Snake Size Research Articles

Variation in size of cover used by watersnakes ( Nerodia): Do smaller snakes use smaller rocks?

Snakes often seek shelter under rocks or other physical cover objects, which provide protection from both predators and unfavourable weather and also may be used actively in thermoregulatory behaviour. Presumably, snakes are limited, by their own body size, to some minimum rock size, so that we should expect a positive relationship between a snake's size and the size of the rock it uses. I tested this hypothesis for the watersnake, Nerodia sipedon, along a creek in a peri-urban setting in southern Ontario, Canada. Although larger snakes tended to be found under larger rocks, the relationship was weak. A composite measure of rock size from PCA was not markedly better than simple rock length. Sizes of rocks used by snakes did not change over the active season. Snakes tended to be found under the largest rock in their immediate vicinity, but distances from used rocks to equally big or bigger rocks rarely exceeded a few metres. Similarly, measurements of rocks on transects along the creek showed that, although small rocks predominated, all transects contained rocks large enough for snakes. Thus, it seems unlikely that cover is limited for watersnakes at this site. However, unmeasured factors such as temperature or other physical characters of rocks could change that conclusion. These factors would best be determined by manipulative experiments.

Gastrointestinal responses to feeding in a frequently feeding colubrid snake ( Natrix maura)

Ectotherm vertebrates show physiological mechanisms that reduce metabolic costs during prolonged fasting. Once feeding, these animals adopt a wide variety of metabolic responses such as changes in gastrointestinal organ masses. Up-regulatory responses after feeding have been widely explored in infrequently feeding snakes like pythons, whereas few studies have been devoted to frequently feeding snakes. In this study, we have considered the gastrointestinal responses after feeding in a frequent feeder, the viperine snake Natrix maura, in the Ebro Delta rice fields. In this habitat, viperine snakes are exposed to long periods of food deprivation due to the lack of available prey as a consequence of the man-induced rice cycle. We weighed prey items and full gut masses, and measured length of combined esophagus and stomach, and intestine of viperine snakes belonging to a wide range of sizes. Snakes concentrate foraging activity when rice fields were flooded. In this period, gut masses increased. Likewise, intestines increased in length during the feeding period, which suggests that viperine snakes probably experience a postfeeding hypertrophy of their small intestines that contributes to their larger length. Once the intestine length was corrected for the snake size, it was shown that adults present longer intestines than immature snakes, reflecting an increase in the posterior part of the body linked to the gonads development. This study contributes to explore the physiological responses to feeding in frequently feeding snakes modelled by abrupt shifts of food availability.

Feeding and reproductive behavior of captive sea snakes Hydrophis cyanocinctus

The annulated sea snake ( Hydrophis cyanocinctus ) is a black and yellow banded neurotoxic hydrophiid, widely distributed along the Indian coast. Observations on the feeding and reproductive behavior of the snake were made for the first time in captivity. It consumed live or chopped fish; prey size depended on snake size. Breeding commenced in October and the matured neonates were observed during the following January. Twenty five gravid snakes gave birth to 87 neonates, i.e. 3-5 neonates per snake. During delivery, they exhibited a different type of movement to release the neonates, and all were delivered only at night. All neonates were measured the morphological traits of weight, snout-vent length, tail length, head length, head width, neck girth and body girth. The relative size of females and males differed significantly. But the relative size of tail length showed an opposite trend compared to other morphological traits. At the end of the experiment, the snakes and neonates were released in the open sea.

Diet of the rattlesnake Crotalus durissus in southeastern Brazil (Serpentes, Viperidae)

