population.
Distribution and Habitat.--The type locality is a very small circular
area contained within gravel walkways near the old entrance to the tourist
attraction. The new specimens reported here were taken near the perimeter of
the parcel of land containing the tourist attraction. The habitat of this
parcel, hydric hammock, resembles its original condition except that some of
it has been destroyed (Fig. 3). The type locality is now owned and operated
as a tourist attraction by Citrus County. The site was added to the CARL
(Conservation and Recreational Lands) acquisition list by the Florida Cabinet
in April 1985. The city and vicinity of Homosassa Springs have been developed
by conversion of hydric hammock, and this process is continuing, but
significant amounts of undeveloped forest remain.
A continuous tract of hydric hammock occurs along the Gulf coast from the
southern boundary of Pasco County north almost to Crystal River. After a
small discontinuity of slash pine flatwoods, the hydric hammock continues
north to Gulf Hammock and west nearly to Cedar Key. However, most of this
northern area was cleared and converted to pine plantation in the 1960's.
Fig. 3. ASCS aerial photos (upper, DCP-16C-58, November 1944; lower, A20
18017-374-75, April 1974) of Homosassa Springs. The town is on the right, and
the tourist attraction is on the left, where the road bends around the two
spring runs. The obvious habitats are hydric hammock on the left and slash
pine flatwoods on the right.
Like most terrestrial mammals, Sorex longirostris is not particularly
habitat-specific. The most detailed study on the ecology of this species,
conducted in the Dismal Swamp of Virginia, showed that the shrews occurred in
any type of forested wetland and avoided only uplands and marshes (Robert
Rose, unpublished). Comparably broad habitat use in Florida could mean that
the distribution of the Homosassa shrew might be much larger than documented.
If so, it might be separated from the range of S. 1. longirostris only by
upland topographic features like the Archer and Brooksville ridges.
Management.--Protection of habitat clearly is desirable. The obvious
target of such protection at present is the tourist-attraction parcel.
Secondary targets could be inferred but not supported by scientific evidence.
Research Needs.--Much more field work must be done to determine whether
the geographic range of this subspecies is as small as documented, or as large
as possible. Depending on the answer, the current rate of habitat loss would
be judged either alarming or not.
Sherman's short-tailed shrew, Blarina carolinensis shermani
Methods.--Because two subspecies were targeted in the Fort Myers area,
sampling was done in a variety of habitats ranging from marsh to pine
savanna. The vicinity of the type locality has undergone extensive suburban
and urban development, and we were unable to pinpoint its exact location. We
sampled several remnants of undeveloped oak woodland and drainage ditches
within one-half mile of the published coordinates, as well as similar habitats
far to the east and west (Fig. 4). Sherman livetraps were placed in lines or
grids with an inter-trap distance of 10 m. Rolled oats was used as bait.
Results.--Field work in North Fort Myers and Cape Coral failed to produce
any new specimens of Sherman's short-tailed shrew (Table 2).
Taxonomy.--Sherman's short-tailed shrew was described on the basis of 27
specimens (Hamilton 1955a). Because the original description made detailed
comparisons with the other Florida subspecies of short-tailed shrew, and
because few museum specimens of shermani have been collected since then, a
taxonomic review at this time would yield no new insights on the genetic
uniqueness of this population.
Survival Status.--Although we could not confirm the presence of the
population in the vicinity of the type locality, two specimens were collected
9 miles east of Fort Myers by staff of the Florida State Museum in 1981.
Therefore the population appears to survive, but there is no basis to judge
its status.
Distribution and Habitat.--Sherman's short-tailed shrew was described on
the basis of 27 specimens taken from a single locality near Fort Myers, Lee
County (Hamilton 1955a). The site was 1 mile north of the Edison Bridge
spanning the Caloosahatchee River and 0.25 mile east of U.S. Highway 41 (see
11
co
W
0
z
e-
LL
*0
SCO
z LL
Fig. 4. Distribution of trapping sites at North Fort Myers, Cape Coral,
Little Pine Island, and Pine Island.
Little Pine Island, and Pine Island.
