Snake Size Research Articles

Ontogeny of intersexual head shape and prey selection in the pitviper Agkistrodon piscivorus

Different animal intraspecific classes commonly differ in their prey selection. Such differences in feeding ecology are thought to reduce resource competition between classes, but other factors (i.e. behavioural, morphological, and physiological differences) also contribute to this widespread phenomenon. Although several studies have correlated the size of the feeding apparatus with prey selection in many animals, few studies have examined how the shape of the feeding apparatus is related to prey selection. Furthermore, even though the dietary regimen of many animals changes during ontogeny, few studies have examined how shape changes in the feeding apparatus may be related to these ontogenetic dietary shifts. Here we address these issues by examining how head shape, head size and prey selection change over ontogeny in adult males, adult females and juveniles of the cottonmouth snake Agkistrodon piscivorus. Our scaling data for head characteristics showed that all head measurements in adult male and female A. piscivorus scaled with significant negative allometry, whereas juvenile head measurements typically scaled isometrically, except for head volume (positive) and head length (negative). Thus, juveniles have relatively broad and high, but short, heads. Large adult male and female A. piscivorus have relatively small head dimensions overall. Thus, juveniles appear to undergo a rapid change in head volume, which subsequently slows considerably as sexual maturity is achieved. However, our multivariate analysis of size-adjusted head dimensions showed that juveniles differed only slightly in their head shape compared with adult male and female A. piscivorus. In general, prey size increased with snake size across all age and sex groups, but an ontogenetic shift in prey type was not detected in either males or females. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 151‐159.

Body size plasticity and local variation of relative head and body size sexual dimorphism in garter snakes (Thamnophis sirtalis)

AbstractFor snakes, prey size and sex are two possible determinants of head and body size. In garter snakes Thamnophis sirtalis, females are generally longer and have greater body weights than males, and also have larger relative head sizes, which may facilitate foraging success. The selective pressures that account for sexual size dimorphism in garter snakes have not been unequivocally demonstrated. In this study, the body (length and mass) and head (head length, head width, jaw length, inter‐ocular distance) sizes of garter snakes inhabiting two nearby but ecologically dissimilar sites with different types of available prey were compared. Overall, the adult female snakes were larger and had greater relative head sizes than males. Males from the two sites did not differ significantly in body or head sizes. However, the mean body length and mass of females from a site where vertebrates are included in the diet were greater than that of females feeding almost exclusively on earthworms. There were also significant site differences in all four head measurements in females, although the direction of the difference varied by site. Diet‐induced morphological plasticity is well documented and was evident in this study, although the relative roles of genotype, ontogeny, and competing selective forces in the expression of such plasticity can only be ascertained through future experimental studies.

Seasonal and Prey-size Dietary Patterns of Black Ratsnakes (Elaphe obsoleta obsoleta)

Black ratsnakes (Elaphe obsoleta obsoleta) prey extensively on both birds (eggs and nestlings) and mammals. There is conflicting evidence, however, regarding whether the snakes specialize on birds during the birds' nesting season or whether predation on birds is opportunistic. We tested these alternatives by determining seasonal dietary patterns from 81 fecal samples collected from black ratsnakes in eastern Ontario over 4 y. We also used these data to determine how diet varies with snake size. Birds occurred in the snakes' diet from May through August, but the occurrence of birds never exceeded that of mammals in any month. This pattern was the same as that previously reported for black ratsnakes in Kansas and supports the hypothesis that black ratsnakes prey on birds opportunistically. Relative to smaller individuals, larger ratsnakes preyed on larger species of mammals and reduced their consumption of smaller species of mammals. The reduction in the consumption of small prey by large snakes was due to diet diversification rather than specialization. However, because larger snakes continued to include small prey in their diet, predation patterns on birds and mammals suggest that ratsnakes are opportunistic predators.

