SNAKE-DIRECTED ANTIPREDATOR BEHAVIOR OF ROCK SQUIRRELS (SPERMOPHILUS VARIEGATUS): POPULATION DIFFERENCES AND SNAKE-SPECIES DISCRIMINATION

Behaviour ◽  
2001 ◽  
Vol 138 (5) ◽  
pp. 575-595 ◽  
Author(s):  
Matthew Rowe ◽  
Donald Owings ◽  
Diane McKernon ◽  
Patricia Arrowood ◽  
Richard Coss
Keyword(s):  
Sexual Size Dimorphism ◽  
Antipredator Behavior ◽  
Ground Squirrels ◽  
Urban Site ◽  
Species Discrimination ◽  
Population Differences ◽  
Behavioral Differences ◽  
Size Dimorphism ◽  
Study Sites ◽  
California Ground Squirrels

AbstractThe purposes of this study were: (1) to describe the snake-directed antipredator behavior of rock squirrels; (2) to assess whether rock squirrels distinguish nonvenomous gopher snakes from venomous rattlesnakes; (3) to compare antisnake behavior in a snake-rare urban site and a snake-abundant wilderness site as a means of assessing whether natural selection or experience has generated population differences in behavior; (4) to assess snake densities in the two study sites; (5) to compare the antisnake behavior of rock squirrels with that of their closest relatives, California ground squirrels (Spermophilus beecheyi), a species that appears to differ from rock squirrels in exhibiting marked sexual-size dimorphism; and (6) to gather additional data on sexual size dimorphism in these two ground squirrel species. We tethered nonvenomous gopher snakes (Pituophis melanoleucus) and venomous western diamondback rattlesnakes (Crotalus atrox) in the field near burrows of marked squirrels and videotaped the ensuing interactions. Rock squirrels from both urban and wilderness populations confronted snakes while waving their fluffed tails from side to side, throwing substrate at the snakes, and even attacking snakes on occasion. Survey data confirmed large differences in snake densities between the two sites. Squirrels from the snake-abundant wilderness site distinguished rattlesnakes from gopher snakes, but squirrels from the snake-rare urban site did not. Since these squirrels show similar evidence of selection from snakes, as revealed by their equivalent physiological resistance to rattlesnake venom, we attributed these behavioral differences to the effects of snake experience. Rock squirrel antisnake behavior was very similar to that of California ground squirrels. Where the two species' behavior was dissimilar, the differences may be due in part to the interspecies variation in sexual size dimorphism confirmed in this study, and to the greater number of rattlesnake species that rock squirrels encounter.

Development of Antisnake Defenses in California Ground Squirrels (Spermophilus Beecheyi): II. Microevolutionary Effects of Relaxed Selection From Rattlesnakes

Behaviour ◽  
1993 ◽  
Vol 124 (1-2) ◽  
pp. 137-162 ◽  
Author(s):  
Richard G. Coss ◽  
Naomie S. Poran ◽  
Kevin L. Gusé ◽  
David G. Smith
Keyword(s):  
Population Level ◽  
Ground Squirrels ◽  
Species Discrimination ◽  
Spermophilus Beecheyi ◽  
Relaxed Selection ◽  
Virtual Absence ◽  
Rare Site ◽  
California Ground Squirrels ◽  
Two Populations

