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2007 SOUTHEASTERN NATURALIST 6(2):259–270
Translocation of Swamp Rabbits in Southern Illinois
Angela M. Watland1,2, Eric M. Schauber1,*, and Alan Woolf1,3
Abstract - Habitat of Sylvilagus aquaticus (swamp rabbits) in Illinois has been
reduced and fragmented due to human land use. Translocation may enable swamp
rabbits to colonize isolated habitat patches. We live-trapped and translocated 9 male
and 8 female swamp rabbits to unoccupied habitat in southern Illinois in January and
February 2004. Eight of 17 translocated rabbits died within 7 days after release.
However, mortality rates appeared to drop rapidly over time after release. Predators
killed at least 10 of 14 rabbits that died. For conserving swamp rabbits, translocation
success is limited by poor live-trapping success and high levels of post-release
predation. Intense live-trapping along with predator control in release sites may be
necessary to make translocation a viable management strategy.
Sylvilagus aquaticus Bachman (swamp rabbit) is a representative species
of bottomland hardwood forests, occurring primarily in swamps, river bottoms,
and lowland areas (Chapman and Feldhamer 1981). The swamp rabbit is
a valued game species in portions of its range (Allen 1985), which extends
from the Gulf coast of Mexico, in Alabama, Louisiana, and Mississippi,
northward to include portions of Oklahoma, Tennessee, Kansas, Missouri,
Illinois, and Indiana, and eastward from eastern Texas to western South
Carolina (Allen 1985, Chapman and Feldhamer 1981, Hall and Kelson 1959).
However, population declines and restricted distributions of swamp rabbits
have been noted in Missouri (Korte and Fredrickson 1977), Kentucky (Sole
1994), Indiana (Mumford and Whitaker 1982), Arkansas (Sealander and
Heidt 1990), and Illinois (Kjolhaug 1986).
Historical records indicate that swamp rabbits have occurred in riparian
habitats throughout much of southern Illinois (Cockrum 1949, Layne 1958,
Nelson 1909). However, swamp rabbits appear to have become less common
in recent times, with a more restricted distribution than historical accounts
indicated (Kjolhaug et al. 1987). Remaining swamp rabbit populations and
their bottomland hardwood forest habitats are distributed patchily, clustered
in the extreme southern portion of the state along the Cache, Mississippi, and
Ohio rivers and along a few interior rivers and their tributaries (Barbour et
al. 2001, Kjolhaug et al. 1987, Woolf 1998). Habitat loss and fragmentation
of bottomland hardwood forests due to land-use practices, like logging and
conversion to agriculture, are most likely the principal causes of the restricted,
patchy distribution of swamp rabbits in Illinois and other areas in
the northern portion of their range.
1Cooperative Wildlife Research Laboratory and Department of Zoology, Southern
Illinois University, Carbondale, IL 62901. 2Current address - The Nature Conservancy,
146 East Main Street, Abingdon, VA 24210. 3Deceased. *Corresponding
author - email@example.com.
260 Southeastern Naturalist Vol. 6, No. 2
Eighty percent of the historically forested acreage of the Mississippi
alluvial floodplain has been cut for timber, converted to agriculture, or cleared
for development. The 4.8 million ha of Mississippi alluvial bottomland
hardwood wetlands that existed in 1937 had been reduced to 2.1 million ha by
1977 (Creasman et al. 1992). The remaining bottomland forests in Illinois are
highly fragmented, having generally small patch sizes (Twedt and Loesch
1999), and typically lack dry upland areas for rabbits to move to during
frequent flood events (Kjolhaug 1986). Loss and fragmentation of habitat
result in reduced population sizes, which increase the probability of extinction
by demographic and environmental stochasticity (Burkey 1995). The
extensive habitat loss and fragmentation of bottomland hardwood forests,
specifically in Illinois, has most likely concentrated swamp rabbits in isolated
habitat patches and subsequently increased vulnerability of populations to
stochastic events, predators, and other dangers (Conaway et al. 1960, Korte
and Fredrickson 1977, Toll et al. 1960). This decline in habitat and risk to
populations causes concern among natural resource professionals about the
status of swamp rabbits in Illinois (Barbour et al. 2001).