Antipredator responses of California ground squirrels to rattlesnakes and rattling sounds: the roles of sex, reproductive parity, and offspring age in assessment and decision-making rules

California ground squirrels (Spermophilus beecheyi) and northern Pacific rattlesnakes (Crotalus viridus oreganus) have an adversarial relationship. Adults are partially protected by venom resistance and harass rattlesnakes in part to defend their more vulnerable offspring. Larger, warmer snakes are more dangerous than smaller colder snakes, and in escalated conflict squirrels could benefit from risk assessment strategies. Rattlesnakes often rattle at harassing squirrels and rattling sounds produce cues related to body size and temperature. In study 1 we played back rattling sounds from snakes that varied in dangerousness and evaluated the roles of sex and parity in squirrel risk assessment strategies. In general, squirrels tail flagged and stood bipedally more, and were slower to reapproach the playback speaker following playbacks of rattling sounds from more dangerous snakes. In comparison with males and nonmothers, mothers were most responsive to rattling sounds and more sensitive to variation in snake dangerousness. Mothers tail flagged more than males and nonmothers, and this behavior tracked variation in snake dangerousness most closely, perhaps reflecting the effects of snake size and temperature on pup vulnerability. These findings suggest that many aspects of squirrel antisnake behavior are governed by their effects on descendant kin. In study 2 we tested the effects of offspring age on mothers’ responses to live rattlesnakes and rattling sounds. According to the offspring value hypothesis, mothers should take more risks in defense of older offspring because they are more likely to survive to reproductive age. By contrast, under the offspring vulnerability hypothesis, older offspring are less vulnerable to predators and thus mothers should take fewer risks. Risk-taking, as measured by behaviors that bring the squirrel close to the snake’s strike range, was either unaffected by or negatively correlated with offspring age. Thus, our findings suggest that whereas offspring value is unimportant in squirrel antisnake behavior, offspring vulnerability may affect maternal defense. We suggest that offspring vulnerability in mammals, in comparison with birds, may play a larger role in parental defense against predators.

Body Size Evolution in Snakes: Evidence from Island Populations

The current literature reports divergent conclusions on the patterns of body size change in island snakes. I reviewed body size data in the published literature and tested the effects of island biogeographic variables on such changes. I found that none of the physiographic variables (island area, island age, distance to mainland, and latitude) was important in determining changes in size of island snakes. Additionally, a current hypothesis of phylogenetic history had no effect on changes in body size. Rather, the proportional change in body size of island snakes was bimodal, consistent with a diet alteration hypothesis that suggests that snake body size is principally influenced by prey size and that island snakes encounter prey that are larger or smaller in size compared with those on the mainland. Also, snakes that became small on islands did so to a relatively greater degree than those that became large. Ontogenetic changes in foraging strategies appeared to explain this pattern. The distribution of gigantic and dwarf snake populations on islands differed significantly between the families Viperidae and Colubridae. The foraging style of colubrids, specifically nest-robbing behavior, may predispose these species to become larger on islands. Numerous colubrid (and one elapid) species attain their largest sizes on islands that also support nesting seabirds, whereas dwarfed populations consume mainly squamates.

Influence of thyroid hormones on the thermal selection of African house snakes (Lamprophis fuliginosus)

1. Neither thyroxine (T4) nor triiodothyronine (T3) significantly influenced mean preferred body temperature (Tb) of African house snakes, Lamprophis fuliginosus. T4 tended to decrease mean preferred Tb while T3 slightly increased preferred Tb. Although these results contrast with earlier evidence indicating significant influences of thyroid hormones on Tb, they support earlier observations suggesting independent roles for T4 and T3 in the modulation of thermoregulatory behavior.2. Male and female snakes showed a similar lack of response to thyroid hormone treatments. However, the small sample size of male and female snakes (n=4 for each) within each treatment limits the power of these analyses for sex differences.3. Mean selected Tb's of African house snakes in response to hormone treatments also did not differ among phases of the photoperiod.4. We found no statistically significant differences between the thermoregulatory behaviors of snakes receiving injected control (5% ethanol in reptile Ringer's solution) and non-injected control treatments. These results have important implications for studies attempting to relate experimental manipulation (via intraperitoneal injection) of study animals to natural endogenous conditions.

Predicted and observed maximum prey size – snake size allometry

Summary For gape‐limited predators such as snakes, it should be possible to predict the relationship between maximum prey size and body size from the relationship between maximum prey size and gape size and between gape size and body size. Such predictions were generated for Water Snakes, Nerodia sipedon L., using a data subset and then tested with a larger data set. Gape size was computed based on jaw length and width and cyclical regression was used to identify prey of maximum size for snakes of a given gape or mass. Predicted and observed maximum prey cross‐section–snake mass allometry were in good agreement. Predicted maximum prey mass–snake mass allometry somewhat exceeded observed allometry which did not differ from 1. Observed minimum prey size–snake size allometry was significantly greater than 0, indicating that larger snakes drop small prey from their diets. Gape size–body size allometry in two other natricine snakes (Thamnophis sirtalis, Storeria dekayi) suggest that patterns of ontogenetic change in prey size should differ among species in predictable ways. Sex differences in gape size–snake size allometry suggest that sex differences in maximum prey size should increase with increasing snake size, even when linear measures of head dimensions do not.