Gut contents of 633 live rattlesnakes from southeastern Brazil received at the Butantan Institute, SP, Brazil between 1993 and 1995 were studied. The snakes were weighed, measured and sexed. Two hundred and fifty‐nine rattlesnakes had stomach and/or intestinal contents. Prey size was estimated by comparison of prey items with specimens from museum collections. Rodents and small marsupials were the main prey eaten by the rattlesnakes, and only 1% of the items were found in the stomach, whereas 41% of the individuals in the sample had feces in the intestine. There was low correlation between size of snake and prey size. No seasonal difference in frequency was found between fed and not fed males, but the occurrence of fed females was significantly lower during summer than winter months (28.9% and 51.8%, respectively). Fed newborn rattlesnakes had the lowest frequency, and also fed on rodents. O conteúdo do trato digestivo de 633 cascavéis do sudeste brasileiro recebidas pelo Instituto Butantan, SP, Brasil entre 1993–1995 foram estudados. As serpentes foram pesadas, medidas e tiveram seu sexo determinado. Duzentas e cinqüenta e nove serpentes apresentaram conteúdo estomacal e/ou intestinal. O tamanho das presas foi estimado comparando‐os com espécimes de museu. Roedores e pequenos marsupiais foram as principais presas ingeridas pelas cascavéis, e somente 1% dos itens foram encontrados no estômago, entretanto 41% das cascavéis tinham fezes no trato intestinal. Houve pequena correlação entre o tamanho da serpente e da presa ingerida. Não foi observada diferença sazonal na freqüência de machos com e sem conteúdo, mas a ocorrência de fêmeas sem conteúdo foi significativamente menor nos meses de verão do que nos meses de inverno (28,9% e 51,8%, respectivamente). Cascavéis recém‐nascidas também se alimentam de roedores e têm a mais baixa taxa de animais com conteúdo.

Reproductive Biology of the Brown Tree Snake, Boiga irregularis (Reptilia: Colubridae), during Colonization of Guam and Comparison with That in Their Native Range1

ABSTRACT Since their introduction to Guam shortly after World War II, brown tree snakes, Boiga irregularis (Merrem), have seriously impacted the biota and human population of the island. Understanding the biology of this exotic species will likely be important to the success of control programs. We compared the reproductive biology of 782 B. irregularis caught on Guam during the 1980s with results from published studies of native-range populations. Average and maximum sizes of mature snakes on Guam were larger than those from Australian populations. The majority of female brown tree snakes matured at snout-vent lengths (SVLs) of 910–1,025 mm, and most males matured at SVLs of 940–1,030 mm on Guam. Based on growth rates from the early 1990s on Guam, sexual maturity is estimated to occur during a snake's third or fourth year. Only one female (0.3%) in our data set had oviductal eggs. Clutch size was estimated at 4.3 (SD = 2.2), based on large vitellogenic ovarian follicle (≥30 mm in length) and oviductal eg...

CAPTIVE BREEDING AND REPRODUCTIVE BIOLOGY OF THE Protobothrops cornutus AND Triceratolepidophis sieversorum

New data on the reproductive biology as well as results of the first captive breeding of very rare Asian pitvipers from Truongson Mountains: Protobothrops cornutus and Triceratolepidophis sieversorum are given. Characteristics of the reproductive biology of Protobothrops cornutus and Triceratolepidophis sieversorum , which are sympatric in Truongson Mountains (karst regions of Quang Binh Province) are discussed in the present paper. The data on copulation, gestation and incubation, clutches, size and weight of newborn snakes, temperatures during hibernation and the activity periods, temperature of incubation, a diet during different seasons for different age groups are given in the result of a successful breeding in the laboratory. The descriptions of size of eggs and structures of a shell are provided.

Parental care in the long-tailed skink, Mabuya longicaudata, on a tropical Asian island

Parental care has been reported in more than 140 species of reptiles (about 3%), but few records unambiguously demonstrate the selective value of that care. I experimentally investigated the influence of maternal attendance on survival of eggs in the long-tailed skink, Mabuya longicaudata, on Orchid Island, Taiwan, by placing sympatric reptiles, both predators and nonpredators, into nests. Without maternal care, most lizard eggs were eaten by the egg-eating snake, Oligodon formosanus. Female lizards with eggs attacked snakes more often and escaped from snakes less often than did females without eggs. Survival of eggs was lower when females were removed from clutches than when they were left in attendance. All egg loss in unprotected nests on Orchid Island was due to predation by O. formosanus. Size of snakes did not determine whether lizards abandoned egg-free nests or nests with eggs when attacked. Females that attacked egg predators had larger clutches than those that did not attack. Females recognized sympatric lizards and did not attack species that do not prey on eggs or on M. longicaudata, but recognized the predatory snake Elaphe carinata and escaped when that species entered the nest. These findings emphasize the ecological importance of an increased understanding of the function of parental care in reptiles.

