The role of temperature in microhabitat selection by northern water snakes (Nerodia sipedon)

1992 ◽  
Vol 70 (3) ◽  
pp. 417-422 ◽  
Author(s):  
Ian C. Robertson ◽  
Patrick J. Weatherhead
Keyword(s):  
Experimental Manipulation ◽  
Time Of Day ◽  
Microhabitat Selection ◽  
Nerodia Sipedon ◽  
Leopard Frogs ◽  
Water Snake ◽  
Northern Water Snakes ◽  
Water Snakes ◽  
Circadian Patterns

Using field observations and laboratory experiments we examined the role of temperature in microhabitat selection by an eastern Ontario population of northern water snakes (Nerodia sipedon). From 1349 random transects through a marsh we found that basking activity peaked at 09:00 and then declined steadily until 14:00 before increasing again. Our ability to detect snakes depended upon the microhabitat they occupied, and to the time of day when the snakes were encountered in water. In the field, temperatures of basking snakes averaged (±SE) 26.3 ± 0.7 °C (n = 36), while captive snakes in a thermal gradient showed a narrower selectivity, averaging 27.7 ± 0.4 °C (n = 21). The temperatures of basking snakes never exceeded 33 °C, even though a model snake placed in the sun reached 48 °C, suggesting that the snakes were thermoregulating to prevent overheating. In both the field and enclosures, water snakes basked more frequently as the temperature of the air increased relative to the water. Experimental manipulation of water temperature relative to air temperature revealed that temperature influenced microhabitat selection independently of circadian patterns. Finally, when in water, snakes tended to frequent habitats where leopard frogs (Rana pipiens), a common prey species, were most abundant, suggesting that prey distribution may also be an important component of water snake habitat selection.

Variation in offspring sex ratios in the northern water snake (Nerodia sipedon)

1998 ◽  
Vol 76 (12) ◽  
pp. 2200-2206 ◽  
Author(s):  
Patrick J Weatherhead ◽  
Gregory P Brown ◽  
Melanie R Prosser ◽  
Kelley J Kissner
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Birth Date ◽  
Nerodia Sipedon ◽  
Water Snake ◽  
In Captivity ◽  
Northern Water Snake ◽  
Northern Water Snakes ◽  
Gravid Females ◽  
Water Snakes

We used data from 88 litters of northern water snakes (Nerodia sipedon) to test predictions about how mothers would adaptively vary the sex ratios of their offspring. Larger mothers produced significantly more daughters (r2 = 0.04, P = 0.05), and mothers producing larger offspring produced significantly more daughters (r2 = 0.06, P = 0.02). Because neonate size did not vary with maternal size, these sex-ratio patterns were independent of each other. These patterns were more pronounced for wild females than for females maintained in captivity while gravid, but rearing conditions did not have a significant effect on sex ratio. Also, because sex ratios were similar between captive and free-living females despite captive females giving birth 16 days earlier, on average, and because sex ratios did not vary with birth date within the two groups of females, gestation appeared not to affect sex ratio. If females vary sex ratios adaptively, only the relationship between sex ratio and neonate size was consistent with our predictions. Limited evidence from other snake species also indicates variation in neonatal sex ratios that is nonrandom but not necessarily adaptive. A better understanding of these patterns will require information on the factors that affect the fitness of male and female neonates differently. An unexpected sex-ratio pattern that we found was that 14 of 19 stillborn young were male. We speculate that this pattern could be a result of male embryonic sensitivity to temperature. Thus, the need for gravid females to maintain a high body temperature so that their young are born with enough time to find hibernation sites may conflict with the need for embryos to develop at a safe temperature.

Thermal constraints on swimming performance and escape response of northern water snakes (Nerodia sipedon)

1992 ◽  
Vol 70 (1) ◽  
pp. 94-98 ◽  
Author(s):  
Patrick J. Weatherhead ◽  
Ian C. Robertson
Keyword(s):  
Body Temperature ◽  
Water Temperature ◽  
Swimming Speed ◽  
Escape Response ◽  
Swimming Performance ◽  
Nerodia Sipedon ◽  
Water Snake ◽  
Northern Water Snakes ◽  
The Cost ◽  
Water Snakes

We examined the influence of body temperature on swimming speed of northern water snakes (Nerodia sipedon) and determined how variation in water temperature influenced their escape response. In a laboratory experiment, swimming speed increased as a function of water temperature and body size. Swimming speed was less thermally dependent at temperatures approximating the snakes' normal range of activity, suggesting that selection has favoured increased performance breadth at this range. In the field, basking snakes retreated to water when approached. Despite a decrease in swimming speed at lower temperatures, and the cost associated with reduced metabolic rate due to loss of body temperature, however, flight distances were independent of water temperature. We found that basking snakes retreated to water sooner when perched at lower heights, possibly indicating that N. sipedon are more vulnerable to predators when on low perches. Predicting water snake escape behaviour may require not only knowledge of variation both among snakes and in their environment, but also a better understanding of the interaction between the snakes and their natural predators.