Philopatry and Homing Behavior of Sea Snakes (Laticauda colubrina) from Two Adjacent Islands in Fiji

Abstract: The spatial scale at which anthropogenic disturbance affects an animal population depends on the degree of philopatry and homing of individual organisms within that population. Even in highly vagile species, local populations may comprise ecologically separate entities if most animals display strong and consistent site attachment. We conducted a mark‐recapture study on yellow‐lipped sea kraits ( Laticauda colubrina) on two small Fijian islands separated by 5.3 km. These snakes forage over many kilometers in the ocean, but return to land to reproduce, slough, and digest their food. Recovery of marked snakes showed that the populations on these two islands were essentially separate. Relocated snakes returned “home” almost immediately after they were released. Growth rates and mean adult body sizes of male sea snakes also differed between the two islands. This high site fidelity means that activities such as resort development or commercial harvesting for the skin trade are likely to have intense localized effects rather than diffuse broad‐scale effects on sea snake populations. Our results also call into question the feasibility of plans to reintroduce snake populations to areas where a species has been eliminated by overexploitation.

Relationships between sexual dimorphism and niche partitioning within a clade of sea-snakes (Laticaudinae)

Previous studies in Fiji have shown that females of the amphibious sea-krait Laticauda colubrina are much larger than males, and have larger heads relative to body size. The dimorphism has been interpreted in terms of adaptation to a sex divergence in prey-size: females primarily eat large (conger) eels rather than smaller (moray) eels. The hypothesis that dimorphism is affected by niche divergence predicts that the degree of sex dimorphism will shift when such a species invades a habitat with a different range of potential prey sizes. On the island of Efate in Vanuatu, L. colubrina and a regionally endemic sibling species (L. frontalis) both consume smaller eels (in absolute terms, and relative to the snake's body size) than do the previously-studied Fijian snakes. Patterns of morphology and sexual dimorphism have shifted also. Both Vanuatu taxa are slender-bodied, and frontalis is smaller and less dimorphic than L. colubrina. Females grow larger than males in all taxa, and have larger heads (relative to body length), but the degree of sexual divergence is lower in Vanuatu (especially in frontalis). Dietary overlap (in prey species as well as size) is high between adult frontalis and juvenile colubrina, but the two taxa differ in prey size/predator size relationships. In particular, male frontalis eat very small prey and have very short heads. Our results are consistent with the hypothesis that sex differences in the mean adult body sizes and relative head sizes of laticaudine snakes are linked to sex differences in feeding biology.

The role of the midland water snake, Nerodia sipedon (Serpentes: Colubridae), as a predator: foraging behavior, kin recognition, and the response of prey

AbstractThe midland water snake, Nerodia sipedon, is very abundant in portions of the southeastern U.S.A., where it may play an important role as a predator in freshwater communities. I examined whether foraging mode in naïve neonatal snakes was phenotypically plastic or canalized and I compared handling times and capture efficiencies for different prey types (juvenile fishes and frogs) between neonatal and adult snakes. I also tested for kin recognition by mother snakes by comparing their consumption of unrelated (non-kin) and related (kin) neonates according to time and the availability of alternative prey (fish). In addition, the response of prey in the presence and in the absence of snakes was tested by comparing the amount of time that juvenile fishes utilized areas containing different microhabitat complexities and by comparing the amount of time that fishes were actively moving. Overall, foraging mode was phenotypically plastic, handling times and capture efficiencies differed by prey type and snake size class, kin recognition was confirmed, and fishes did not alter their habitat selection or activity patterns in the presence of snakes.

A direct comparison of trapping and spotlight searches for capturing Brown Tree Snakes on Guam

Brown Tree Snake populations on Guam are controlled in the vicinities of cargo staging and transport areas to prevent their dispersal from Guam, and their populations are controlled in areas where endangered species are to be reintroduced. Trapping and night-time spotlight searches of fences are the two primary Brown Tree Snake population reduction methods used on Guam. We conducted a three month study comparing Brown Tree Snake captures by spotlighting fences to captures by trapping. Traps were placed either on the edge of the forest paralleling the fences, or they were hung on the fences. Applications of each capture method followed the standard practices used within the operational programme charged with deterring the spread of Brown Tree Snakes from Guam. We found captures by trapping to exceed those by spotlighting each month, but the captures by trapping decreased substantially over time, while those by spotlighting did not. We detected no differences statistically between numbers of captures taken by traps hung on the forest edge versus those hung on the fences. We found no differences in sizes of Brown Tree Snakes captured by spotlighting and trapping, based on average snout-vent length (SVL) or the distribution of SVLs. We feel that the two capture methods complement each other in an integrated pest management programme.

