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Sylvilagus palustris

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA LAGOMORPHA LEPORIDAE

Scientific Name: Sylvilagus palustris
Species Authority: (Bachman, 1837)
Common Name(s):
English Marsh Rabbit, Lower Keys Rabbit, Lower Keys Marsh Rabbit, Key Rabbit
Taxonomic Notes: This species is in need of taxonomic evaluation (Chapman and Ceballos 1990). Hall (1981) recognizes two subspecies: Sylvilagus palustris paludicola and S. p. palustris (Hall 1981). Hoffmann and Smith (2005) include S. p. hefneri in addition to the two subspecies listed by Hall (1981).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Faulhaber, C.A. & Smith, A.T.
Reviewer(s): Boyer, A.F. & Johnston, C.H. (Lagomorph Red List Authority)
Justification:
Sylvilagus palustris is a widespread species, known to be abundant in some parts of its range, particularly along the Ogeechee, Satilla, and St. Mary’s Rivers in Georgia (Whitaker and Hamilton 1998). Only the subspecies S. p. hefneri is experiencing severe decline, restricted area of occupancy, severely fragmented populations, and small population size (Faulhaber 2003).

The subspecies S. p. hefneri meets IUCN Red List Criteria B1ab(ii) and B2ab(ii) for Critically Endangered. First, based on surveys conducted from 2001-2004 by C.A. Faulhaber and N. Perry of Texas A&M University (2003), the subspecies' extent of occurrence is 90 km², and the area of occupancy is less than 10 km². Faulhaber (2003) mapped 523 ha of occupied habitat and 278 ha of potential habitat in the rabbit's range, with no key containing more than 290 ha of suitable habitat. Also, S. p. hefneri populations are "severely fragmented." S. p. hefneri has been known to disperse as far as 2 km (Forys and Humphrey 1996), so most patches within keys are likely part of the same "subpopulation." All of these subpopulations are relatively small (less than 250 mature adults) and isolated from one another. Finally, the area of occupancy has declined over the past 10 years. A distribution survey conducted between 2001 and 2003 found a net loss of nine of the 76 patches identified in surveys conducted from 1988-1996 (Faulhaber 2003). Because the rabbit occurs as a metapopulation, local extinctions and recolonization are expected to occur (Forys 1995, Forys and Humphrey 1996, Faulhaber 2003). However, most of the recently extirpated patches are unlikely to be recolonized due to habitat fragmentation and isolation (Faulhaber 2003).

Geographic Range [top]

Range Description: Sylvilagus palustris occurs in the south-eastern coastal lowlands of the United States from the Dismal Swamp of southeastern Virginia, through eastern North Carolina, southeastern South Carolina, southern Georgia, southern Alabama, and most of Florida, excluding the extreme southeast, but including the Lower Keys of Florida (Chapman and Willner 1981; Chapman and Ceballos 1990).

S. p. hefneri:

S. p. hefneri is restricted to the Upper and Lower Keys of Florida (Chapman and Ceballos 1990). Historically, the subspecies probably occupied all keys with suitable habitat in the Lower Keys. Currently, S. p. hefneri can be found on only 4 of the larger keys (Boca Chica, Saddlebunch, Sugarloaf, and Big Pine Keys) and on some of the surrounding smaller keys. More than 50% of the total occupied habitat was found on Big Pine and Boca Chica keys during a 2001-2005 survey (Faulhaber et al. 2007). This survey also concluded a net loss of occupied patches compared to a conglomerate of surveys conducted between 1988-1995 (see discussion for possible cause) (Faulhaber et al. 2007). The greatest loss of occupancy occurred on Saddlebunch Keys (Faulhaber et al. 2007). There is a gap in the rabbit's current distribution between Big Pine Key and Sugarloaf Key, and the rabbit has been extirpated on Key West (Faulhaber 2003). A recent phylogenetic analysis determined that populations on either side of the gap island complex (islands extending from Middle Torch Key to Cudjoe Key) represent distinct haplogroups with little gene flow between the two (Crouse 2005). However, the author notes that an investigation of more individuals from a greater variety of locations east of the gap would elucidate the degree of geographic separation (Crouse 2005). Fecal pellets of S. p. hefneri were discovered in a single patch on No Name Key in 2001 but have not been located on the island since (Faulhaber 2003).

