DIET OF THE CANEBRAKE RATTLESNAKE (CROTALUS HORRID US A TRICA UDA TUS): AN ADDITIONAL RECORD AND REVIEW.
Abstract.--In June 1993, a radio-tagged bobwhite quail (colinus virginianus and a cotton rat (Sigmodon hispidus) were recovered from the stomach of an adult canebrake rattlesnake (Crotalus horridus atricaudatus) in South Carolina. These data and a review of the literature indicate C. horridus atricaudatus is a generalist predator that opportunistically consumes a wide variety of prey. The diet consists primarily of mammals; rodents and rabbits are the most frequently reported prey. Birds and reptiles constitute a relatively minor portion of the diet. Bobwhite quail are the most frequently reported avian prey. There is no evidence for ontogenetic variation in the diet, due to the failure of previous workers to report snake size in relation to prey size.
Two subspecies of Crotalus horridus Linnaeus are currently recognized: the timber rattlesnake, C. horridus horridus Linnaeus and the canebrake rattlesnake, C. horridus atricaudatus Latreille (Tennant & Bartlett 2000). The canebrake rattlesnake inhabits lowlands from southwestern Virginia, along the Atlantic Coastal Plain to northern Florida, westward to central Texas, and northward in the Mississippi Valley to southern Illinois (Ernst 1992). Populations in many regions have declined due to habitat destruction, road mortality and direct human persecution (Mitchell 1994; Rudolph & Burgdorf 1997). The ecology of C. horridus atricaudatus remains poorly known (Brown 1993). In particular, scant attention has been devoted to dietary studies, and the few available data are located in widely scattered and often obscure sources. This report provides an additional observation and summarizes the existing information on the food habits of C. horridus atricaudatus.
METHODS AND STUDY SITE
On 28 June 1993, a female bobwhite quail (Colinus virginianus) and a cotton rat (Sigmodon hispidus) were recovered from an adult canebrake rattlesnake (TL = 129 cm). The quail (mass = 157 g) was originally trapped on 18 March 1993 and equipped with a radio transmitter as part of a three-year study on the response of quail populations to habitat modifications resulting from herbicide treatment (Hawkes 1995). This work was conducted on a 400 ha loblolly pine (Pinus taeda) plantation approximately 11 km southwest of Allendale, Allendale County, South Carolina. The study site was clearcut and burned in 1991, and loblolly pine seedlings were planted in 1992. Dominant vegetation included loblolly pine, broom sedge (Andropogon sp.), lespedeza (Lespedeza bicolor), blackberry (Rubus sp.) and numerous hardwood seedlings and sprouts including oak (Quercus sp.), sweetgum (Liquidambar straciflua and sumac (Rims sp.).
RESULTS AND DISCUSSION
The radio-tagged quail was located periodically during April, May and June 1993. On 4 June the quail was found incubating a clutch of 13 eggs, and then apparently abandoned the nest on 11 June. While attempting to relocate the quail on 28 June, the bird's transmitter signal was found emanating from a rattlesnake coiled in a dense Rubus sp. thicket. The snake was collected, immediately dissected, and the two prey items removed. The cotton rat (TL including tail ca. 14 cm) was undigested. Digestion of the quail was nearly complete; only a compact mass of feathers, an aluminum leg band, bone fragments and the transmitter remained. A voucher photograph of the rattlesnake (CUSC 1702) was deposited in the Campbell Museum, Clemson University, Clemson, South Carolina.
The quail was probably consumed between 11 (last day hen was found on nest) and 16 (first day hen was found absent from nest) June. The bird was not monitored during the interim, but from 16 June onward there was a notable decrease in the strength of the telemetry signal (presumably because the transmitter was in the digestive tract of the snake). At this point the quail was believed to be alive as telemetry exercises placed the bird at slightly varying positions during successive monitoring periods. In hindsight, it is likely that snake movements were being tracked rather than those of a living quail. All radio--locations after 16 June were within 50 m of where the snake was collected, approximately 85 m from the quail nest, and within the foraging area of the hen. It could not be determined if the hen was captured while incubating or foraging. Reinert et al. (1984) describe the predatory behavior of C. horridus as "sit-and-wait." Assuming C. horridus atricaudatus utilizes a similar foraging strategy, it is likely the bird was taken while moving rather than sitting on the nest. Additionally, observations on 16 June indicate no evidence of disturbance at the nest site.