Behavioural responses by hatchling racers (Coluber constrictor) from two geographically distinct populations to chemical stimuli from potential prey and predators

AbstractIn experiments on responses to chemical food stimuli by previously unfed hatchlings from widely separated populations of the colubrid snake Coluber constrictor in the United States, strong responses were elicited by items important in the local diet. These differed between populations, suggesting that response has been adjusted to local diet by natural selection. Coluber constrictor priapus from South Carolina tongue-flicked at elevated rates to cues from lizards, snakes, and frogs, and bit only in response to a preferred lizard prey. They responded more strongly to the sympatric lizard Anolis carolinensis than to A. sagrei, an allopatric congener. Strong response to cues from the ophidiophagous snake Lampropeltis triangulum might reflect motivation for predator avoidance or for feeding, depending on relative snake sizes. Coluber constrictor mormon, for which insects and mammals are the most important foods, responded most strongly to stimuli from sympatric insects, mammals, and a lizard, as well as a bird.

Conflict and assessment in a predator–prey system: ground squirrels versus rattlesnakes

Adult California ground squirrels,Spermophilus beecheyi beecheyi, actively confront and harass northern Pacific rattlesnakes,Crotalus viridis oreganus, which are the principal predator of ground squirrel pups. In this report we examine the roles of risk (snake size) and context (location of encounter and squirrel reproductive category) in rattlesnake assessment by ground squirrels. In interpreting the results, we borrow heavily from the well-developed conceptual framework applied in the analogous case of intraspecific conflict. Large and small snakes were tethered near the home burrows of male ground squirrels, and maternal and nonmaternal female ground squirrels. Ground squirrels appeared to employ assessment strategies which served to mediate the level of risk associated with confronting larger snakes. The results suggest that ground squirrels exercise greater caution when dealing with large snakes and invest more in monitoring the snake from a safe distance. Maternal squirrels, which have more at stake reproductively, spent more time and effort in snake-directed activities than did squirrels from other reproductive categories. Mothers also differentiated more strongly between large and small snakes, perhaps reflecting the greater vulnerability of their pups to larger snakes. Finally, ground squirrels discriminated between snakes found close to their home burrow and those encountered further abroad. At the home burrow, squirrels monitored the snake from a closer distance, displayed a greater willingness to confront the snake, and escalated to more dangerous levels of harassment. This assessment strategy may reflect a higher payoff to squirrels that persist in driving snakes out of the home area, thereby reducing the risk of future ambush.

A study on the venom yield of venomous snake species from Argentina

A study on the venom yield of snakes from Argentina over a three year period was carried out on adult specimens of Bothrops alternatus ( n=74); Bothrops neuwiedii ( n=127); Bothrops ammodytoides ( n=30); Bothrops moojeni ( n=14); Bothrops jararaca ( n=14); B. jararacussu ( n=6); Crotalus durissus terrificus ( n=120) and Micrurus spp. ( n=6) as well as with 12 specimens of newborn C. d. terrificus kept in captivity. While for each species there was a positive correlation between venom yield and number of snakes milked, the correlation with the snake's body weights after individual milkings was even better, suggesting that the size of the snakes is more important in determining the venom yield than the number of snakes milked or the specimen's sex. Individual milkings indicated that, in addition to the snake size, when the amount of venom is normalized per 100 g body weight there is a species specific difference in venom yield. It follows the order B. jararacussu> B. moojeni≅ B. jararaca≅ B. alternatus> B. neuwiedii> Micrurus spp≅ B. ammodytoides> C. d. terrificus. Although the venom yield per 100 g body weight of newborn C. d. terrificus specimens is 2-fold higher than that of adults, no correlation was observed between venom yield and body weight.