Broad‐scale patterns of body size in squamate reptiles of Europe and North America

AbstractAim To document geographical interspecific patterns of body size of European and North American squamate reptile assemblages and explore the relationship between body size patterns and environmental gradients.Location North America and western Europe.Methods We processed distribution maps for native species of squamate reptiles to document interspecific spatial variation of body size at a grain size of 110 × 110 km. We also examined seven environmental variables linked to four hypotheses possibly influencing body size gradients. We used simple and multiple regression, evaluated using information theory, to identify the set of models best supported by the data.Results Europe is characterized by clear latitudinal trends in body size, whereas geographical variation in body size in North America is complex. There is a consistent association of mean body size with measures of ambient energy in both regions, although lizards increase in size northwards whereas snakes show the opposite pattern. Our best models accounted for almost 60% of the variation in body size of lizards and snakes within Europe, but the proportions of variance explained in North America were less than 20%.Main conclusions Although body size influences the energy balance of thermoregulating ectotherms, inconsistent biogeographical patterns and contrasting associations with energy in lizards and snakes suggest that no single mechanism can explain variation of reptile body size in the northern temperate zone.

Venom of the Brown Treesnake, Boiga irregularis: Ontogenetic shifts and taxa-specific toxicity

The Brown Treesnake ( Boiga irregularis), a rear-fanged member of the polyphyletic family Colubridae, is an introduced predator on Guam which has been responsible for numerous human envenomations. Because little is known about this species' venom, we characterized venom proteins from B. irregularis using enzyme assays, one and 2D electrophoresis, Western blot analysis, mass spectrometry, HPLC and toxicity assays. Venom yields and protein content varied significantly with snake size, and large adult specimens averaged over 500 μl venom (19.2 mg, protein content ∼90%). Only two enzymes, azocaseinolytic metalloprotease and acetylcholinesterase, were detected in venoms, and both activities increased with snake size/age. Western blot analysis demonstrated a 25 kDa CRiSP homolog in venoms from both neonate and adult snakes. 2D electrophoresis showed variation between venoms from neonate and adult snakes, especially with respect to metalloprotease and acetylcholinesterase. Analysis by MALDI-TOF mass spectrometry revealed the presence of numerous proteins with molecular masses of ∼8.5–11 kDa. Adult B. irregularis venom was quite toxic to domestic chickens ( Gallus domesticus; 1.75 μg/g) and lizards ( Hemidactylus geckos: 2.5 μg/g and Carlia skinks: 4.5 μg/g), and intoxication was characterized by rapid paralysis of all species and neck droop in chickens. Toxicity of venom from neonates toward geckos was 1.1 μg/g, consistent with the presence of a greater diversity of 8–11 kDa proteins (suspected neurotoxins) in these venoms. All of these values were notably lower than murine LD 50 values (neonate: 18 μg/g; adult: 31 μg/g). Like venoms of several front-fanged species, B. irregularis venom showed an ontogenetic shift in enzyme activities and toxicity, and neonate snakes produced more toxic venoms with lower protease and acetylcholinesterase activities. High toxicity toward non-mammalian prey demonstrated the presence of taxa-specific effects (and thus toxins) in B. irregularis venom, likely a characteristic of many colubrid snake venoms. We hypothesize that the lack of significant envenomation effects in humans following most colubrid bites results from this taxa-specific action of colubrid venom components, not from a lack of toxins.

Allometry and selection in a novel predator–prey system: Australian snakes and the invading cane toad

