Juvenile Snakes Research Articles

A field study of spatial ecology and movements of a threatened snake species, Hoplocephalus bungaroides

Information on movement patterns, home range sizes and site fidelity of endangered fauna may provide a basis for conservation planning (size and location of reserves; vulnerability to habitat fragmentation; feasibility of natural recolonisation of ‘restored’ habitats, etc.). To obtain such information, we surgically implanted miniature radio transmitters in 25 individual broad-headed snakes Hoplocephalus bungaroides, a small (mean snout-vent length = 57 cm, mean mass = 51 g) viviparous elapid snake reliant upon sandstone outcrops in southeastern Australia. We also carried out a mark-recapture study of this threatened species. Our telemetered snakes spent long periods of time sequestered inside retreat-sites (rocks, crevices, tree hollows) and thus were active on only 21% of days. Gravid females had small home ranges (mean size = 0·05 ha, convex polygon method) and remained near cliffs during summer, whereas most males and non-gravid females moved long distances (up to 780 m) away from cliff tops during summer and had larger home ranges (mean size = 3·3 ha). Movements by the snakes were more frequent and extensive when they were in the woodland (mean interval between successive moves = 2·9 days; mean displacement per move = 159 m) than when they were in the rock outcrops (means = 6·3 days, 37 m). Home ranges were larger in summer than in spring, and were larger in 1994–95 than in other years. Home ranges of males showed little spatial or temporal overlap in spring, but females were found within the areas used by males. During summer there was little temporal or spatial overlap of home ranges of adults, which suggests that snakes may actively avoid conspecifics of either sex while foraging in the forest. Many adult snakes showed strong site fidelity, frequently returning to the same rocks where they were initially captured. Dispersal of juvenile snakes from their birth sites was relatively limited (maximum recorded distance = 375 m after 6 months). Our results have significant implications for conservation of this threatened taxon. The fixed home ranges and high site fidelity of adults coupled with the low dispersal rates of juvenile broad-headed snakes mitigate against successful natural recolonisation of rehabilitated habitats. Thus, habitat restoration may need to be combined with release of captive-bred progeny, or field-caught neonates. The exclusive home ranges of adult snakes suggest that social interactions (avoidance of conspecifics) may limit population densities, and hence that (i) removal of some neonates may not reduce future densities of adults, and (ii) habitat destruction is likely to be a more serious long-term threat than removal or killing of individual snakes. The large home ranges, and frequent and extensive movements, of snakes in woodland indicate that conservation reserves must incorporate large forest areas adjacent to sandstone outcrops.

An Experimental Test for Food Effects on Head Size Allometry in Juvenile Snakes

An Experimental Test for Food Effects on Head Size Allometry in Juvenile Snakes

Resource dependent growth and body condition dynamics in juvenile snakes: an experiment.

We examined the manner in which animals adjust the proportion of energy allocated to growth and storage in response to food availability. We compared univariate growth and length-mass relationships between juvenile adders (Vipera berus) reared under two different feeding regimes. Animals in the low- and high-food experimental groups were fed suckling mice once and twice weekly, respectively. Snout-vent length, body mass, and body condition (residual scores from log-log regression of body mass on snout-vent length) were measured shortly after birth, and at 4, 9, and 14 weeks. We found that growth in length and mass, as well as changes in length-mass relationships, differed between treatments; snakes with access to more food not only increased faster in length but were also heavier at the completion of the experiment than were similar sized less frequently fed snakes. There was no association between body condition of individuals measured at birth and at the end of the experiment, whereas size at birth was a good predictor of final size. Our results provide evidence for resource-dependent allocation strategies in V. berus, and suggest that somatic growth is less sensitive to environmental fluctuations than body condition, presumably because body size is of greater importance for fitness.

Predation by snakes on seabirds at three South African islands

During 1989–1994, adult mole snakes Pseudaspis cana at Robben Island were recorded eating eggs of African penguin Spheniscus demersus and Hartlaub's gull Larus hartlaubii, as well as those of helmeted guinea-fowl Numida meleagris. Juvenile mole snakes ate clicking stream frogs Strongylopus grayii. At Schaapen and Meeuw islands, egg-eater snakes Dasypeltis scabra fed on eggs of Cape cormorant Phalacrocorax capensis, kelp gull L. dominicanus and rock pigeon Columba guinea. A puff adder Bitis arietans was seen at Meeuw Island, but was not observed feeding there.