Table 2. Small mammals captured on Pine Island, Little Pine Island, and the
adjacent mainland, 6 December 1984 to 18 January 1985.
Adjusted
trap Sigmodon Oryzomys Peromyscus Blarina Trap
Site nights hispidus palustris gossypinus carolinensis success
Pine Island
0.034
0.094
Grid A
Grid B
Little Pine Island
Grid C
Grid D
Line E
127.5
111
32
0.031
0.162
0.438
mainland (Cape Coral
Grid F
Line G
Grid H
Grid I
Line J
Line K
Grid L
Line M
Line N
Line 0
and North Fort Myers)
124
112
127
127.5
19.5
111.5
63.5
18
67
41.5
0.008
0.098
0.008
0.071
0.154
0.009
0.047
0.000
0.194
0.120
62 30 5
Total 1298
0 0.075
Fig. 5). Shrews were caught in drainage ditches and in tunnels made by
moles. Hamilton's sampling totaled 4,000 trapnights. Judging from the
unsuccessful attempts to collect more specimens at the type locality in this
study and in 1956 (Layne 1978), habitat conversion may be severe enough at the
type locality to have extirpated the population there. Collection of two
specimens 9 miles east of Ft. Myers in 1981 demonstrates that the subspecies
is distributed beyond the type locality, but no insight is available on the
extent of this range.
Like most terrestrial mammals, the short-tailed shrew has broad habitat
tolerances. In Florida it is known from several types of closed-canopy
forest, from hydric hammock upslope to mesic hammock.
Management.--Not enough information exists to know whether management is
needed nor what actions might help Sherman's short-tailed shrew.
Research Needs.--Much more field work must be done to document the
geographic range of this subspecies.
Fig. 5. ASCS aerial photo (DCT-1LL-152, February 1970) of North Fort Myers,
including sample sites H, I, and J. The Edison bridge and the older route of
U.S. Highway 41 are on the right.
Pine Island rice rat, Oryzomys palustris planirostris
Methods.--Sampling was in marshes and drainage ditches. The type
locality on Little Pine Island was near our grids C and D (Fig. 4). Because
we were unable to pinpoint the mainland site, we sampled several drainage
ditches within one-half mile of its coordinates (published in Hamilton 1955a
rather than in the type description [Hamilton 1955b]), as well as similar
habitats and marshland far to the east and west. Sherman livetraps were
placed in lines or grids with an inter-trap distance of 10 m. Rolled oats was
used as bait.
Results.--We captured 28 rice rats on Little Pine Island and 8 on the
mainland (Table 2, Fig. 4).
Taxonomy.--The Pine Island rice rat was described by Hamilton (1955b).
Though the locality for 12 of his specimens is given as Pine Island, Lee
County, details of the description actually refer to Little Pine Island.
Another specimen taken on the mainland, 2 miles north of Fort Myers, was
included in the type series. This treatment of the mainland specimen suggests
a wider distribution than implied by the common name of the subspecies. The
Little Pine Island specimens were captured in a garbage dump and an adjoining
Spartina patens marsh. Persistence of the insular population was confirmed by
staff of the Florida State Museum in 1981, when 3 specimens were captured.
We examined 15 male specimens of 0. p. planirostris and compared them
with 135 males of other subspecies from Florida and southern Georgia. Females
also were examined, but they were not used for statistical comparison because
of greater variation in body size than males. Canonical discriminant analysis
showed that planirostris is distinct from the mainland subspecies (0. p.
coloratus) but not from the Sanibel Island subspecies (0. p. sanibeli). In
the original description (Hamilton 1955b), the two island forms were
distinguished only by color. Color is seldom adequate alone as a basis for
distinguishing mammal taxa, because pelage color is highly variable and
affected strongly by chemicals and light in the environment, and by fumigants
in museum cabinets. The two island populations of rice rats live in
contrasting environments--freshwater marshes on Sanibel Island and
brackish-to-salt water marshes in the Pine Island area. Thus the two island
populations should be treated as one. The Gulf islands rice rat is slightly
smaller than the mainland coloratus and has a flat rostral profile rather than
a convex one. Although the original description (Hamilton 1955b) includes
mainland animals and hence indicates a non-insular distribution for the Pine
Island population, our analysis shows that the mainland population is
referable to 0. P. coloratus.