Because rabbits generally do not disperse long distances (Chapman and
Trethewey 1972, Richardson et al. 2002, Shields 1960), translocation represents
a potential approach to maintaining connectivity among remaining
bottomland hardwood patches and allowing recolonization of suitable habitat
from which swamp rabbits have become extinct. Several reintroductions
of lagomorph species have occurred as part of recovery or restoration efforts
(Calvete and Estrada 2004, Calvete et al. 1997, Faulhaber 2003, Hays 2001,
Letty et al. 2005, Swanson 2002, USFWS 1993, Williams et al. 2002). These
reintroductions have enjoyed varying degrees of success. In some cases, as
in reintroductions of Sylvilagus palustris hefneri Lazell (Lower Keys marsh
rabbits) and Sylvilagus bachmani riparius Orr (riparian brush rabbits), survival
in reintroduced populations has been similar to that of established
populations (Faulhaber 2003; L.P. Hamilton, Endangered Species Recovery
Program, California State University , pers. comm.). In contrast, Calvete et
al. (1997) reintroduced Oryctolagus cuniculus Linnaeus (European rabbits)
in Spain and observed 61% mortality during the first 10 days post-translocation.
Letty et al. (2005) also observed high mortality (39% within first 10
days) of translocated European rabbits in France. However, both Calvete et
al. (1997) and Letty et al. (2005) observed improved survival once an initial
critical period following release had passed. Calvete and Estrada (2004)
found that heavy cover and removal or exclusion of predators increased
survival of translocated rabbits.
For swamp rabbits, predation is likely to be an important limitation on the
success of translocated populations. Even in established populations, predation
can be an important cause of mortality. Kjolhaug (1986) found that
predation accounted for 83% of documented deaths in one swamp rabbit
population. Predator species known to kill swamp rabbits include Bubo
virginianus Gmelin (Great Horned Owl), Mustela vison Schreber (mink),
2007 A.M. Watland, E.M. Schauber, and A. Woolf 261
Lynx rufus Schreber (bobcat), and Canis latrans Say (coyote). Other documented
predators of Sylvilagus species include Felis sylvestris Linnaeus (feral
cats), Canis familiaris Linnaeus (domestic dogs), and several species of
hawks and owls (Williams et al. 2002). Massengill and Smith (1989) monitored
the fates of 10 swamp rabbits introduced to a wildlife management area
in Tennessee, and 7 were killed by predators within 6 weeks after release.
The goals of this project were to assess the feasibility of translocation as
a restoration strategy for swamp rabbits in southern Illinois, and offer
recommendations for similar restoration projects. To do so, we identified
suitable but unoccupied sites in southern Illinois where swamp rabbits could
persist, habitats could be managed in the future, and landowner cooperation
could be secured. After translocating swamp rabbits to the chosen site, we
evaluated short-term success through post-release monitoring.
Study Site Description
We captured swamp rabbits for translocation at Horseshoe Lake Conservation
Area (HLCA), a state-owned natural area in Alexander County, on the
southern tip of the state at the confluence of the Mississippi and Ohio Rivers.
This site was previously trapped for swamp rabbits and is also the location of
annual pellet-count transects for swamp rabbit monitoring (Woolf and
Barbour 2002). Land cover in Alexander County is characterized by 36.3%
cropland, 8.1% grassland, 31.5% forest/woodland, 14.5% wetland, and
2% urban, with 7.5% open water (Luman et al. 1996). Dominant overstory
vegetation included Taxodium distichum Rich (cypress)-Nyssa aquatica
Linnaeus (tupelo) swamp, with adjacent areas consisting of Populus spp.
(cottonwood) and Platanus occidentalis Linnaeus (sycamore). Dominant
understory species included Salix spp.(willow), Ilex decidua Walter (deciduous
holly), and herbaceous vegetation.