COLOR-PATTERN VARIATION IN LAKE ERIE WATER SNAKES: PREDICTION AND MEASUREMENT OF NATURAL SELECTION

A classic example of natural selection, that of color-pattern variation in Lake Erie island populations of water snakes, was reexamined to overcome shortcomings resulting from classification of snakes into discrete color-pattern categories and use of cross-sectional data. Four continuously varying color-pattern components (DB, the number of dorsal blotches; LB, the number of lateral blotches; ROWS, the height of lateral blotches measured in scale rows; and VEXT, the extent of ventral pigmentation) were analyzed. Patterns of natural selection were predicted from the relationship between color-pattern scores and independent measures of relative crypsis. Tests for natural selection were carried out using longitudinal data on neonate to juvenile-aged snakes and cross-sectional data on juvenile to adult-aged snakes. As predicted, the form of selection differed between younger and older age classes of snakes: selection resulted in a reduction in DB and LB among neonate and juvenile snakes but had little influence on color-pattern components in older snakes. The correspondence between observed patterns of natural selection and predictions based on the relationship between color-pattern scores and relative crypsis supports the hypothesis that differential predation by visual predators on younger age classes of snakes is the mechanism of selection. Gene flow from mainland populations or the initial lack of an allele necessary for reduced pattern may explain why selection has not resulted in greater differentiation between island and mainland populations.

Seasonal Reproduction in the African Olive Grass Snake, Psammophis phillipsi (Serpentes: Colubridae)

Forty-nine adult male, 30 adult female, and 46 unsexed juvenile olive grass snakes (Psam- mophis phillipsl) from Africa north of the equator were measured and dissected. Male snout-vent lengths were larger than those of females, and no dimorphism in tail length was found. Vitellogenesis commenced by the end of the rainy season, oviposition occurred by mid-dry season, and hatching occurred at the onset of the rainy season. Mean clutch size is 10.7 + 1.4 (n = 9, 6-19). No correlation between maternal snout- vent length and clutch size was detected. Testicular recrudescence began at the end of the rainy season, with regression beginning at the end of the dry season and continuing through the rainy season. Most hatchlings mature in the first year.

Morphology and ultrastructure of the venom glands of the northern pacific rattlesnake Crotalus viridis oreganus.

The venom gland of Crotalus viridis oreganus is composed of two discrete secretory regions: a small anterior portion, the accessory gland, and a much larger main gland. These two glands are joined by a short primary duct consisting of simple columnar secretory cells and basal horizontal cells. The main gland has at least four morphologically distinct cell types: secretory cells, the dominant cell of the gland, mitochondria-rich cells, horizontal cells, and "dark" cells. Scanning electron microscopy shows that the mitochondria-rich cells are recessed into pits of varying depth; these cells do not secrete. Horizontal cells may serve as secretory stem cells, and "dark" cells may be myoepithelial cells. The accessory gland contains at least six distinct cell types: mucosecretory cells with large mucous granules, mitochondria-rich cells with apical vesicles, mitochondria-rich cells with electron-dense secretory granules, mitochondria-rich cells with numerous cilia, horizontal cells, and "dark" cells. Mitochondria-rich cells with apical vesicles or cilia cover much of the apical surface of mucosecretory cells and these three cell types are found in the anterior distal tubules of the accessory gland. The posterior regions of the accessory gland lack mucosecretory cells and do not appear to secrete. Ciliated cells have not been noted previously in snake venom glands. Release of secretory products (venom) into the lumen of the main gland is by exocytosis of granules and by release of intact membrane-bound vesicles. Following venom extraction, main gland secretory and mitochondria-rich cells increase in height, and protein synthesis (as suggested by rough endoplasmic reticulum proliferation) increases dramatically. No new cell types or alterations in morphology were noted among glands taken from either adult or juvenile snakes, even though the venom of each is quite distinct. In general, the glands of C. v. oreganus share structural similarities with those of crotalids and viperids previously described.

Habitat Use by a Boid Snake, Epicrates monensis, and Its Anoline Prey, Anolis cristatellus

We quantified the habitat use of the endangered Virgin Islands boa (Epicrates monensis) and its prey (Anolis cristatellus) on Cayo Diablo, Puerto Rico. Although anoles occurred throughout the island, boas selectively foraged within groves of Coccoloba uvifera. Boas and anoles did not differ sig- nificantly in their plant species use within these groves. Adult male and adult female (>400 mm SVL) boas did not differ significantly for six measures of microhabitat use, but when juvenile snakes (s400 mm SVL) were included in the analysis, there was a significant correlation between boa SVL and foraging height. Adult male anoles occupied sleeping perches that were higher, of larger diameter, and farther out on branches than those of adult female and juvenile anoles. Principal components analysis revealed that anoles sleep on short, thin branches relative to those favored by foraging boas; adult male anoles occupy sleeping sites most similar in structure to those used by boas. We suggest that foraging by boas does affect habitat use of anoles, and that adult male anoles are constrained to sites similar to those used by boas by the need to hold territories or for high-quality thermal environments. Closed canopy woodland seems to be an important habitat requirement for the endangered E. monensis.