Demography and sexual size dimorphism in northern water snakes, Nerodia sipedon

1999 ◽  
Vol 77 (9) ◽  
pp. 1358-1366 ◽  
Author(s):  
Gregory P Brown ◽  
Patrick J Weatherhead
Keyword(s):  
Sexual Maturity ◽  
Sexual Size Dimorphism ◽  
Survival Rates ◽  
Seasonal Patterns ◽  
Nerodia Sipedon ◽  
Size Dimorphism ◽  
Mortality Cost ◽  
Northern Water Snakes ◽  
Water Snakes ◽  
Better Than

We used data from a 9-year mark-recapture study to determine whether demographic factors could explain female-biased sexual size dimorphism in northern water snakes (Nerodia sipedon). Most males reached sexual maturity at 3 years of age, while most females delayed maturity for an additional year. Female survivorship was not significantly lower than that of males, despite the fact that females grow as much as four times faster than males. Among females, survivorship increased until maturity and decreased thereafter, suggesting a survival cost to reproduction. Life-table calculations indicated that the increase in both survival rates and fecundity with body size made 3 years the optimal age for females to reach sexual maturity. However, if females were not large enough at 3 years of age, their best strategy was to mature the following year. Seasonal patterns of mortality suggest that mating imposes a high mortality cost on males. Intermediate-sized males survived slightly but not significantly better than small and large males. This slight survival advantage of intermediate-sized males was not sufficient to explain why males are so much smaller than females. Therefore other selective factors must be responsible for males retaining a small size. A reproductive advantage associated with small size seems the most likely possibility.

Life cycles, morphological characteristics, and host specificity of Hepatozoon species infecting eastern garter snakes from Ontario

1996 ◽  
Vol 74 (10) ◽  
pp. 1850-1856 ◽  
Author(s):  
Todd G. Smith ◽  
Susan H. Kopko ◽  
Sherwin S. Desser
Keyword(s):  
Morphological Characteristics ◽  
Life Cycles ◽  
Thamnophis Sirtalis ◽  
Garter Snakes ◽  
Leopard Frogs ◽  
Northern Water Snakes ◽  
Vertebrate Hosts ◽  
Hepatozoon Species ◽  
Northern Leopard Frogs ◽  
Water Snakes

The life cycles of species of Hepatozoon that occur naturally in eastern garter snakes, Thamnophis sirtalis sirtalis, were studied in the mosquito Culex pipiens in various amphibians, including northern leopard frogs, bullfrogs, gray treefrogs, American toads, and blue-spotted salamanders, and in natricine snakes, including northern water snakes and northern brown snakes. Morphological features of the oocysts of two forms of Hepatozoon from various widely separated regions of Ontario differed with respect to the number of sporozoites per sporocyst and the diameter and shape of the oocyst. However, morphological and morphometric differences were not apparent in the cystic or merogonic stages in the vertebrate hosts. Cystic stages of these haemogregarines were found in the liver of all four species of anurans, but not in salamanders. These forms were transmitted experimentally to garter, water, and brown snakes, with gamonts appearing in erythrocytes 45 days after the snakes were fed infected anurans. A comparison of these forms of Hepatozoon with previously named species of ophidian haemogregarines from North America indicates that there are at least two, and likely more, species of Hepatozoon in Ontario.

Growth and Sexual Size Dimorphism in Northern Water Snakes (Nerodia sipedon)

Copeia ◽  
1999 ◽  
Vol 1999 (3) ◽  
pp. 723 ◽  
Author(s):  
Gregory P. Brown ◽  
Patrick J. Weatherhead
Keyword(s):  
Sexual Size Dimorphism ◽  
Nerodia Sipedon ◽  
Size Dimorphism ◽  
Northern Water Snakes ◽  
Water Snakes

Multiple paternity in a wild population of northern water snakes, Nerodia sipedon

1992 ◽  
Vol 30 (3-4) ◽  
pp. 193-199 ◽  
Author(s):  
Frances E. Barry ◽  
Patrick J. Weatherhead ◽  
David P. Philipp
Keyword(s):  
Wild Population ◽  
Multiple Paternity ◽  
Nerodia Sipedon ◽  
Northern Water Snakes ◽  
Water Snakes

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

2002 ◽  
Vol 23 (3) ◽  
pp. 333-342 ◽  
Author(s):  
John Himes
Keyword(s):  
Kin Recognition ◽  
Activity Patterns ◽  
Prey Type ◽  
Size Class ◽  
Prey Fish ◽  
Nerodia Sipedon ◽  
Foraging Mode ◽  
Water Snake ◽  
Predator Foraging

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.

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