Notes on nesting and litter size of wild swamp rabbits (Sylvilagus aquaticus) in Louisiana. (Short Communication).
Key words: Sylvilagus aquaticus, swamp rabbit, reproduction, nests, litter size.
The swamp rabbit (Sylvilagus aquaticus Bachman) occurs in 14 states of the Gulf Coastal Plain and lower Mississippi Valley, with a range extending from the Gulf of Mexico north to Illinois and Indiana, westward to eastern Texas, Oklahoma, and Kansas, and east to Georgia and South Carolina (Chapman and Feldhamer 1981). Despite this extensive distribution, S. aquaticus remains one of the least studied North American lagomorphs (Chapman and Feldhamer 1981, Zollner et al. 2000). Because swamp rabbit nests are well camouflaged and difficult for investigators to locate (Mumford and Whitaker 1982), there is a notable paucity of data on nest construction and litter size among wild populations (Sorensen et al. 1972). Indeed, data on most aspects of reproduction are derived from studies of captive animals (Holler et al. 1963; Sorensen et al. 1968, 1972), and only five reports of nesting by wild swamp rabbits are available (Strecker and Williams 1929, Svihla 1929, Goodpaster and Hoffmeister 1952, Lowe 1958, Hunt 1959). Furthermore, while swamp rabbits are abundant throughout Louisiana (Lowery 1974) there are only two accounts of nesting and litter size from the state (Svihla 1929, Hastings 1954). We herein report descriptions of additional nests and data on litter size from wild swamp rabbits in southeastern Louisiana.
Our observations of swamp rabbit nesting were made opportunistically in East Baton Rouge and Ascension Parishes, Louisiana from 1984 to 2000. The length and width of each nest was measured at ground level. If the nest was constructed in an excavation, depth was measured from the bottom of the excavation to ground level. Note was made of general nest structure, nest materials, vegetation at the nest site, and surrounding habitat; any neonates present in the nest were counted. Nests found in 2000 were photographed and vouchers deposited in the Campbell Museum (CUSC), Clemson University, Clemson, South Carolina. Mean values are presented as [+ or -] SD.
RESULTS AND DISCUSSION
We examined six swamp rabbit nests in southeastern Louisiana (Table 1). Nests were oblong structures composed of loosely woven dried vegetation, lined with rabbit fur, and had a single entrance (Fig. 1); a description consistent with reports from both wild (Strecker and Willaims 1929, Svihla 1929, Goodpaster and Hoffmeister 1952, Lowe 1958, Hunt 1959) and captive (Holler et al. 1963, Sorensen et al. 1972) swamp rabbits. Nests averaged 19.3 [+ or -] 1.7 cm long and 17.0 [+ or -] 2.1 cm wide. Dimensions of wild swamp rabbit nests have rarely been reported; one measured "about six inches [15.2 cm] in diameter" (Hunt 1959), and another was "6.5 inches [16.5 cm] wide" (Lowe 1958). The mean diameter of 11 nests in a captive population was 15.5 cm (Holler et al. 1963).
[FIGURE 1 OMITTED]
The vegetation used for nest construction probably reflects the availability of materials near the nest site. Two nests we found in forested habitats were composed of dried hardwood leaves while the others consisted principally of dried grass. Svihla (1929) reports a nest composed of Spanish moss (Tillandsia usneonides). In captivity, only nests with neonates were fur-lined; "dummy nests" containing no young were unlined (Holler et al. 1963, Sorensen et al. 1972). Ecke (1955) suggests the fur lining functions as insulation.
Four (67%) nests we examined were constructed in shallow excavations with a mean depth of 6.5 [+ or -] 2.6 cm. Among accounts of wild swamp rabbit nesting only Lowe (1958) reports a similar excavation, "approximately 3 inches [7.6 cm] deep". Others describe nests as entirely aboveground (Svihla 1929, Goodpaster and Hoffmeister 1952) or fail to specify whether or not an excavation was present (Strecker and Williams 1929, Hunt 1959). However, Holler et al. (1963) and Sorensen et al. (1972) found 100% (N=11) and 93.6% (N=47) respectively, of nests constructed by captive swamp rabbits were built in shallow excavations.
Sorensen et al. (1972) found that captive S. aquaticus positioned 61.7% (N=47) of their nests under or against natural or man-made objects such as boards, logs, fences, utility poles, and trees, but note that the frequency of this behavior in the wild is poorly documented. Four (67%) nests we examined and three of five (60%) wild nests described in the literature (Strecker and Williams 1929, Svihla 1929, Hunt 1959) were constructed under or against similar structures. Positioning nests under or against such objects probably enhances concealment (Sorensen et al. 1972).