A neglected life‐history trait: clutch‐size variance in snakes

Most analyses of life‐history traits have focused on mean values rather than their associated variance. We review published and original data on snakes, including records gathered over many years on single populations, to examine patterns in clutch‐size variability in these animals. Within single populations, the coefficient of variation of clutch size did not vary significantly with maternal body size, or among years. The stability of clutch‐size variance through time is consistent with experimental studies showing no significant influence of food intake rates on this characteristic. Clutch‐size variances did not differ between viviparous and oviparous snakes, but were dependent upon allometric relationships involving maternal body size and the relationship between clutch size and body size. Clutch‐size variability was highest in species with relatively variable female sizes, and with a high rate of increase in clutch size with increasing body size. These two factors acted to magnify the extent of clutch‐size variability engendered by variability in maternal body sizes. The relationships among these variables were similar in the two squamate Suborders, but the larger body sizes and mean clutch sizes of snakes resulted in clutch‐size variances being higher in snakes than in lizards.

Predation by grass snakes (Natrix natrix) at a site in southern England

The prey and feeding frequency in free‐living grass snakes was studied during 1993 and 1994 at a site in southern England. Individual snakes and common toads were recognized using PIT tags and a small number of adult snakes were radio‐tracked over long periods to determine predation rates.Grass snakes fed, almost exclusively, on common toads (adult, juvenile, and tadpoles). A positive correlation was found between prey size and snake size. Large snakes did not appear to prey upon small toads, although clearly capable of doing so.Male and female snakes ate large meals (toads) approximately every 20 days between May and September, with females fasting for a period of about 45 days during gestation and egg‐laying. After allowing for differences in the number and size of toads predated by male and female snakes, the mean amount of food consumed per day was estimated to be 2.3% and 1.6% of body weight.

Smallest maximal snakes of translates of convex domains

LetK be a convex domain. A maximal snake of sizen is a set of non-overlapping translatesK1, ...,K N ofK, whereK i touchesK j if and only if |i −j|=1 and no translate ofK can touchK1 orK n without intersecting an additionalK i ,i=1, ...,n. The size of the smallest maximal snake is proved to be 11 ifK is a parallelogram and to be 10 otherwise.

PHENOTYPIC PLASTICITY IN BODY SIZES AND SEXUAL SIZE DIMORPHISM IN EUROPEAN GRASS SNAKES.

Many animal species show considerable geographic variation in average adult body sizes. Although this phenomenon offers a unique opportunity to tease apart the factors influencing body size, interpretation has proved to be difficult because several processes may contribute to the observed variation (e.g., Andrews, 1976; Case, 1978; Dunham et al., 1978). First, average body size is influenced by adult survival rates in species in which growth continues after maturity: animals may be smaller in one area than another simply because they are, on average, younger (e.g., King, 1989). Second, even if survivorships are similar among areas, so that the body-size differences are due to differences in growth patterns, there are two possible explanations for such variation in growth. Body sizes may differ either because of local genetic modifications (possibly due to adaptation) or because of a direct phenotypic effect of differing food availability on growth rates (e.g., Berry et al., 1987; Dobson and Murie, 1987; Ebenhard, 1 990). To distinguish among these alternative interpretations, we need two kinds of data on growth trajectories of animals: first from the field (to determine whether the populations differ in actual growth patterns, rather than simply survivorships) and second the response to experimental manipulation of food supply (to determine whether the observed differences in growth rates are due to genetic differences or phenotypic plasticity). This paper presents information on European grass snakes. We show that body sizes and the degree of sexual difference in body size are greatly reduced in an island population compared to the nearby mainland, that these differences are due to modified growth patterns and not just survivorship, and that the low growth rates and small asymptotic body sizes of the island snakes are a phenotypic response to local conditions (probably, low food availability). Insular populations of snakes offer some of the most dramatic examples of geographic variation in body size (e.g., Case, 1978; Schwaner, 1985; King, 1989; Shine, 1987; Schwaner and Sarre, 1988; Hasegawa and Moriguchi, 1989; Forsman, 1991). For example, Schwaner (1985) showed that body masses of adult Australian tigersnakes varied up to tenfold among adjacent islands. Correlational analyses suggest that predators attain larger sizes in areas where larger species of prey are available, and this may be true both for snakes (Schwaner, 1985; Hasegawa and Moriguchi, 1989) and for mammalian predators (Gittleman, 1985; Erlinge, 1987). Experimental studies on mammals have shown that geographic variation in body sizes may be due both to phenotypic plasticity (e.g., Dobson and Murie, 1987) and to local adaptation (e.g., Berry et al., 1987; Ebenhard, 1990). The only experimental study to address the determinants of such differences in snakes has been that of Barnett and Schwaner (1984), who raised juvenile tigersnakes. These authors documented rapid growth in captive snakes from a giant population, but obtained no comparable information on snakes from dwarf populations. We studied two populations of a nonvenomous natricine colubrid species, the grass snake (Natrix natrix), which is abundant over much of Europe (Arnold and Burton, 1978). The mainland study area was near Maryd, 15 km south of Lund in southern Sweden (55?40'N, 13?30'E). The area contains a mixture of arable land, grazed meadow, and mixed deciduous forest. Detailed data have already been published on body sizes, sexual size dimorphism, growth rates, diets and reproductive biology of grass snakes from this area (Madsen, 1983, 1987). Those papers also describe the methods used to capture, mark and measure snakes, and to obtain prey items by forced regurgitation. The same methods were used for the study of island snakes. Our island population was on Hallands Vadero (56?27'N, 12?44'E), a small (2.6 kM2) island approximately 3 km from the Swedish coast. One quarter of the island is forested, with the remainder consisting of meadows bordered by blackthorn, stony areas with juniper, and bare rock (Madsen and Stille, 1988). The two study areas are approximately 100 km apart. Geological evidence suggests that the two areas probably have been separated for several thousand years, since glaciation-induced reductions in sea level (Devoy, 1987). However, it is possible that the effective period of separation may have been longer than this (e.g., these oviparous snakes may not have existed in this region during glacial periods) or considerably briefer (due to fortuitous dispersal of snakes from one area to another). Male snakes from the island were similar to the mainland animals in mean SVL (Fig. 1; N = 22, 41; means = 52.2 versus 53.0 cm, t = 0.40, df= 61, P = 0.69) but females were much smaller on the island (N = 28, 44; means 59.7 versus 69.9 cm, t = 4.14, df= 70, P < 0.001). Indeed, some male snakes from the mainland actually attained larger sizes than did any of the females from the island population, although the mean values were lower (Fig. 1). Two-factor analysis