Because many organismal traits vary with body size, interactions between species can be affected by the respective body sizes of the participants. We focus on a novel predator–prey system involving an introduced, highly toxic anuran (the cane toad, Bufo marinus) and native Australian snakes. The chance of a snake dying after ingesting a toad depends on the size of the snake and the size of the toad, and ultimately reflects the effect of four allometries: (1) physiological tolerance (the rate that physiological tolerance to toad toxin changes with snake size); (2) swallowing ability (the rate that maximal ingestible toad size (i.e. snake head size) increases with snake body size); (3) prey size (the rate that prey size taken by snakes increases with snake head size) and (4) toad toxicity (the rate that toxicity increases with toad size). We measured these allometries, and combined them to estimate the rate at which a snake's resistance changes with toad toxicity. The parotoid glands (and thus, toxicity) of toads increased disproportionately with toad size (i.e. relative to body size, larger toads were more toxic) but simultaneously, head size relative to body size (and thus, maximal ingestible prey size relative to predator size) declined with increasing body size in snakes. Thus, these two allometries tended to cancel each other out. Physiological tolerance to toxins did not vary with snake body size. The end result was that across snake species, mean adult body size did not affect vulnerability. Within species, however, smaller predators were more vulnerable, because the intraspecific rate of decrease in relative head size of snakes was steeper than the rate of increase in toxicity of toads. Thus, toad invasion may cause disproportionate mortality of juvenile snakes, and adults of the sex with smaller mean adult body sizes.

Comparative Food Habits and Body Size of Five Populations of Elaphe quatuorlineata: the Effects of Habitat Variation, and the Consequences of Intersexual Body Size Dimorphism on Diet Divergence

The comparative diet and body size of the Four-Lined Snake (Elaphe quatuorlineata), one of the largest and more vulnerable species of snakes in Mediterranean central Italy, were studied in five different habitats. Data given here collated both literature and original data. Overall, females were significantly larger than males but the strength of these differences varied considerably with sample size. Overall, small mammals (almost exclusively rodents) accounted for the main part of the diet (66.7%), followed by birds and their eggs (mainly Passeriformes; 26.4%), and by lizards (6.9%), although the number of eggs in the diet was probably greatly underestimated. In qualitative terms, both sexes fed on the same prey types, but, quantitatively, males and females differed significantly in terms of prey composition; females fed on more birds and fewer lizards than males. Rodents were the most important prey source in most habitat types, although birds were preyed upon slightly more frequently in the wet habitat than rodents, which, nonetheless, still represented a important prey source. Four-Lined Snakes started feeding in early April and continued feeding until early November. The monthly frequency of occurrence of birds in snake stomachs differed significantly from that of small mammals; birds were taken almost exclusively in April and May (and mainly by females), and small mammals were taken all throughout the annual feeding cycle of snakes.

Universality in the merging dynamics of parametric active contours: a study in MRI based lung segmentation

Measurement of lung ventilation is one of the most reliable techniques in diagnosing pulmonary diseases. The time-consuming and bias-prone traditional methods using hyperpolarized H3He and 1H magnetic resonance imageries have recently been improved by an automated technique based on ‘multiple active contour evolution’. This method involves a simultaneous evolution of multiple initial conditions, called ‘snakes’, eventually leading to their ‘merging’ and is entirely independent of the shapes and sizes of snakes or other parametric details. The objective of this paper is to show, through a theoretical analysis, that the functional dynamics of merging as depicted in the active contour method has a direct analogue in statistical physics and this explains its ‘universality’. We show that the multiple active contour method has an universal scaling behaviour akin to that of classical nucleation in two spatial dimensions. We prove our point by comparing the numerically evaluated exponents with an equivalent thermodynamic model.

Population Structure, Body Size, and Seasonal Activity of Black Swamp Snakes (Seminatrix pygaea)

We examined the ecology of a Black Swamp Snake (Seminatrix pygaea) population inhabiting an isolated wetland in the upper Coastal Plain of South Carolina. The observed population structure was skewed towards mature individuals, with neonates and juveniles underrepresented, perhaps due to trapping bias. The sex ratio was biased during May and June, with females outnumbering males, but no sex ratio bias was evident at other times of the year. Seminatrix pygaea showed sexual dimorphism in body size, with females being longer and heavier than males and males having relatively longer tails than females, but there was no difference in monthly growth rates. Approximately 76.3% of the mature females captured in May and June 1998 were pregnant. Therefore, most mature females in this population probably exhibit annual reproduction, while some undergo biennial reproduction. The majority of females gave birth in July or August, with a few births occurring in September and October, and perhaps even as early as May or June. Our mark-recapture estimates suggest a population density greater than 60 adult snakes per hectare, which indicates this small aquatic snake, endemic to the Southeast, may play a large role as both predator and prey within isolated wetland ecosystems.