Our data and previous reports indicate swamp rabbits nest in a variety of habitats. We found nests in bottomland hardwood (Quercus spp., Celtis laevagata, Liquidambar styraciflua, Taxodium distichum) and old-growth beech (Fagus grandiflora)--magnolia (Magnolia grandiflora) forests, old-field vegetation, and improved pasture. Other nests have been found "near the edge of a wooded area" (Svihla 1929), in a powerline right-of-way (Lowe 1958), and among a "heavy weed patch" (Goodpaster and Hoffmeister 1952). Svihla (1929) found old nests in coastal marshland following grass fires, and Lowe (1958) received second-hand reports of nests in "bottomland hay fields". Our observations of nesting along an interstate highway right-of-way and amidst an ornamental plant nursery indicate swamp rabbits will nest in close proximity to human activity.
Living neonates were present in four nests we examined. Direct counts were possible at two nests; litter size at a third nest was determined by dissecting a cottonmouth (Agkistrodon piscivorus) found consuming neonates (Platt and Rainwater 2000). At least two young were observed to flee from another nest accidentally uncovered by workmen at an ornamental plant nursery, but because others may have escaped unnoticed, these were not included in our calculation of mean litter size. Litter size could not be determined at the remaining two nests. Pooling our data with Svihla (1929) who reported litters of six and three, we calculated a mean litter size of 3.4 [+ or -] 1.5 (range=2 to 6; N=5) for S. aquaticus in Louisiana. Mean litter size based on embryo counts of wild S. aquaticus in Louisiana range from 2.84 (SD not reported; N=43; Hastings 1954) to 3.7 (SD not reported; sample size unclear, N= 107; Svihla 1929). The litter of six found by Svihla (1929) remains the largest yet reported for wild S. aquaticus. Sorensen et al. (1968) noted a single litter of six among 38 litters produced by captive females.
We found swamp rabbit nests and neonates only during March (4) and April (2) in south Louisiana. Reproduction among S. aquaticus probably occurs year-round in the southern parts of its range (Chapman and Feldhamer 1981). Gravid females have been collected from January through September in south Louisiana (Svihla 1929, Hastings 1954). Similarly, Hunt (1959) found gravid females in southern Texas during every month except September, October, and December, but added that females killed during these months exhibited flaccid uteri suggestive of recent (<10 days) pregnancy.
TABLE 1. Dimensions, litter size, and description of swamp rabbit (Sylvilagus aquaticus) nests found in East Baton Rouge and Ascension Parishes, Louisiana from 1984 to 2000. NAG=Nest constructed aboveground, no excavation present. Nest dimensions (cm) Litter Date Length Width Depth size 26 March 1984 19 14 NAG 3 15 March 1991 21 17 10 3 15 March 1991 20 20 NAG 2 29 March 2000 20 18 5 2? 7 April 2000 16 18 4 ? 29 April 2000 20 15 7 ? Date Habitat/nest description/notes 26 March 1984 Bottomland hardwood forest; Rubus thicket along creek bank; site sub- ject to flooding; Agkistrodon piscivo- rus consuming litter. 15 March 1991 Old-growth beech-magnolia forest; nest in excavation beneath decayed log (diameter ca. 30 cm); dense ground cover of Lonicera japonica. 15 March 1991 Interstate highway right-of-way; nest in grass clump at base of Platanus occidentalis (DBH = 11.3 cm). 29 March 2000 Ornamental tree nursery ca. 10 m from old-field dominated by Rubus, Solidago, and Ambrosia trifida; nest in excavation at base of Ambrosia trifida; (CUSC 3061). 7 April 2000 Improved pasture (Paspalum, Loloium, and Trifolium) used for livestock grazing; nest 30 m from forest cov- er; exposed by mowing; remains of neonate in nest; (CUSC 3058). 29 April 2000 Old-field dominated by Sapiuim sebi- ferum with understory of Rubus and Rosa; nest in excavation at base of Rosa clump; 4 m from forest edge and 10 m from road; exposed by predators; remains of neonate nearby; (CUSC 3059).
Mike Leggio is thanked for generous field assistance over the years and Stanlee Miller for archiving material in the Campbell Museum. Stephen Johnson (Wildlife Conservation Society) and librarians at Texas Tech University provided references. Harry Callahan commented on an earlier draft of this manuscript. Phil Witter kindly allowed access to his property. Support for SGP was provided by Wildlife Conservation Society. TRR was supported by the ARCS Foundation, Inc., Lubbock, Texas.
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Steven G. Platt Wildlife Conservation Society P.O. Box 1620 Phnom Penh Cambodia Thomas R. Rainwater The Institute of Environmental and Human Health Department of Environmental Toxicology Texas Tech University Box 41163 Lubbock, TX 79409-1163
Thomas R. Rainwater, Corresponding author (Email: email@example.com).
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|Author:||Platt, Steven G.; Rainwater, Thomas R.|
|Publication:||The Proceedings of the Louisiana Academy of Sciences|
|Date:||Jan 1, 2001|
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