A review of the literature reveals records for an additional 82 canebrake rattlesnakes and 90 prey items (Table 1). Subspecific identification of rattlesnakes was given in most accounts; however, when this was not reported it was assumed only C. horridus from coastal plain and sandhill regions were C. horridus atricaudatus (cf. Ernst 1992). Authors identified individual prey items from the analyses of stomach contents (n = 84) and feces (n = 1), or by direct observation of feeding (n = 5). Accounts consisted primarily of anecdotal lists of prey species, and information on prey size was rarely reported. Therefore, frequency of occurrence (%) was used to assess the relative importance of each prey species (Hyslop 1980).
The diet of C. horridus atricaudatus consists largely of mammals (80.4%). Rodents (not including tree squirrels, Sciurus sp.) and rabbits (Sylvilagus sp.) are the most frequently reported prey and together constituted 62.0% of all occurrences. Sigmodon hispidus is the most frequently reported small rodent. Allen & Neill (1950) also list wood rats (Neotorna floridana), "barn rats" (Rattus sp.), white-footed mice (Peromyscus sp.) and pocket gophers (Geomys pinetis) among stomach contents, but these unquantified occurrences are not included in Table 1. According to Reinert et al. (1984), C. horridus is an opportunistic predator consuming small terrestrial rodents in proportion to their abundance. Tree squirrels are taken infrequently by C. horridus atricaudatus, and are probably exposed to rattlesnake predation only when foraging terrestrially. A raccoon (Procyon lotor) is the largest mammalian prey item reported (Martin & Wood 1955).
Birds comprise a relatively minor portion of the diet (13.0%), and the bobwhite quail is the most frequently consumed species. Quail typically walk, rather than fly, between foraging, nesting and roosting sites (Rosene 1969), and this behavior may render them more susceptible to predation by C. horridus atricaudatus. Keeps (1882) also reported "several quail" in a canebrake rattlesnake, but this unquantified observation was not included in the present analysis. Additionally, Allen & Neill (1950) found "small birds" and "field sparrows" (Spizella pusilla?) among stomach contents, but likewise failed to quantify their observations. A clapper rail (Rallus longirostris) is the largest avian prey item reported (Grant 1970).
Reptiles are the least frequently reported prey (6.5%). The only quantified observations are those of Hamilton & Pollack (1955), who recorded three species of terrestrial lizards from C. horridus atricaudatus collected at a single site in Georgia. Allen & Neill (1950) state that "lizards" occurred among the stomach contents of juveniles, but provide no further information. According to Tennant (1998), Sceloporus undulatus are readily accepted by captive C. horridus atricaudatus. Juveniles of some North American crotalids reportedly consume snakes (Mushinsky 1987), but there is little evidence for ophiophagy among C. horridus atricaudatus. Wright & Wright (1957) note that small snakes are consumed, but provide no corroboration. Some general accounts (Klauber 1956; Wright & Wright 1957) include insects and anurans in the diet, but no substantiated reports were found.
Evidence that mature snakes consume a different array of prey species than younger conspecifics is widespread, and especially evident in larger species (Mushinsky 1987). In general, the trend is the larger the snake, the larger the individual prey item that can be manipulated and swallowed (Mushinsky 1987). According to Allen & Neill (1950) juvenile C. horridus atricaudatus consume ectothermic prey and small rodents, while the adult diet consists principally of larger rodents. However, the basis for their conclusion is not stated. Additional empirical evidence for ontogenetic variation in the diet is lacking, and accounts rarely include data on snake size in relation to prey size. Because male C. horridus atricaudatus attain a larger body size than females (Gibbons 1972), sexual differences in prey consumption may also exist. It is significant to note that the largest reported prey item was consumed by a large (TL = 182 cm) male rattlesnake (Martin & Wood 1955).