Woolf and Barbour (2002) identified 111 patches, covering 55,591 ha, of
suitable but unoccupied swamp rabbit habitat in their historical range in
southern Illinois (Barbour et al. 2001). Among these 111 patches, we focused
on 2 major watersheds, the Little Wabash and Wabash River watersheds, which
were not currently occupied by swamp rabbits, but contained large blocks of
suitable habitat. Based on habitat patch area and quality, as well as landowner
cooperation, we selected our primary release site along the Little Wabash River
and north of county road 1250N in Wayne County (UTM coordinates
397280N, 4255096W; Fig. 1). This 120-ha site had recently undergone timber
stand improvement (selective logging) through cooperation with the Illinois
Department of Natural Resources (IDNR) and, at the time of release, consisted
of early-successional forest with thick piles of slash and occasional thickets of
Arundinaria gigantea Walter (giant cane) along the river. Permanently flooded
areas were patchily distributed throughout the site. No sign of swamp rabbits
262 Southeastern Naturalist Vol. 6, No. 2
was found when bottomland hardwood patches in this area were searched in
1985 and 1995 (A. Woolf, unpubl. data). Wayne County is located in the
southeastern part of Illinois and consists of 457,696 acres. Land cover of
Wayne County is characterized by 62.4% cropland, 22.4% grassland, 7.8%
forest/woodland, 5.7% wetland, and 1.0% urban (Luman et al. 1996).
Trapping, handling, and translocation
Swamp rabbits were live-trapped from 9 January–27 February 2004 at
HLCA. Tomahawk collapsible wire live traps (26 cm x 9 cm x 9 cm) were
concentrated in high-use areas, with 30 traps set in a given area. Traps
were placed in brushy areas along runways, or near fresh tracks or fecal
pellets. Traps were covered with burlap to provide greater security for
rabbits and covered with brush where natural understory vegetation was
lacking. Traps were baited with apple and checked daily in the early
morning. Bait was replaced weekly, or as rotting apples were evident.
When capture success was low, traps were relocated every 10–14 days.
All nontarget species were immediately released unharmed and
unmanipulated. Swamp rabbits are most active during cold temperatures
(e.g., < 4.5 oC), whereas capture of nontarget species increases at higher
temperatures. Therefore, the end of trapping in late February was dictated
by rising temperatures.
Handling of captured animals followed Southern Illinois University
Carbondale Animal Use Protocol 03-025. Captured swamp rabbits were
weighed inside the trap to reduce handling time. Weight of individual
Figure 1. Release site (outlined in white) of 2004 swamp rabbit translocation in
Wayne County, IL. The inset highlights Wayne County; and depicts bottomland
hardwood forest as dark gray areas.
2007 A.M. Watland, E.M. Schauber, and A. Woolf 263
swamp rabbits was measured using a spring scale to the nearest 0.10 kg.
Rabbits were removed from traps, placed in capture bags, blindfolded, and
held tightly against the handler’s body to avoid injuries to rabbits due to
struggling. We determined the sex of each rabbit according to the criteria of
Dimmick and Pelton (1996). Each rabbit was marked with a tag in each ear,
and a tissue sample was taken by way of an ear punch from one ear. Captured
rabbits were then fitted with radio transmitters with mortality sensors for
monitoring survival and movements. After being processed, rabbits were
placed in large wooden box traps for transportation. Box traps were lined
with a thick bed of grass, and openings were covered with burlap to ensure
that the rabbits remained as calm as possible during transport.
For many species, temporarily holding translocated animals in captivity
to allow the animals to gain familiarity with and reduce dispersal away from
the release site (i.e., soft release) has increased initial survival relative to
animals that were released immediately (i.e., hard release; Scott and Carpenter
1987). However, the benefits of soft release appear to be ambiguous for
translocated lagomorphs. Survival of translocated Lower Florida Keys
marsh rabbits was relatively high, despite hard release (Faulhaber 2003).
Calvete et al. (1997) found that a soft release increased survival of translocated
European rabbits by 40%, but this improvement resulted from
identification and removal of diseased rabbits prior to release, rather than
improved survival of healthy animals after release. Also, Letty et al. (2000)
found that soft release provided only a small and very temporary (1-day)
improvement in survival of translocated European rabbits. Finally, we did
not know whether the stress of holding swamp rabbits in captivity would
lead to increased mortality. Therefore, we elected to use hard release, and
freed swamp rabbits at the release site within 24 hrs of capture. We specifically
chose a release site in an area of dense cover without abundant predator
sign, to reduce vulnerability to predators.