Survival Status.--This population is abundant in appropriate habitat.
Distribution and Habitat.--The entire center of Little Pine Island is a
mosaic of marsh and salt flats (see Fig. 6) that is suitable habitat for rice
rats. Presumably the entire area is occupied. In contrast, no Pine Island
rice rats have been collected on Pine Island proper. On Pine Island, suitable
habitat is a relatively narrow strip of marsh and salt flats between the pine
savanna and mangrove (see Fig. 6). Before it was altered by mosquito ditches,
this marsh was maintained by the combination of high tides in spring, summer
rains, and high tides again in autumn. This long perimeter strip is
inaccessible, and it has been inadequately sampled for small mammals by both
Hamilton (1955b) and this study.
Management.--Little Pine Island is owned by the state of Florida and
managed by the Department of Natural Resources as Charlotte Harbor State
Fig. 6. ASCS aerial photo (DCT-1LL-64, February 1970) of Little Pine Island
(right) and central Pine Island, including sample sites B, C, D, and E.
19 -- -
18
Reserve. The marshland of Little Pine Island is being invaded extensively by
paperbark tree (Melaleuca quinquenervia). Perhaps this is a result of
hydrologic changes resulting from mosquito ditches dug in the 1960's. Unless
this plant succession can be reversed, habitat quality for rice rats on Little
Pine Island may diminish considerably in the future. Much of the marsh
perimeter of Pine Island was ditched in the 1960's, and the extent of marsh
habitat was reduced by both direct drainage and subsequent invasion of woody
plants. The ditches themselves are now occupied by white mangrove
(Laguncularia racemosa), and the spoil banks are covered by Australian pine
(Casuarina equisetifolia). Probably habitat could be improved on both islands
by filling the existing mosquito ditches.
Research Needs.--The primary research needs are sampling adequate to
determine if rice rats live on Pine Island and finding a habitat manipulation
that will reverse the woody succession on Little Pine Island.
Sanibel Island rice rat, Oryzomys palustris sanibeli
Methods.--Sampling was done at a series of sites extending along the
interior marshland of Sanibel Island (Figs. 7, 8). Sites were selected
according to accessibility, habitat character, and property ownership.
Sherman livetraps were placed in lines or grids with an inter-trap distance of
10 m. Rolled oats was used as bait.
Results.--The Sanibel Island rice rat was widespread in the interior
wetlands of Sanibel Island (Table 3).
Survival Status.--This population is abundant in appropriate habitat.
However, the absolute amount of habitat has been reduced by drainage and
development.
Taxonomy.--The Sanibel Island rice rat was described on the basis of 11
specimens captured 4 miles west of the lighthouse on Sanibel Island (Hamilton
1955b), at a site now known as the Bailey Tract of the J. N. "Ding" Darling
National Wildlife Refuge (see Figs. 8, 9). All were taken in freshwater
marshes dominated by cattails.
We examined 7 male specimens of 0. E. sanibeli (plus 1 from Captiva
Island and presumably referable to this subspecies) and compared them with 142
males of other subspecies from Florida and southern Georgia. Females also
were examined, but they were not used for statistical comparison because of
greater variation in body size than males. Canonical discriminant analysis
showed that sanibeli is distinct from the mainland subspecies (0. E.
coloratus) but not from the Pine Island subspecies (0. p. planirostris). The
Captiva Island specimen was not distinct from sanibeli. In the original
description (Hamilton 1955b), the island forms were distinguished only by
color. Color is seldom adequate alone as a basis for distinguishing mammal
Fig. 7. Distribution of trapping sites on Sanibel Island.
Fig. 8. Detail of trapping sites on the Bailey Tract, Ding Darling National
Wildlife Refuge.
Table 3. Rodents captured on Sanibel Island, 29 October to 14 November 1984.