Stimulus control of antipredator behavior in newborn and juvenile garter snakes (Thamnophis).

Used neonate and juvenile garter snakes (Thamnophis sirtalis, T. melanogaster, and T. butleri) to investigate the role of visual stimuli in mediating antipredator behaviors and to examine the validity of techniques used to assess defensive responses

Venom Ontogeny in the Pacific Rattlesnakes Crotalus viridis helleri and C. v. oreganus

Ontogenetic variation in venom composition was examined in the Pacific rattlesnakes Crotalus viridis helleri and C. v. oreganus. Venoms were analyzed for protease, phospholipase A2, L-amino acid oxidase, exonuclease and elastinolytic activities, and toxicity toward a native prey (Sceloporus graciosus). Protease activity increased significantly with size; L-amino acid oxidase and exonuclease activities also tended to increase. Phospholipase A2 activity decreased significantly with size, as did venom toxicity. These factors produce a highly toxic venom with low protease activity in juvenile snakes, which facilitates efficient handling of lizards and young rodents. Analysis of gut contents of museum specimens showed that lizards constitute a major fraction of prey taken by juvenile rattlesnakes. Lizards continue to be taken with high frequency until snakes reach approx. 500 mm in total length; above this size, mammals are taken exclusively. As snakes increase in size, they feed on larger mammalian prey, and a functionally different venom is produced. Venom from adult Pacific rattlesnakes is less toxic but has high protease activity, aiding in the digestion of prey in a thermally variable environment.

Amount of venom injected by Russell's viper ( Vipera russelli)

Tun Pe and Khin Aung Cho. Amount of venom injected by Russell's viper ( Vipera russelli). Toxicon 24, 730 – 733, 1986.—The total yield of venom (desiccated) in 25 adult V. russelli (mean length 111 ± 1.8 cm (S.E.) ranges from 21 – 268 mg (127 ± 13 mg, mean ± S.E.) and that of 13 juvenile snakes (mean length 79 ± 2.8 cm) is 8 – 79 mg (45 ± 7 mg). The venom yield per milking correlated well with the length of the snake. The average amount of venom injected in the first bite of 31 adults (mean length 107 ± 1.4 cm) is 63 ± 7 mg (range 6 – 147 mg) and by 17 juvenile snakes (mean length 83 ± 1.1 cm) is 41 ± 8 mg (range 3 – 138 mg). Adults inject 45% of the glands' content in the first bite. More than 75 mg of venom (desiccated) was injected by 11 out of 31 adults and 2 out of 17 juvenile snakes. This indicates that in a substantial proportion of cases of envenomation, 40 ml of Burma Pharmaceutical Industry monovalent antivenom, which is commonly used, may not be adequate.

Foetal-Maternal Blood Respiratory Properties of an Ovoviviparous Snake the Cottonmouth, Agkistrodon piscivorus

ABSTRACT The respiratory properties of maternal, foetal and juvenile whole blood were studied in the ovoviviparous snake, Agkistrodon piscivorus. Haematocrit, haemoglobin concentration, O2 capacity, Bohr effect and Hill coefficients were not significantly different in foetal and maternal blood and were similar to values previously reported from snakes. A significant difference in foetal-maternal blood P50 (foetal 19·5, maternal 48·8) was found. Nucleoside triphosphate (NTP) levels were lower in foetal than in maternal and juvenile snakes. The foetal-maternal difference in P50 and NTP levels disappeared soon after birth (juvenile P50 45·5). Starch gel electrophoresis revealed no difference in foetal and maternal haemoglobins. We suggest that the foetal-maternal shift in blood oxygen affinity is modulated directly and/or indirectly by NTP levels.

Effects of Prey Size on Poststrike Behavior of Juvenile Red Spitting Cobras (Naja mossambica pallida)