We monitored swamp rabbit mortality via daylight radiotelemetry. Survival
of each collared rabbit was checked at least every other day for the 2–3
week critical period after release (Calvete et al. 1997), with daily checks
when maximum temperatures were > 4.5 oC until 27 February, to avoid
accelerated carcass decomposition. After 27 February, monitoring was reduced
to once per week, and continued weekly until 31 April 2004.
Biweekly monitoring began in May, and continued until 15 June 2004.
When a mortality signal was detected and the collar was located, the mortality
site and carcasses were photographed and field evidence (presence of
tracks, fur, burial mounds, etc.) was noted. Carcasses were then transported
in a cooler and necropsied to determine causes of mortality.
Eighteen swamp rabbits (9 M, 8 F, 1 escaped) were captured at HLCA in
2067 trap nights, with one rabbit that was captured twice (1 capture per 115
264 Southeastern Naturalist Vol. 6, No. 2
trap-nights). The recaptured rabbit was a male that was tagged and released at
the trap location when first captured, to avoid translocating a highly skewed
sex ratio at that time. However, he was translocated upon recapture at a later
date. Therefore, 9 male and 8 female swamp rabbits were collared and
translocated to the release site. The mean weight of captured swamp rabbits
was 1.92 kg. Thirty-five nontarget animals were also captured, consisting of
27 Procyon lotor Linnaeus (raccoons), 7 Didelphis virginiana Kerr (opossums),
and 1 Sciurus carolinensis Gmelin (gray squirrel).
Rabbits were translocated and released between 14 January and 15 February
2004. Of the 17 swamp rabbits translocated, 14 died by 12 March
2004, and the remaining 3 were alive as of 15 June 2004, when monitoring
was discontinued (Table 1). Eight out of 17 (47%) died within 7 days after
release. A plot of the log-transformed number surviving versus time since
release was decelerating, showing a decline in daily mortality rates as time
passed since release (Fig. 2). Ten swamp rabbits were killed by predators.
Based on the presence of tracks, scat, fur, burial mounds, and the condition
of carcasses, six rabbits appeared to have been killed by mammalian predators,
including coyotes, domestic dogs, and bobcats. Three rabbits appeared
to have been killed by avian predators, based on a lack of other sign and
condition of carcasses. One swamp rabbit was confirmed by a landowner to
have been killed by a domestic dog. Another rabbit was found dead with the
collar lodged inside the mouth. Three rabbits were killed by unknown
Table 1. Characteristics and fates of swamp rabbits translocated from Horseshoe
Lake Conservation Area to a release site in Wayne County, IL, 2004.
ID Sex (kg) Capture date Mortality date Mortality cause
01 M 2.0 14 January 14 February Predation—likely mammalian
02 M 1.9 14 January 30 January Predation—likely mammalian
03 F 2.2 16 January 7 February Collar lodged in mouth
04 F 1.6 16 January -A -
05 M 1.9 16 January 23 January Unknown
06 M 1.9 19 January 1 February Predation—likely mammalian
07 M 2.1 19 January -A -
08 F 2.0 19 January 23 January Domestic dog
09 M 1.7 19 January 26 January Unknown
10 F 2.0 26 January 1 February Predation—likely avian
11 M 2.1 28 January 1 February Predation—likely avian
12 M 1.9 08 February 11 February Predation—likely avian
13 F 2.2 09 February 11 February Predation—likely mammalian
14 F 1.9 12 February -A -
15 F 1.6 12 February 18 February Predation—likely mammalian
16 M 1.9 13 February 24 February Unknown
17 F 1.8 14 February 12 March Predation—likely mammalian
AAlive as of 15 June, 2004.
2007 A.M. Watland, E.M. Schauber, and A. Woolf 265
causes. Carcasses that were retrieved were often in several pieces, or missing
body parts. In general, rabbit carcasses had food in their stomachs and
showed no signs of myopathy. However, only one rabbit carcass had substantial
fat around the kidneys. Of the two intact rabbit carcasses we
retrieved, carcasses mass was ca. 12% less than their mass at capture (1.5 kg
carcass vs. 1.7 kg at capture; 1.75 kg carcass vs. 2.0 kg at capture).