Adjusted
trap Sigmodon Oryzomys Mus Rattus Trap
Site nights hispidus palustris musculus rattus success
Line A 20.5 1 0 2 0 0.146
Line B 107 2 3 0 0 0.046
Line C 20 0 1 1 0 0.100
Grid D 24 0 2 3 1 0.250
Grid E 247.5 1 5 15 1 0.089
Grid F 96 2 0 10 0 0.125
Grid G 187.5 1 5 3 0 0.048
Grid H 47 0 0 2 0 0.043
Line I 21 0 0 0 0 0.000
Line J 24 1 0 0 0 0.042
Line K 21.5 1 0 0 0 0.047
Line L 24 0 0 0 0 0.000
Grid M 174.5 7 0 5 0 0.069
Grid N 60 3 0 1 0 0.067
Grid 0 185.5 8 4 13 4 0.156
Grid P 190.5 3 6 17 2 0.147
Line Q 22 0 1 2 0 0.136
Line R 56 0 0 0 0 0.000
Line S 19 3 2 0 0 0.263
Line T 30 3 2 2 0 0.233
Line U 87.5 5 2 6 0 0.149
Line V 32 0 0 >0* 0 0.000
Total 1697 41 33 82 8 0.097
* Present, recording error.
Fig. 9. ASCS aerial photo (DCT-ILL-70, February 1970) of central Sanibel
Island. The wildlife drive on the major dike through Ding Darling National
Wildlife Refuge is prominent in the upper left. The Bailey Tract is just
south of the heavily subdivided area at right. Just west of this area, the
channalized Sanibel Slough bisects the island, and a network of mosquito
ditches with adjacent spoil piles is evident. Marshlands are the lighter gray
areas between ridges of coastal hammock, which appear as parallel striations.
taxa, because pelage color is highly variable and affected strongly by
chemicals and light in the environment. The two island populations live in
contrasting environments--freshwater marshes on Sanibel Island and
brackish-to-salt water marshes in the Pine Island area. The pelage of
specimens we examined varied from silver to brown. Thus the two island
populations should be treated as one. The Gulf islands rice rat is slightly
smaller than coloratus and has a flat rostral profile rather than a convex one.
Distribution and Habitat.--This population is widely distributed on
Sanibel Island. In 1960, staff of the Florida State Musuem collected two rice
rats on Captiva Island, 1.5 and 2 miles north of the Sanibel-Captiva bridge,
in coastal hammock on the Gulf shore.
The current distribution on Sanibel Island includes a portion of the Ding
Darling National Wildlife Refuge. Other portions of the interior wetlands are
owned by private conservation organizations, including the Sanibel-Captiva
Conservation Foundation, The Nature Conservancy, and the Center for
Rehabilitation of Wildlife. However, the majority of the habitat is in other
private ownerships, and it could be expected to be developed for human
residences as time passes.
Sanibel Island is unique among barrier islands of the Gulf coast of the
United States in containing a meandering slough (the Sanibel "River", see Fig.
9), which drains the interior during high-water periods. Except for low,
wooded ridges, this interior basin supported marsh vegetation (Fig. 10)
dominated by cordgrass (Spartina patens) and sawgrass (Cladium jamaicensis).
This habitat was maintained by yearly flooding of rainwater and irregular
invasion by salt water from either extremely high tides or storm surges.
However, the character of this marshland has radically changed in the last 25
Fig. 10. Control-burned cordgrass marsh in the interior of Sanibel Island, on
property of the Sanibel-Captiva Conservation Foundation, near sample sites
G-L. This is prime habitat for the Gulf islands rice rat.
Fig. 11. Former marshland along the channalized Sanibel Slough, severely
impacted by altered hydroperiod. Whatever the climax association of the
obvious hardwood succession, this is no longer good habitat for rice rats.
years, as a result of three factors (U.S. Fish and Wildlife Service 1984).