S. p. hefneri exists as a metapopulation in small patches of brackish and freshwater wetland habitat. A distribution survey conducted by Faulhaber (2003) found 535 ha of occupied habitat and 266 ha of potential habitat. However, because the subspecies exists as a metapopulation, the area of occupancy varies through time. These estimates are conservative, as they only included areas of known use (e.g. areas with fecal pellets or sightings of individuals). It is possible that these estimates underestimate the area of occupancy, because the degree of use of adjacent, "unsuitable" vegetation types (e.g. upland hardwood hammocks, pinelands, and mangrove swamps) could not be determined. The greatest abundance of the subspecies occurs on Boca Chica, Saddlebunch, Sugarloaf, and Big Pine Keys.

The current extent of occurrence for the subspecies S. p. hefneri is 90 km² (Faulhaber 2003).
Countries:
Native:
United States (Alabama, Florida, Georgia, North Carolina, South Carolina, Virginia)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Other than the Lower Keys subspecies, little is known about the populations of Sylvilagus palustris, but it is known to be locally abundant in favorable habitat, with the largest populations occurring along the Ogeechee, Satilla, and St. Mary’s rivers in Georgia (Whitaker and Hamilton 1998).

S. p. hefneri:

Once common in the Lower Keys, S. p. hefneri is now rare and has become extirpated on several islands within its range. In 1999, the United State Fish and Wildlife Service estimated that only 100-300 adults remained (Faulhaber 2003). A widened search led to the discovery of additional occupied habitat patches from 2001-2003. However, the overall population size remains low. A recent study by Faulhaber (2003) at Texas A&M University estimated that the current population contains 200-700 mature individuals, with no key containing more than 250 mature individuals. A PVA model using data collected from 1991-1993 predicted that the species would have a 100% probability of extinction in 50 years (Forys 1995; Forys and Humphrey 1999).

S. p. hefneri occurs as a metapopulation in small habitat patches on 4 larger keys and several smaller surrounding islands. A distribution survey conducted between 2001-2003 mapped 220 patches of occupied (n=102) and potential (n=118) habitat ranging in size from 0.1-51 ha. The median patch size was 2.4 ha (interquartile range = 0.7-5.1 ha) (Faulhaber 2003). Some of these patches may be part of the same local population; Faulhaber (2003) hypothesized that the occupied patches are arranged into 56 occupied local populations. These local populations interact through dispersing individuals. Dispersal may be frequent enough that these local populations do not fit the IUCN's definition of "subpopulations." Lower Keys marsh rabbits have been known to disperse as far as 2 km (Forys and Humphrey 1996), so most patches within keys are likely part of the same "subpopulation."

However, although the species is thought to be an excellent swimmer (Tomkins 1935), the rate of genetic exchange between keys is unknown (researchers at Texas A&M University were examining this issue at the time of writing). Certainly, rabbits on Big Pine Key and its surrounding islands are isolated from rabbits on Boca Chica, Saddlebunch, and Sugarloaf keys. Moreover, rabbits have not naturally recolonized the keys between Big Pine Key and Sugarloaf Key, indicating that the interchange of dispersers among keys is probably low. The Lower Keys marsh rabbit may therefore be separated into three large subpopulations (Boca Chica Key, Saddlebunch/Sugarloaf complex, and Big Pine Key) and several small subpopulations on outer islands (Faulhaber 2003).
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: Sylvilagus palustris occurs in marshy habitats, mostly with brackish waters, but is also known to occur along freshwater wetlands (Tomkins 1935; Chapman and Ceballos 1990). It has also been documented in grassy fields; mangroves; hammocks; fallow tomato fields; and “rank vegetation” along canals, ditches, roadsides, and cultivated fields (Carr 1939; Schwartz 1952; Layne 1974). It is a nocturnal species that often walks as opposed to hopping and is a good swimmer (Chapman and Ceballos 1990).