Relationships between body size, population abundance and niche characteristics in the communities of snakes from three habitats in southern Nigeria

The relationships between population abundance, body size, food habits and ecological guild (aquatic, terrestrial, arboreal, and fossorial) of snake communities are studied in three different habitats (swamp-rainforest, mangrove forest and derived savanna) of southern Nigeria, West Africa. There were slightly positive relationships between body size and population abundance of snakes in the three study habitats of tropical Nigeria, but statistical significance was reached only in the swamp-rainforest habitat. The population abundance of the various species was not related to either their food habits or their ecological guild in any of the three study areas. The possible reasons explaining these patterns are discussed. In general, there is little congruence between our data and the popular ‘energetic equivalence rule’ hypothesis.

A comparison of three trap designs for capturing brown treesnakes on Guam

The accidental introduction of the brown treesnake (Boiga irregularis) to Guam has resulted in the extirpation of most native terrestrial vertebrates on the island, thousands of power outages, and significant ecological changes. In addition, Guam now serves as a source population for the dispersal of snakes to other islands. Control of the brown treesnake is dependent upon the use of traps in a variety of settings, including port environments and in forested habitat. A variety of snake traps have been used on Guam; most consist of a modified crawfish or minnow trap, housing a live mouse that serves as a lure. We compared the efficacy of three trap styles: (1) a two-piece design with a separate internal mouse chamber; (2) a one-piece trap, with design improvements aimed at decreasing handling; and (3) the same one-piece trap, fitted with a PVC-coated wire-mesh entrance flap. Data collected included snake capture rates, snake size distribution, mouse survival, and trap maintenance time. Snake capture rates did not differ between the one-piece and the two-piece traps, although capture rates were significantly lower in the PVC-flap traps. The average snake size or distribution of snake sizes did not differ between the one-piece and two-piece traps. Handling times, both with and without a snake in the trap, were significantly lower for the one-piece trap. Mouse survival did not differ between the one-piece and two-piece trap styles. Our results indicate that the modified one-piece trap design provides several advantages over previous trap designs.

The effects of body size, age, and food intake during pregnancy on reproductive traits of a viviparous snake, Thamnophis ordinoides

:Litter characteristics of viviparous snakes presumably can be influenced by the mother’s state (e.g., mass) at the onset of pregnancy, by food acquired during vitellogenesis, or by food eaten by the mother during pregnancy and delivered to the developing embryos via the placenta. Alternatively, food consumed while pregnant could be allocated to the female herself, potentially influencing her future survivorship and/or reproduction. We tested the effects of food consumption during pregnancy on litter traits of the garter snake, Thamnophis ordinoides, along with the effects of body size and age of mother. We also measured trade-offs between traits. Age was significantly correlated with body size of female snakes, but it had no direct influence on reproductive traits. Initial body size, by contrast, especially snout-vent length, significantly and positively influenced litter size and mass. Food intake by gravid females declined during pregnancy, and snakes became relatively anorexic prior to giving birth; their appetite resumed following parturition. Snakes offered smaller amounts of food while pregnant ate less than those fed ad lib, but had similar postpartum appetites. Higher food intake during pregnancy resulted in higher postpartum mass of females, but not higher litter mass or size of offspring. There was strong evidence of a trade-off between litter size and offspring size and between postpartum mass and litter mass. Overall, our data are consistent with the hypothesis that reproductive traits of viviparous snakes are determined proximately by previously accumulated stores (capital) and/or food consumed during vitellogenesis (income), but not by resources acquired during pregnancy.

Geographic and Size-related Variation in the Diet of Insular Populations of the Northern Watersnake

I studied microgeographic and size-related variation in the diet composition of the Northern Watersnake Nerodia sipedon sipedon in the Beaver Archipelago of Lake Michigan. Snakes from Lake Michigan shoreline sites were piscivorous whereas snakes from interior sites on Beaver Island ate mostly amphibians. Sculpin (Cottus sp.) were the dominant prey of all size classes, but a gradual size-related shift in diet may be occurring in archipelago snakes. Large snakes tended to eat larger prey than small snakes and to drop the smallest prey from their diets, but overlap in prey size occurred among all size classes of snakes. The diet composition of snakes from different sites is likely a reflection of local differences in prey abundance, as found in several previous studies. The overlap in prey size and prey type among snake size classes contradicts the results of some previous studies of Nerodia sp. and merits further investigation.