First, in 1951, local residents plugged the outlet of the Sanibel Slough on
the east end of the island, impounding water in the eastern end of the basin
and isolating the impounded area from new inundations of salt water. Second,
in the 1950's and early 1960's, the Lee County Mosquito Control program
channalized the Sanibel River and built a system of ditches (see Fig. 9) and
stop-log water control structures that reduced the water table and completed
the impoundment of the interior wetlands. Third, the dewatered wetlands were
invaded by a combination of salt-intolerant native plants and aggressive
exotic plants, to form cattail marshes in the wettest places and dense
woodlands of buttonwood (Conocarpus erectus) and Brazilian pepper (Schinus
terebinthifolius) in the drier areas (Fig. 11). This habitat change has
drastically reduced the extent of wetlands and its carrying capacity for
wetlands wildlife.
Management.--A significant conservation action taken by the Sanibel City
Council on 25 July 1984 was establishment of the Interior Wetlands
Conservation District as a section of the Sanibel Comprehensive Land Use
Plan. This District is a 3,000-acre tract within the island's interior
wetlands. The legislation prohibits development within 200 feet of either
bank of the Sanibel River, limits the intensity of use of areas less than 3
feet in elevation, and provides guidelines for reducing environmental damage
where development is permitted. However, the area in which development would
be precluded is a narrow strip within the District. In 1985, the City of
Sanibel was moving to acquire some parcels in this zone.
If the original flora and fauna are to be retained, the interior wetlands
need to be burned to kill woody plants and flooded to favor the marsh
association. Although it can be debated whether fires caused by natural
agents were normal events, now they are the only means of setting back plant
succession that can be applied over large areas at low cost. Flooding should
simulate both the historic water levels and the fluctuating hydroperiod of the
slough. Human needs for water may preclude use of groundwater for this
purpose, but the alternative of actively restoring some of the pre-existing
drainage pattern by filling mosquito ditches should be carefully studied.
Burning, spraying with herbicide, and hand-removal of exotic woody plants on
Ding Darling NWR, on the Bailey Tract and at Grid E north of the highway
S-curve, have improved the habitat there for rice rats. The most recent
efforts suggest that burning alone may be the best approach. Similarly,
marshland at the Sanibel-Captiva Conservation Foundation has been burned with
good results.
Research Needs.--Before the highly modified marshlands of these islands
can be managed with known consequences to rice rats, experiments need to be
conducted to learn how their populations respond to habitat manipulation.
More field work is needed to determine if Gulf islands rice rats occur on
other islands around Charlotte Harbor, such as on North Captiva, Cayo Costa,
and Gasparilla islands.
Chadwick cotton mouse, Peromyscus gossypinus restrictus
Methods.--Sampling for the Chadwick cotton mouse was conducted on
Manasota Key in Sarasota and Charlotte Counties during 1-19 October 1985 and
16-23 March 1985. Sherman livetraps were placed in lines or grids with an
inter-trap distance of 10 m. Rolled oats was used as bait. Seven sites (Fig.
12) were sampled along the Key from a city park in Venice (Grid A) south to
Englewood Beach (Grid K). Other public lands sampled were Casperson Beach
County Park (Grid B) and Blind Pass Beach County Park (Grid I). Three
mainland sites (Grids C-E) also were trapped to obtain comparative data.
Results.--During the first sampling period, a total of 980.5 adjusted
trapnights on the Key resulted in no captures of Peromyscus gossypinus, though
three species of non-target rodents were captured (Table 4). On the mainland,
two of the three sites yielded P. gossypinus. During the second sampling
period, an additional 741 trapnights on the Key, distributed among Grids A, I,
and J, resulted in capture of only a single spotted skunk (Spilogale putorius).
Taxonomy.--The Chadwick cotton mouse was described on the basis of 15
specimens taken at Chadwick Beach, near Englewood, Sarasota County (Howell
1939). They occurred in the sea oats along the beach and in the adjacent
cabbage palm forest. No specimens of the Chadwick cotton mouse appear to have
been collected since the type series was taken. However, a taxonomic review
of this population might be interesting in view of the qualitative nature of
the comparisons in the type description. Because so few specimens of this
subspecies are available, such a review would require a major statistical
comparison with other subspecies in the region. In view of the apparent
extinction of the taxon, such an exercise would be strictly academic.