Juvenile red spitting cobras (Naja mossambica pallida) held small neonatal mice (Mus musculus, 1.8-2.0 g) after striking but released larger mice (5.58.0 g). These results agree with data on viperids and suggest that N. m. pallida and perhaps other elapids will be found to exhibit strike-induced chemosensory searching and prey trailing behavior when relatively large rodents are attacked. Rattlesnakes typically strike and release adult rodent prey (Gans, 1966), permitting the envenomated rodent to wander up to 700 cm before succumbing to the venom (Estep et al., 1981). Small rodents, especially neonates, are often held in the snake's jaws after the strike, or they are sometimes swallowed without being struck (Radcliffe et al., 1980). Hence, poststrike trailing behavior occurs mainly when rattlesnakes attack relatively large rodent prey (Chiszar et al., 1977, 1978; Dullemeijer, 1961; O'Connell et al., 1981). Cobras also exhibit variability in poststrike behavior, although large specimens (including N. m. pallida) usually hold even adult mice (personal communication from M. Finstrom and K. Wintin, Knoxville Zoo, reptile dept.). Young cobras in particular seem to hold or release rodent prey depending upon prey size and/or defensive-struggling behavior. In fact, it has been hypothesized that the strike-release-trail strategy evolved as an adaptation by which juvenile venomous snakes deal with relatively large and formidable This content downloaded from 207.46.13.124 on Wed, 22 Jun 2016 05:27:59 UTC All use subject to http://about.jstor.org/terms 60 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE rodent prey (Chiszar et al., 1982). Hence, the present study was designed to determine if juvenile cobras hold or release rodents as a function of prey weight.

Quatic Foraging in Garter Snakes: a Comparison of Specialists and Generalists

AbstractTo examine the assumption, underlying much ecological theory, that a "Jack-of-all-trades is master of none", a comparison was made of the aquatic predation of four colubrid snakes, two aquatic specialists (Thamnophis couchi, T. melanogaster) and two terrestrial-aquatic generalists (T. sirtalis, and T. elegans). Observations were made in the field, then juvenile snakes were compared under controlled laboratory conditions. The specialists and generalists had qualitatively different foraging repertoires. The specialists made lengthy dives, crawled slowly on the underwater substrate and made long-distance underwater responses to prey: orientation, approach, pursuit, and frontal attack. The generalists dived briefly, with rapid serpentine locomotion, or searched "terrestrially" by wandering along the shoreline and snatching prey from the water surface. Underwater, the generalists' only prey-directed response was sudden short-distance attack, and they appeared to rely on chance encounters with prey. There were significant differences between the two pairs. In comparison with the generalists, the specialists 1) captured more fish, 2) spent more time on aquatic search, 3) spent more aquatic search time diving, 4) spent more diving time on the underwater substrate, 5) made more attacks in every category of search in open water, and 6) attacked underwater from a greater distance. Significant differences were not found in attack frequencies in those search categories where underwater vision is probably unimportant (aerial attacks and attacks in underwater crevices), nor in aerial attack distances. The specialists' behavioral superiority in respect of their specialization supports the "Jack-of-all-trades" assumption. The observations suggest that this superiority is associated with superior underwater visual acuity (which may be due to superior visual accommodation). The generalists' principal underwater searching technique (serpentine diving) appears to be energetically costly, and may only be profitable when aquatic prey are especially vulnerable. Nerodia sipedon, member of a genus that is closely related to Thamnophis but more aquatic, had a foraging repertoire qualitatively similar to that of the generalists. The similarity may be associated with N. sipedon's nocturnal habits and presumed reliance on non-visual prey cues.

Ontogenetic change in blood oxygen capacity and maximum activity in garter snakes (Thamnophis sirtalis)

There is an ontogenetic increase in the time that garter snakes (Thamnophis s. sirtalis) can maintain maximum activity at 25°C. Newborn snakes are exhausted by 3–5 min of activity while adults can be active for 20–25 min. The increased endurance of adult snakes results from ontogenetic increases in both aerobic and anaerobic energy generation. At rest juvenile and adult snakes have the same whole-body lactic acid concentrations, but at exhaustion adult lactic acid concentrations are 1.5 times those of juveniles. This increase in anaerobic energy production accounts for part of the endurance of adult snakes, but increased aerobic metabolism appears to be more important. Among the mechanisms increasing aerobic metabolism are more effective pulmonary ventilation and a 3-fold ontogenetic increase in blood oxygen capacity. The rapid exhaustion of small garter snakes probably limits the microhabitats they can occupy and the sorts of hunting methods they can employ. Small garter snakes feed only on small prey that are easily subdued. There is an ontogenetic increase in the relative size of prey eaten by garter snakes that parallels the ontogenetic increase in endurance. Adult feeding habits are adopted at the same body size at which adult blood oxygen capacity and endurance are attained.

Observations on toxicity and antigenic makeup of venoms from juvenile snakes

Observations on toxicity and antigenic makeup of venoms from juvenile snakes

Further Notes on Differential Selection of Variant Juvenile Snakes

Further Notes on Differential Selection of Variant Juvenile Snakes

Differential Selection of Variant Juvenile Snakes

Differential Selection of Variant Juvenile Snakes