Swamp rabbit habitat in southern Illinois is highly fragmented, and there
are large areas of potentially suitable habitat that are currently unoccupied by
swamp rabbits. Therefore, translocation may provide a means to increase
connectivity among existing populations and promote colonization of uninhabited
patches. However, our results raise some concerns about the potential for
using translocation as a restoration strategy for swamp rabbits in southern
Illinois. The two main issues we encountered were difficulty of capturing large
numbers of swamp rabbits to translocate and high levels of predation on newly
Figure 2. (A) Number alive
(Nt; logarithmic scale) and
(B) instantaneous daily mortality
rate (mt) of swamp rabbits
translocated to Wayne
County, IL, 2004, at varying
days after release (t). Instantaneous
mortality rates were
calculated as: ln(Nt/Nt+Dt)/Dt.
In each panel, the dashed line
represents the expected number
alive or daily mortality
rate given the following relationship,
fitted by maximum
likelihood: mt = 0.090e-0.054t.
266 Southeastern Naturalist Vol. 6, No. 2
Although several studies have presented methods for capturing swamp
rabbits, few have reported high capture success, and even fewer present
handling methods. Although some studies report catching swamp rabbits in
nets, by hand, or with dogs (Conaway et al. 1960, Massengill and Smith
1989), most researchers have used variations of wooden or wire box traps
(Kjolhaug and Woolf 1988, Lowe 1958, Martinson et al. 1961, Massengill
and Smith 1989, Terrel 1972, Toll et al. 1960, Woolf and Barbour 2002). In
previous studies, capture success has been limited, even in sites with high
abundance (Woolf and Barbour 2002). In general, trapping for swamp rabbits
in southern Illinois has only had high success rate during the coldest
months, January–February (Kjolhaug 1986, Kjolhaug and Woolf 1988,
Woolf and Barbour 2002). Kjolhaug (1986) captured a swamp rabbit in
November 1984, but Woolf and Barbour (2002) were unsuccessful trapping
in November–December and after 10 March. The highest capture success in
southern Illinois reported previously was on Bumgard Island from 20 January–
7 February 2000, when 13 rabbits were captured in 471 trap-nights (1/36
trap-nights) (Woolf and Barbour 2002). We had similar results, with the
greatest capture success occurring from 14 January–28 February 2004, when
11 were captured at HLCA in 344 trap-nights (1/31 trap-nights). Thus, there
is a narrow mid-winter window for high success rates in live-trapping for
swamp rabbits in southern Illinois. We were limited by the availability of
traps (n = 60) and personnel (n = 3). A higher level of trapping effort during
this success window would likely have increased the number of rabbits we
could translocate. Failure of mammal reintroductions decreased from 42% to
12% when initial populations were supplemented by additional releases
(Fischer and Lindenmayer 2000).
High initial mortality
Translocated rabbits experienced initial high mortality rates in our study,
with 8 out of 17 (47%) dying within 7 days after release. Some other studies of
translocated lagomorphs have also documented high initial mortality rates
(Calvete and Estrada 2004, Calvete et al. 1997, Letty et al. 2005) but others
have not (Faulhaber 2003, L. P. Hamilton. Seep. 2 pers. comm.). Two main
hypotheses to explain these results are capture-related harm to the animals and
high vulnerability to predators in novel environments. Our trapping methods
were designed to minimize stress and injury to the animals, and field evidence
suggests that capture-related factors were probably not major mortality
causes. We found that most swamp rabbits were relatively calm and easy to
handle, and blindfolding captured rabbits significantly reduced struggling.
Capture myopathy was not evident in any of the necropsies. With the exception
of the single collar-related death, no deaths occurred as a direct result of
being trapped, handled, or transported. Upon finding the rabbit carcass with
the collar lodged in its mouth, we revised our protocol to ensure that subsequently
deployed radio collars were not too loose. Poor condition prior to
release may also contribute to low survival (Swanson 2002). Subcutaneous fat
2007 A.M. Watland, E.M. Schauber, and A. Woolf 267
was lacking in several rabbit carcasses necropsied just a short time following
release, and the rabbits appeared to lose mass after release. This could suggest
that rabbits were in poor condition initially or had trouble finding food after
release. However, the stomachs of all necropsied rabbits contained food, so
they were finding food in the new environment.