Survival Status.--The Chadwick cotton mouse appears to be extinct.
Manasota Key, Florida
0 1 2 34 5
I Kilometers
Kilometers
Fig. 12. Distribution of trapping sites on Manasota Key.
Table 4. Rodents captured on Manasota Key and the adjacent mainland, 1-19
October 1984 and 16-23 March 1985.
Adjusted
trap Mus Rattus Sigmodon Oryzomys Peromyscus Spilogale Trap
Grid nights musculus rattus hispidus palustris gossypinus putorius success
A
B
C
D
F
F
G
H
I
J
K
Total
127.0
121.0
90.5
45.5
122.0
121.5
171.5
120.0
318.5
638.0
104.0
1979.5
0.031
0.050
0.033
0.286
0.123
0.000
0.000
0.050
0.009
0.000
0.029
0.027
Distribution and Habitat.--The place name "Chadwick Beach" no longer
occurs on maps, but conversation with local residents and real estate
businessmen revealed its location to be near the southern end of the Key in
Englewood Beach. Manasota Key is a peninsula, not an island. However, the
primary habitat of this subspecies is essentially insular, because the coastal
forest is very narrow at the neck of the peninsula. The maritime forest is a
very narrow strip at the northern end of Manasota Key, becoming wider
southward. The forest edge is affected by the harsh coastal environment and
is composed only of cabbage palms, which are relatively tolerant of salt and
wind. At Grid A, only this narrow edge occurs. Where the forest widens
farther south, its interior reflects a successional history and is dominated
by live oaks (Quercus virginiana) and southern red cedar (Juniperus
silvicola). The greatest tree-species and structural diversity now occurs at
the southern end of Sarasota County, at and near Grid J (Fig. 13).
Cotton mice prefer closed-canopy forest, but as noted in the type
description of P. g. restrictus, cotton mice also occupy grassland such as sea
oats adjacent to coastal forest (Fig. 14). The sea oats strip along the coast
of Manasota Key has been reduced to a few remnants, mostly in publicly owned
parks dedicated to beach recreation. Landward, numerous remnants of the
forest remain, divided into many, small, privately owned parcels developed for
residences and vacation homes (Fig. 15). Some of the larger lots in Sarasota
County were developed by clearing vegetation for a house site but leaving
forest to buffer neighboring properties. The southernmost portion, in
Charlotte County, has been completely destroyed by human construction. In
view of the amount of forest remaining in Sarasota County, we were surprised
that no cotton mice appear to remain on Manasota Key. As has been suggested
Fig. 13. Coastal hammock
is most extensive.
on Manasota Key, at sample site J, where the forest
Fig. 14. Sea oats grassland seaward
Blind Pass County Park, Manasota Key.
of the coastal hammock at sample site I,
Fig. 15. ASCS aerial photos of Manasota Key. Upper row, Sarasota County
between sample sites H and I. Lower row, Charlotte County between sample
sites J and K. Left column, March 1957. Right column, February 1970. Photo
numbers, clockwise from upper left: DEW-2T-182, A20 12115 274-261, A20 12115
274-194, DEW-2T-174.
34
for other mouse populations on heavily settled coastlines, predation by the
large number of continuously distributed house cats (Felis cattus) associated
with the human residences may render the remaining woodlots uninhabitable by
cotton mice. It is conceivable but unlikely that a remnant population of
Chadwick cotton mice persists somewhere on Manasota Key.
Research Needs.--The only imaginable need for further research is
additional survey work in the hope of reversing our conclusion.
Conclusions
The conclusions of this study are summarized as follows:
Taxonomic Survival
Subspecies status status Distribution Habitat
Homosassa shrew Confirmed Not threatened Possibly insular Forested
but extensive wetlands
Sherman's short- Valid Not ascertained Extent unknown, Mesic to
tailed shrew may be declining hydric forest
Pine Island rice =sanibeli Not threatened Gulf islands Marsh
rat
Sanibel Island =planirostris Threatened Gulf islands, Marsh
rice rat declining
Chadwick cotton Moot Extinct Formerly insular Closed-canopy
mouse forest
The Homosassa shrew persists in the type locality but was not found in a
nearby tract of similar habitat. The immediate vicinity of the type locality
is buffered from development pressures by public ownership. The most
important information need is to extend the field search for other
populations. Although this subspecies is known only from a single site, the
species has broad habitat tolerances, so possibly its distribution could be
quite large. The subspecies is a valid taxon.