In summary, the available data indicate C. horridus atricaudatus is a generalist predator that opportunistically consumes a variety of endothermic and ectothermic prey. Based on frequency of occurrence, small to medium-sized terrestrial mammals are the most important prey, while birds and reptiles constitute a relatively minor portion of the diet. The paucity of data on snake size in relation to prey size precludes testing hypotheses regarding ontogenetic patterns of prey consumption. Future research should address these questions.
Steven Johnson (Wildlife Conservation Society) and the interlibrary loan staff at Texas Tech University are thanked for obtaining several obscure references. Additional references were provided by Thaddeus Axlerod and Lance Fontenot. Whit Gibbons is thanked for sharing his knowledge of canebrake rattlesnakes in South Carolina. Ronald J. Kendall provided research guidance on bobwhite habitat evaluation, a project jointly funded by the American Cyanamid Company and the Westvaco Corporation. Blame Williamson's assistance with field operations is greatly appreciated.
* Current address:
The Institute of Environmental and Human Health
Texas Tech University, Box 41163
Lubbock, Texas 79409-1 163
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Table 1. The number (n) and frequency of occurrence (%) of prey items (n=92) identified from canebrake rattlesnake (n=83) stomach contents, feces or feeding observations. Prey item n % MAMMALIA Mammals (unidentified) 5 5.4 Eptesicus fuscus 1 1.1 Peromyscus sp. 4 4.3 Sigmodon hispidus 14 15.2 Oryzomys palustris 1 1.1 Mus musculus 4 4.3 Rats and mice (unidentified) 15 16.3 Small rodents (total) 38 41.3 Sciurus carolinensis 5 5.4 Sciurus niger 1 1.1 Sciurus sp. 4 4.3 Sciurus (total) 10 10.9 Syhilagus aquaricus 1 1.1 Sylvilagus floridanus 1 1.1 Sylvilagus ap. 17 18.5 Sylvilagus (total) 19 20.7 Procyon lotor 1 1.1 AVES Colinus virginianus 7 7.6 Melanerpes carolinus 1 1.1 Rallus longirostris 1 1.1 Unidentified warbler * 1 1.1 Unidentified birds 2 2.2 REPTILIA Lygosoma laterale ** 2 2.2 Eumeces laticeps 1 1.1 Cnemidophorus sexlineatus 3 3.3 Prey item Source MAMMALIA Mammals (unidentified) Hamilton & Pollack (1955); Palmer & Braswell (1995) Eptesicus fuscus Anderson (1965) Peromyscus sp. Hamilton & Pollack (1955); Brown (1979) Sigmodon hispidus Hamilton & Pollack (1955); Palmer & Braswell (1995); Anderson (1965); this study Oryzomys palustris Palmer & Braswell (1995) Mus musculus Palmer & Braswell (1995) Rats and mice (unidentified) Grant (1970): Clark (1949) Small rodents (total) Palmer & Braswell (1995); Brown Sciurus carolinensis (1979); Goodrum (1940) Sciurus niger Dundee & Rossman (1989) Klauber (1956); Clark (1949); Sciurus sp. Zipperer (1947) Sciurus (total) Syhilagus aquaricus Dundee & Rossman (1989) Sylvilagus floridanus Klauber (1956) Hamilton & Pollack (1955); Klauber Sylvilagus ap. (1956); Palmer & Braswell (1995); Clark (1949) Sylvilagus (total) Procyon lotor Martin & Wood (1955) AVES Colinus virginianus Palmer & Braswell (1995); Clark (1949); this study Melanerpes carolinus Hamilton & Pollack (1955) Rallus longirostris Grant (1970) Unidentified warbler * Palmer & Braswell (1995) Unidentified birds Hamilton & Pollack (1955); Palmer & Braswell (1995) REPTILIA Lygosoma laterale ** Hamilton & Pollack (1955) Eumeces laticeps Hamilton & Pollack (1955) Cnemidophorus sexlineatus Hamilton & Pollack (1955) (*)Identification based on feathers. Most likely American redstart (Setophaga ruticilla). (**)= Scincella lateralis.
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|Author:||Platt, Steven G.; Hawkes, Anthony W.; Rainwater, Thomas R.|
|Publication:||The Texas Journal of Science|
|Article Type:||Statistical Data Included|
|Date:||May 1, 2001|
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