On the smallest limited snake of unit disks

A limited snake of size n is a set of nonoverlapping unit disks D 1, ..., D nwith centers c 1, ..., c nwhere the distances ¦c i c j¦=2 if and only if ¦i−j¦=1, and no disk can touch D 1 or D nwithout further common points with D 1, ..., D nThe size of the smallest limited snake is proved to be 10.

Sources of Variation in Estimating Litter Characteristics of the Garter Snake, Thamnophis elegans

--Studies of snake demography usually involve the estimation of litter size and neonate size, but potential sources of variation resulting from the methods used to obtain this information are rarely considered. Using data from four populations of Thamnophis elegans, we found that estimates of litter size obtained by holding gravid snakes in captivity were less variable when dead young or undeveloped eggs were included rather than excluded; we recommend that all components of litters be reported in future studies. Litter sizes obtained by palpation of gravid snakes in the field were similar to estimates from captive births in two of three populations we examined, but not the third. There was some evidence that litters from longer-term captives were more likely to contain dead young, and, in one population, smaller young. Access to substrate heat by gravid snakes was correlated with smaller progeny in another population. In general, captive-born snakes were smaller than neonates born in the field, but some growth may have occurred in the latter. Factors that might influence the size of snakes born in captivity are temperature, feeding level of mother, and stress; in order to minimize their potential effects, we recommend that gravid snakes be held for as short a time as possible. The study of life history variation in snakes has lagged behind that of other kinds of organisms (Parker and Plummer, 1987), mainly because of the difficulties of sampling snake populations (Turner, 1977). Although field measurements of important parameters such as survivorship have rarely been measured adequately (Parker and Plummer, 1987), reports of clutch or litter size are abundant (Seigel and Ford, 1987). These data can be obtained by dissection of preserved specimens, gentle hand palpation of gravid snakes in the field, or holding gravid snakes in captivity until they have laid eggs or produced young. The accuracy of clutch or litter size estimates obtained by palpation is unclear, but with practice, embryos can usually be distinguished from one another and from lumps of fecal material within the large intestine (Fitch, 1987; Farr and Gregory, pers. obs.). Sometimes, especially in the later stages of gestation, embryos may be more difficult to distinguish from one another; an embryo and its yolk sac may also be felt as two separate lumps (Fitch, 1987). Difficulties such as these will influence estimates of litter