Sherman's short-tailed shrew was not located in the fragments of habitat
remaining around the type locality, so its distribution may be declining. The
area around the type locality has changed to suburban and urban habitat, and
further development of an infilling nature is continuing there. This shrew
was recorded east of Fort Myers in 1981, confirming survival of the population
and raising the possibility that its distribution could be much larger than
documented. The taxon appears to be valid, and few new specimens have been
taken since the original description. The existing information on the
subspecies' distribution and population status remains inadequate.
The Pine Island and Sanibel Island rice rats are distinctive from the
mainland form but not from each other, so they should be pooled as a single
subspecies. It also did and still may occur on Captiva Island. More field
work is needed to document the full distribution of this population, which may
include all islands with marsh or salt-flat habitat in the Charlotte Harbor
area. Probably the population should be termed the "Gulf islands rice rat",
and its survival status should be considered from this larger perspective.
Experiments are needed to determine how population densities respond to
habitat manipulation, and ways need to be found to reverse the successional
impacts of historical mosquito-ditching, channelizing, and diking of marshland.
The population on Pine Island is abundant in the marshes and salt flats of
Little Pine Island. This land is under State ownership, but the habitat is
rapidly being degraded by invasion of Melaleuca. Management action will be
required if this succession is to be reversed. Rice rats have never been
recorded on Pine Island. The potential habitat there has been severely
impacted by mosquito-ditching, and it has not been adequately sampled for rice
rats.
Rice rats remain abundant in the interior wetlands of Sanibel Island, but
this habitat has been severely impacted by drainage and plant succession.
Carrying capacity and probably distribution have been reduced considerably.
Portions of the population occur in Ding Darling National Wildlife Refuge and
on private land dedicated to conservation, so the potential exists to sustain
this segment of the population in perpetuity with appropriate management
programs. These should focus on burning to kill woody invaders and flooding
37
to restore historic hydrologic conditions.
The Chadwick cotton mouse appears to be extinct. Its taxonomic status
appears to be valid, but the point is moot. Its distribution was insular, in
the coastal forest and adjacent grasslands of Manasota Key. Its habitat has
been heavily impacted by development of human residences and thoroughly
invaded by house cats, which may make the remaining woodlots uninhabitable for
cotton mice. It is unlikely that further searches will reveal a remnant
population of this mouse.
Literature Cited
Davis, J.A., Jr. 1957. A new shrew (Sorex) from Florida. Amer. Mus.
Novitates 1844:1-9.
Florida Game and Fresh Water Fish Commission. 1985. Official lists of
endangered and potentially endangered fauna and flora in Florida.
Tallahassee. 24 p.
Hamilton, W.J., Jr. 1955a. A new subspecies of Blarina brevicauda from
Florida. Proc. Biol. Soc. Washington 68:37-40.
Hamilton, W.J., Jr. 1955b. Two new rice rats (Genus Oryzomys) from Florida.
Proc. Biol. Soc. Washington 68:83-86.
Howell, A.H. 1939. Descriptions of five new mammals from Florida. J. Mammal.
20:363-365.
Layne, J.N. 1978. Sherman's short-tailed shrew. Pp. 42-43 in J.N. Layne
(ed.), Rare and endangered biota of Florida. Vol. I. Mammals. Univ.
Presses of Florida. 52 p.
U.S. Fish and Wildlife Service. 1985. Endangered and threatened wildlife and
plants; review of vertebrate wildlife; notice of review. Federal
Register 50:37958-37967.
U.S. Fish and Wildlife Service. 1984. Bailey Tract management plan. File
document, Ding Darling National Wildlife Refuge. 20 p.
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