Reproduction occurs all year for S. palustris, with around six litters annually per each adult female, with approximately three young per litter (Chapman and Ceballos 1990). Gestation is approximately 39-40 days (Hamilton and Whitaker 1979). The diet of S. palustris includes a variety of aquatic plants, herbaceous material from shrubs, trees, and woody plants, cultivated crops (Chapman and Willner 1981), as well as grasses, sedges, and flowers (Whitaker and Hamilton 1998).


S. p. hefneri:

S. p hefneri is usually found in saltmarsh/buttonwood transition zones and freshwater marshes within the Lower Keys (Forys et al. 1996; Faulhaber 2003). The saltmarsh/buttonwood transition zone forms the transition between lowland mangrove areas and upland hardwood hammocks and pineland. This transition zone can be subdivided into: 1) an intertidal marsh, occurring at lower elevations and characterized by low halophytic vegetation; 2) a grassy saltmarsh, which occurs at slightly higher elevations and is dominated by grasses and Cyperaceae; and 3) buttonwood transitional vegetation, consisting of grasses and Cyperaceae with an open canopy of buttonwood transitional habitat for foraging and daytime resting sites (Forys 1995). Forys (1995) found that the grassy saltmarsh was commonly used for nests. Rabbits also forage in the intertidal marsh and mangroves, and they occasionally use mangroves for daytime form sites (Forys 1995; Faulhaber 2003).

Freshwater wetlands used by S. p. hefneri are usually dominated by sawgrass (Cladium jamaicense) and often include patches of buttonwood trees or other hardwoods (Faulhaber 2003). Faulhaber (2003) noted that rabbits on Boca Chica Key inhabited disturbed mesic grasslands dominated by Schizachyrium gracile, with patches of invasive exotic lead tree (Leucaena leucocephala) used for cover. Historically, S. p. hefneri also was found on coastal beach berms (United States Fish and Wildlife Service 1999).

S. p. hefneri exists as a metapopulation in small patches of habitat spread throughout the Lower Keys (Forys and Humphrey 1996). Adult rabbits establish permanent home ranges within these patches, with same sex ranges rarely overlapping (Forys 1995). The average home range reported by Forys and Humphrey (1996) was 3.96 ha, while data collected by Faulhaber (2003) suggests a mean home range of 1.2 ha . Females reproduce year-round, with a mean of 3.7 litters per year and 1-3 young per litter (Forys 1995). The reproductive rate of the Lower Keys marsh rabbit may be lower than that of other subspecies; Holler and Conaway (1979) noted a mean of 5.7 litters per year with 2-4 young per litter for S. p. paludicola. Young leave the nest after about 2 weeks and often disperse from their natal patch after 8-10 months (Forys 1995). Dispersal appears to be male-biased, and dispersing rabbits tend to use thick cover and native vegetation types rather than disturbed areas (Forys 1995).

Known predators of the S. p. hefneri include raptors, eastern diamondback rattlesnakes (Crotalus adamanteus), and raccoons (Procyon lotor) (Howe 1988; Forys 1995).
Systems: Terrestrial

Threats [top]

Major Threat(s): Sylvilagus palustris is considered an agricultural pest in some areas, especially in sugarcane fields of southern Florida (Whitaker and Hamilton 1998). They are hunted in the southern United States (Whitaker and Hamilton 1998).

S. p. hefneri:

The U.S. Fish and Wildlife Service listed S. p. hefneri as endangered in 1990. The primary reason cited for listing the species was the loss and fragmentation of its habitat due to human development. Over the last 25 years, greater than 50% of the Lower Keys marsh rabbit's habitat was lost to human development. Human development has also resulted in increased isolation for some patches, reducing the likelihood of recolonization. Although the rate of habitat loss has slowed since the rabbit received legal protection, habitat destruction and fragmentation remain significant threats to the species' persistence (Faulhaber 2003). LaFever et al. (2007) modelled the potential impact resulting from oceanic rise, due to thermal expansion only, on S. palustris habitat. They found that the three most important factors impacting potential change were: the rate at which sea-level rise impacts the ability of flora migration upslope, the magnitude in terms of the overall oceanic rise and whether it is great enough to reach S. palustris habitat, and whether or not humans abandon low-lying habitat, where abandonment would facilitate greater ease of upslope migration by vegetation. They concluded that non-static strategies needed to be implemented regarding management of the local ecosystem (i.e. consideration of land-use planning, use of bioclimatic reserve systems in conjunction with corridors) (LaFever et al. 2007).