AbstractNonvenomous Pacific gopher snakes (Pituophis melanoleucus catenifer) and venomous northern Pacific rattlesnakes (Crotalus viridis oreganus) have coexisted in a predator-prey relationship with California ground squirrels (Spermophilus beecheyi) for many thousands of generations. This long-term relationship has fostered in ground squirrels the evolution of antisnake defenses that consist of physiological resistance to rattlesnake venom and behavioral tactics of probing and harassing that might facilitate snake-species discrimination. Snake harassment by adults might also protect pups by interfering with snake hunting activities. Some ground squirrel populations have colonized habitats where rattlesnakes, but not gopher snakes, are rare or absent. Initial research indicates that squirrels experiencing relaxed selection from rattlesnakes are very aggressive toward their remaining nonvenomous snake predator, the gopher snake. Two experiments investigated the effects of relaxed selection from rattlesnakes by examining: 1) changes in level of venom resistance, 2) the reorganization of antisnake behaviors in lab-born pups and wild-caught adults from different sites, and 3) the role of natural experiences on the development of antisnake behavior in a rattlesnake-adapted population. Level of venom resistance was examined by an in vitro radioimmunoassay of serum-to-venom binding of two populations of Douglas ground squirrels (S. b. douglasii). The ancestors of one population are estimated to have experienced relaxed selection from rattlesnakes for about 9,000 years based on genetic distance and radiocarbon analyses. The antisnake behavior of 60-73 day-old lab-born pups from these two populations was video taped during presentations of a caged rattlesnake or gophcr snake for alternate 5-min trials in a seminatural laboratory setting. Two groups of wild-caught adult Beechey groundsquirrels (S. b. beecheyi) were studied using the same protocol for examining antisnake behavior. One group was obtained from a population that recently colonized a rattlesnake-rare site and exhibits moderate venom resistance. The second group came from a population that exhibits very low venom resistance and inhabits a rattlesnake-free site; relaxed selection from rattlesnakes for this population is estimated to span approximately 60,000 years. Comparisons of Douglas ground squirrels from rattlesnake-abundant and rettlesnakerare sites revealed that venom resistance declined approximately 59% after an estimated 9,000 years of relaxed selection from rattlesnakes. Lab-born Douglas pups from the same rattlesnake-rare site were more aggressive toward the gopher snake than toward the rattlesnake whereas pups from the population experiencing predation from both species of snake treated both snakes as similarly dangerous. Unlike pups, wild-caught adults from the rattesnake-adapted population harassed the rattlesnake more intensely than the gopher snake, a phenomenon that may reflect their experience with snakes in nature and larger body size that reduces their vulnerability to envenomation. Wild-caught Beechey ground squirrels that recently colonized a rattlesnake-rare site did not differentiate the rattlesnake and gopher snake whereas Beechey ground squirrels whose ancestors have experienced prolonged relaxed selection from rattlesnakes were more aggressive toward the gopher snake. Consistent with previous findings, prolonged relaxed selection from rattlesnakes, but not gopher snakes, appears to have reduced the inhibition to harass large gopher snakes. This microevolutionary shift in increased aggressiveness toward the gopher snake could result from the virtual absence of any risk in misidentifying rattlesnakes from gopher snakes.

Snake Species Discrimination and the Role of Olfactory Cues in the Snake-Directed Behavior of the California Ground Squirrel

Behaviour ◽  
1978 ◽  
Vol 65 (1-2) ◽  
pp. 115-123 ◽  
Author(s):  
Hennessy David F. ◽  
Owings Donald H.
Keyword(s):  
Visual Cues ◽  
Ground Squirrels ◽  
Species Discrimination ◽  
Transparent Plastic ◽  
California Ground Squirrel ◽  
Snake Species ◽  
Crotalus Viridis ◽  
Plastic Bags ◽  
California Ground Squirrels

This experiment had two objectives. One was to seek evidence for greater caution by California ground squirrels (Spermophilus beccheyi) when interacting with venonnous rattlesnakes (Crotalus viridis), their most important snake predator, than when interacting with nonvenomous gopher snakes (Pituophis melanoleucus), their second-most important snake predator. The second was to examine the role of olfaction in mediating snake-directed behavior by these squirrels, since matry squirrel-snake encounters occur in burrows where visual cues are unavailable. In an illuminated room, we videotaped the responses by eight freely moving ground squirrels to the two snake species; the snakes were presented in large, transparent plastic bags that were either sealed (odor unavailable) or perforated (odor available). The results confirmed our predictions that the squirrels should behave more cautiously toward rattlesnakes than toward gopher snakes, and that olfaction is an important mediator of snake-directed behavior. Although the squirrels approached the two snake species equally often, they attended more to the rattlesnake than to the gopher snake, but remained farther away from the rattlesnake. When snake odor was available, the squirrels spent more time attending to the snakes, approached the snakes more frequently, approached the snakes in elongate postures more often and sand kicked more at the snakes. We proposed the following. 1. The antipredator strategy of snake harassment by California ground squirrels is sensitive to risk, exhibiting attenuation where risk is higher. 2. Olfaction is likely to be even more important during squirrel-snake encounters in the dark, especially in burrows. 3. The ability to recognize snakes on the basis of odor may not depend on prior experience with snakes, and may circumvent difficulties associated with visual detection of snakes.