Predation was the most important cause of swamp rabbit mortality in our
study, with 10 of 14 (71.4%) deaths of translocated rabbits due to predation.
Other studies have documented high mortality in reintroduced lagomorphs
caused by predators (Massengill and Smith 1989, Swanson 2002). Predation
is a major cause of mortality in studies of natural populations, as well. In
Kjolhaug’s (1986) study, predation accounted for 15 of 18 (83%) documented
deaths. Of 19 swamp rabbits monitored in 2000, 15 suffered predation
(Woolf and Barbour 2002).
Improvements in release design and increased management efforts may
increase the effectiveness of translocations (Fischer and Lindenmayer 2000,
Griffith et al. 1989, Wolf et al. 1996). For example, Calvete and Estrada
(2004) found that dense cover, culling predators, and electric fencing to
exclude predators increased the survival of translocated European rabbits. We
intentionally released swamp rabbits in dense cover, but did not actively
manage predators. Predator abundance in intended release sites should be
studied, and control options considered. Predator control methods could
be used in areas that experience high losses due to locally intense predation
(Swanson 2002). Removing the major source of mortality in animal reintroductions
can increase success (Fischer and Lindenmayer 2000). However,
these methods are often resource-intensive and controversial. Efforts may be
better focused on ensuring the presence of adequate understory cover, because
this is probably most critical for translocated lagomorphs where predation
rates are high (Swanson 2002). In addition, the choice of a hard vs. soft release
may affect the success of translocation. We employed a hard release approach,
which involves simply releasing the animal into its new environment as
opposed to a soft release, which involves keeping the animal captive in the
new environment for a period of adjustment (Scott and Carpenter 1987).
However, Letty et al. (2000, 2005) found high initial mortality among translocated
European rabbits, despite soft release techniques. Calvete and Estrada
(2004) found that predator control had a much larger effect on survival of
translocated European rabbits than the choice of hard versus soft release.
In the long term, persistence of swamp rabbits in Illinois will likely benefit
more from efforts to increase the area and connectivity of habitat patches than
from active translocation. Although viable swamp rabbit populations exist on
public lands, restoration of populations or habitat will require cooperation of
private landowners. At the time of this study, there were >128,000 ha
of bottomland hardwood forests remaining on private lands in Illinois
(A.M.Watland, unpubl. data). Currently, the largest contiguous blocks of
habitat are concentrated along the watersheds of the Big Muddy and
Kaskaskia rivers. However, managing or creating disturbance to allow early
268 Southeastern Naturalist Vol. 6, No. 2
successional growth may be necessary if swamp rabbits are to recolonize to
these areas. High-quality habitat for swamp rabbits consists of early-successional
bottomland hardwood forest and canebrakes within 2 km of permanent
water with adjacent upland refugia where the rabbits retreat during floods
(Allen 1985, Conaway et al. 1960, Kjolhaug 1986, Korte 1975, Terrel 1972,
Zollner et al. 2000). Schmidt et al. (2000) report that the area of saplingseedling-
size stands in Illinois has decreased since 1985, while the percentage
of Illinois timberland consisting of saw-timber size trees increased from 64%
in 1985 to 72% in 1998, indicating a lack of significant disturbance through
natural occurrences or timber harvest (Schmidt et al. 2000). Therefore, publicprivate
partnerships promoting afforestation of marginal agricultural land and
active timber management are likely to have the greatest benefit for swamp
rabbits in Illinois.
Funding for this research was provided through Federal Aid in Wildlife Restoration
Project W-106-R. Fieldwork assistance during live-trapping efforts by C.
Greene, and especially the tireless efforts of C. Bloomquist were greatly appreciated.
We are indebted to J. Cole and D. Woolard of the Illinois Department of Natural
Resources for their particular help in conducting this study, and to J. Thurston for
permission to trap on Horseshoe Lake Conservation Area. MeadWestvaco Corp. also
allowed us to trap on Bumgard Island, although we caught no swamp rabbits there.
We also wish to thank the many landowners who allowed us access to their property
while investigating potential release sites, especially G. Manda, owner of our primary
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