Additional threats to the subspecies include mortality from cars and cats, both domestic and feral. Cars and cats accounted for more than half of the mortalities observed by E.A. Forys on Boca Chica in the early 1990s (Forys 1993). Faulhaber (2003) estimated that just over half of occupied local populations are reasonably likely to have current or future impacts due to cats. A recent population viability analysis supports this assertion, indicating that without predator control, habitat improvement efforts may result in a negligible increase in the chance for persistence (LaFever 2006). The subspecies is also threatened by habitat degradation from invasive exotic plants, trash dumping, mowing and off-road vehicle use (Forys 1993). If left unchecked, invasive exotic vegetation can render patches unsuitable for rabbits. Management efforts have reduced the threat of invasive exotic vegetation on some government-owned properties, but invasive exotic vegetation remains a problem on privately-owned land parcels and even on some government properties. Currently, trash dumping and off-road vehicle use appear to be less of a problem than in the past (Forys 1993; Faulhaber 2003).

It has been suggested that invasive exotic fire ants (Solenopsis invicta) and elevated raccoon (Procyon lotor) densities also pose a threat to the subspecies, but this has not been confirmed (Forys 1993). Historically, poaching may have contributed to the rabbit's decline, but poaching does not appear to be a major threat at the current time. Feral hogs degraded habitat and may have caused the extirpation of rabbits on Little Pine Key, but hogs were removed from the islands in the 1990s (Wilmers 2003).

Conservation Actions [top]

Conservation Actions: S. p. hefneri:

Policy-based Actions: S. p. hefneri was listed as an endangered species by the United States Fish and Wildlife Service in 1990. The United States Fish and Wildlife Service (1999) has developed and is in the process of implementing a recovery plan for the subspecies. Although feral and domestic cats are known threats to the subspecies, control measures have yet to be implemented, except on United States Navy land.

Research Actions: The distribution of the subspecies was recently updated (Faulhaber 2003) but the current population size has not been estimated. The ecology of the Lower Keys marsh rabbit is fairly well known (Forys and Humphrey 1996), though further research is needed concerning nighttime habitat use and nestling/juvenile mortality (Faulhaber 2003). Further research should also examine the movements, habitat use, and impact of feral and domestic cats throughout the rabbit's range. A population viability analysis model was developed for the subspecies (Forys and Humphrey 1999). Current distribution data need to be added to the model, and additional demography data would improve the model's predictive capability.

Habitat-based actions: Approximately two-thirds of local populations occur entirely on publicly-owned and military land (Faulhaber 2003). Faulhaber (2003) estimated that nearly 500 ha of privately-owned land could be purchased to ensure the protection of existing occupied and potential habitat patches and the area immediately surrounding these patches. Further land acquisition would help protect connectivity between local populations. Efforts to control invasive exotic vegetation are ongoing in rabbit habitat under public and military ownership. Future research and management should involve restoring rabbit habitat and enhancing cover in existing habitat (Faulhaber 2003).

Species-based Actions: A pilot reintroduction program has recently been initiated for the subspecies (Faulhaber 2003). If current efforts prove successful, the reintroduction program could be expanded in the future, possibly in conjunction with in situ captive propagation (Faulhaber 2003). Translocation of wild-caught marsh rabbits had a 100% and a 81% survival rate for the individuals released on Water Key and Little Pine Key, respectively. This study showed that translocation of a small founder group can be successful, important when working with a species, like S. palustris, whose source group could be imperiled by the removal of too many individuals (Faulhaber et al. 2006).

Citation: Faulhaber, C.A. & Smith, A.T. 2008. Sylvilagus palustris. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 18 September 2014.
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