Snake Species Discrimination and the Role of Olfactory Cues in the Snake-Directed Behavior of the California Ground Squirrel

Behaviour ◽  
1978 ◽  
Vol 65 (1-2) ◽  
pp. 115-123 ◽  
Author(s):  
Hennessy David F. ◽  
Owings Donald H.
Keyword(s):  
Visual Cues ◽  
Ground Squirrels ◽  
Species Discrimination ◽  
Transparent Plastic ◽  
California Ground Squirrel ◽  
Snake Species ◽  
Crotalus Viridis ◽  
Plastic Bags ◽  
California Ground Squirrels

This experiment had two objectives. One was to seek evidence for greater caution by California ground squirrels (Spermophilus beccheyi) when interacting with venomous rattlesnakes (Crotalus viridis), their most important snake predator, than when interacting with nonvenomous gopher snakes (Pituophis nielanoleucus), their second-most important snake predator. The second was to examine the role of olfaction in mediating snake-directed behavior by these squirrels, since many squirrel-snake encounters occur in burrows where visual cues are unavailable. In an illuminated room, we videotaped the responses by eight freely moving ground squirrels to the two snake species; the snakes were presented in large, transparent plastic bags that were either sealed (odor unavailable) or perforated (odor available). The results confirmed our predictions that the squirrels should behave more cautiously toward rattlesnakes than toward gopher snakes, and that olfaction is an important mediator of snake-directed behavior. Although the squirrels approached the two snake species equally often, they attended more to the rattlesnake than to the gopher snake, but remained farther away from the rattlesnake. When snake odor was available, the squirrels spent more time attending to the snakes, approached the snakes more frequently, approached the snakes in elongate postures more often and sand kicked more at the snakes. We proposed the following. i. The antipredator strategy of snake harassment by California ground squirrels is sensitive to risk, exhibiting attenuation where risk is higher. 2. Olfaction is likely to be even more important during squirrel-snake encounters in the dark, especially in burrows. 3. The ability to recognize snakes on the basis of odor may not depend on prior experience with snakes, and may circumvent difficulties associated with visual detection of snakes.

Morphology and diet of two sympatric colubrid snakes, Chironius flavolineatus and Chironius quadricarinatus (Serpentes: Colubridae)

2008 ◽  
Vol 29 (2) ◽  
pp. 149-160 ◽  
Author(s):  
Otavio Augusto Vuolo Marques ◽  
Ronaldo Fernandes ◽  
Roberta Richard Pinto
Keyword(s):  
Foraging Behaviour ◽  
Sexual Size Dimorphism ◽  
Sympatric Species ◽  
Colour Pattern ◽  
Ontogenetic Variation ◽  
Brazilian Cerrado ◽  
Size Dimorphism ◽  
Snake Species ◽  
Dietary Ecology ◽  
Arboreal Habit

Abstract The morphometry and diet of two sympatric species of Chironius (C. flavolineatus and C. quadricarinatus) from Brazilian Cerrado are described. The two snake species differ in external morphology, as Chironius flavolineatus was the largest species (body, tail and eyes) whereas C. quadricarinatus the heaviest. Each species also showed marked sexual size dimorphism. In terms of dietary ecology, both species feed exclusively on frogs with a heavy preference for hylids and may have tendency to eat small items, as noticed in other colubrine species. These two snake species showed a brownish colour pattern and exhibited no ontogenetic variation, suggesting that juveniles and adults use similar substrates. Chironius flavolineatus and C. quadricarinatus present a semi-arboreal habit, with active foraging behaviour, feeding in the ground most of time. Chironius flavolineatus uses higher vegetation for resting and, based on morphological results, seems to be more arboreal than C. quadricarinatus.

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