Diet and Prey Size of the Flathead Snake, Tantilla gracilis

Diet and prey size relationships of Flathead Snakes (Tantilla gracilis) in the pine- hardwood forests of east Texas were determined on 68 individuals. Ninety-five percent of the snakes contained prey of which a large proportion was identifiable. Approximately 80% of the diet (by frequency) of T. gracilis consisted of coleopteran (beetle) larvae of the families Alleculidae, Elateridae, and Tenebrionidae. Other prey were centipedes and terrestrial snails. Correlation of prey size with snake size revealed a positive relationship, but accounts for little of the variation. Adults and juveniles ingested the same relative prey sizes with juvenile snakes predominately feeding on alleculid larvae and adults feeding on tenebrionid larvae. Larger snakes had a greater prey mass in their alimentary tracts; however, they did not consume significantly greater numbers of prey items. Direction of prey ingestion was primarily posterior first (72%). Because most of their prey have elongated bodies, it appears that T. gracilis responds to growth changes in body size by switching to different prey types. Choosing prey by size may be less important than prey shape for T. gracilis because of the morphological adaptations associated with a fossorial existence.

Diet and Feeding Behavior of Helicops infrataeniatus (Serpentes: Colubridae: Xenodontinae) in Southern Brazil

Analysis of the gut contents of 278 specimens of Helicops infrataeniatus from the eastern Central Depression of Rio Grande do Sul state, Brazil, indicates that this species feeds on fish and frogs. Fish were found in 60.0% and amphibians in 40.0% of the specimens with identifiable stomach and/or intestine content (n = 34). Fish corresponded to 69.5% and amphibians to 30.5% of the consumed items. Representatives of seven families and 10 genera of fish, from diverse microhabitats were identified. Among the amphibians, metamorphosed leptodactylids (two species of Leptodactylus and one of Pseudopaludicola) and a hylid tadpole were found. These data and field observations indicate that the species may forage in several water strata and at water's edge, during the day and/or at night. The predator–prey size relationship is weak, but positive and significant (r 2 = 0.3228, P < 0.001), indicating that large individuals of H. infrataeniatus generally ingest larger prey items. Eighty seven percent of the prey had a total length from 5 to 15% of the snout-vent length of the snakes that ingested them. Large prey, relative to snake size, were generally swallowed headfirst, whereas relatively small prey were swallowed head or tail first. The single exception was a large elongate (ophioform) fish without spiny fins: an easily swallowable and harmless prey, that was swallowed tail-first.

Food Habits of the Grass Snake in Southeastern England: Is Natrix natrix a Generalist Predator?

Generalist species are often both widely distributed and abundant. They also are often plastic in their ecology, both spatially and temporally, in response to variation in resources. Here, we study the food habits of the widespread European Grass Snake, Natrix natrix, in Kent in southeastern England. As elsewhere in their range, Grass Snakes at our study site mainly ate anurans (63%); however, small mammals also were fairly common in the diet (25%) and fish (10%) and birds (1%) were taken occasionally. About 65% of prey eaten by snakes were swallowed headfirst, but orientation of prey during ingestion varied among prey types. Although anurans are the major prey of Grass Snakes, the predominant species in their diet varies geographically, presumably in relation to availability; at our site, the most frequently eaten species (63%) was the introduced Marsh Frog, Rana ridibunda, which is very common and possibly influences abundance of snakes. We obtained few data on feeding habits of small snakes (< 400 mm SVL) but found anuran prey in the smallest snake in our sample; other prey types were eaten by larger snakes and therefore presumably are added to the diet as snakes grow. Maximum size of prey increased with snake size, but large snakes nonetheless continued to eat small prey as well. However, because Grass Snakes are sexually dimorphic (females larger), such size effects may be confounded with sex effects. Snakes had food in their stomachs less frequently in midsummer than they did in early and late summer. Nonetheless, even after adjusting for such seasonal variation, gravid females contained food less frequently than nongravid females. Thus, gravid females of this oviparous species apparently exhibit an anorexia similar to that seen in pregnant females of many viviparous species.