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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.

In: Behaviour

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.

In: Behaviour

Abstract

The purpose of this experiment was to test the hypothesis that the disruptive acts (nest raiding), directed by male three-spined sticklebacks, Gasterosteus aculeatus L., toward the eggs and nests of conspecific males evolved as a result of intrasexual selection. We compared the frequency with which a resident male was raided by neighbors when a transparent cylinder containing a male was introduced into his territory, with the frequency of raiding during the presence of a similarly introduced female. On the basis of the intrasexual selection hypothesis, we predicted that raiding should occur more often when the female was present. We also studied the relationship between raiding and the relative dominance status of raided and raiding males. If raiding and dominance conflict are alternative strategies in intrasexual competition, then raiding should have been most intense when raided and raiding males were least discrepant in dominance status. Resident males responded appropriately to introduced fish, i.e., with more courtship and nesting behavior toward females and more aggression toward males. Introduced females were much more effective in eliciting raiding by neighbors than introduced males. The highest status neighbors tended to raid the most. There was some evidence that raiding reduced the raided male's courtship motivation. The outcome of the study is compatible with the hypothesis that nest raiding is adaptive because it increases the relative attractiveness of the raider to females.

In: Behaviour

Abstract

Arctic ground squirrels (Spermophilus parryii ablusus) have been free from snake predation for about 3 million years. To evaluate the effects of this prolonged relaxation of natural selection, lab-born Arctic ground squirrels were compared to snake-inexperienced California ground squirrels (Spermophilus beecheyi fisheri) from a habitat where rattlesnake and gopher snake predation is intense. Their behavior was video taped during 10-min encounters with a Pacific gopher snake (Pituophis melanoleucus catenifer) in a seminatural above-ground setting and in an artificial burrow. In separate trials, a domesticated Norway rat was used as a control for the effects of encountering a novel animate object; this rat was enclosed in a slowly moving opaque nylon bag above ground but was allowed to move freely below ground. No evidence was found that, after prolonged relaxed selection from snakes, Arctic ground squirrels retained the specialized behavioral antisnake defenses evident in California ground squirrels. Although we originally hypothesized that the more constrained burrow context might limit the evolutionary dissipation of behavioral antisnake defenses, we found no evidence of a more intact system in Arctic squirrels below than above ground. Arctic squirrels used many of the same general kinds of motor patterns as California squirrels, but in ways that failed to differentiate the gopher snake from the rat in either above- or below-ground contexts. In contrast, the California squirrels tail flagged only in the presence of the snake above ground and differentially applied substrate-throwing at the snake and rat burrow intruders, harassing the snake more than twice as much as the rat. Above ground, California ground squirrels were more conservative toward both adversaries than Arctic ground squirrels were, keeping their distance and therefore experiencing fewer noxious consequences, such as snake strikes. However, this result was context dependent. Below ground, California ground squirrels were more willing than Arctic ground squirrels to approach and harass both burrow intruders. Although repeated striking evoked occasional snake-directed substrate throwing above ground, Arctic ground squirrels never threw substrate at the snake in the burrow. In comparison with California ground squirrels, Arctic ground squirrels appear to enter their first gopher snake encounter with both a much lower assessment of the risk involved and less clearly defined knowledge about how to deal with these risks. We conclude that 3 million years of genetic drift has altered the cognitive system structuring the meaning of snakes to Arctic ground squirrels in various settings.

In: Behaviour

Abstract

The predator-evoked calling of California ground squirrels (Spermophilus beecheyi) was studied in the field during the reproductive season. Three different sources of data indicated that adults call more after, than before their young have reached the age of first emergence from natal burrows. During exposure to a tethered rattlesnake (Crotalus viridis oreganus) and to a freely-moving dog (Canis familiaris), and in natural encounters with a coyote (Canis latrans) or bobcat (Lynx rufus), calling was more frequent after than before young first emerged. We concluded that California ground squirrels call in order to warn their offspring about predators, like other ground squirrel species do. In order to see the increase in mammalian predator evoked calling after pup emergence, we had to separate calling on the basis of its temporal organization. Nonrepetitive calling involved spacing a few vocalizations irregularly in time. Calls patterned in this way were more common early in an encounter, became more frequent after pup emergence, and more consistently elicited immediate reactions. Such calling was probably used to warn pups. Repetitive calling comprised rhythmic emission of a series of vocalizations. Calls organized repetitively were more common later in an encounter, were not emitted more frequently after pup emergence, and less consistently evoked immediate reactions. These and other differences between the two temporal patterns of vocalizing led us to propose that repetitive calling represented a "tonic" communicatory effort (as in SCHLEIDT, 1973). Repetitive inputs to other squirrels may act "cumulatively" in a longer time scale than nonrepetitive calling, so as to cultivate or maintain vigilance in other squirrels. The repetitive caller could benefit by using the enhanced reactions of these more vigilant squirrels as a source of information about the predator. We propose that predator-prey episodes may be understandable from an "epigenetic" perspective. That is, the first alarm calls during an encounter should shift squirrels from an unwarned to a warned status; subsequent calling must then function in some other way than as a warning.

In: Behaviour

Abstract

In this paper we report the results of our first efforts to evaluate the functional significance to signaler and perceiver of variation in tail flagging (Fig. 1 and Fig. 2A-C) by California ground squirrels (Spermophilus beecheyi). We first report a series of anecdotes in which we describe the circumstances of a variety of tail movements by California ground squirrels, including the different kinds of tail flagging. Secondly and primarily we identify the information afforded by snake-elicited tail flagging. Tail flagging is a signal used by California ground squirrels primarily when they are harassing a potential snake predator (Fig. 4). It attracts other squirrels who may also begin harassing the snake. The risk to squirrels in encounters with snakes continuously varies, and the squirrels adjust their behavior accordingly. Consequently in this situation we expected to find shifts in the information afforded by different tail-flagging variants. We view the information afforded by tail movement and other signals as a consequence, not of selection for making that information available, but of the correlations resulting from situational constraints on the signaler's behavior, e.g., correlations between tail movement variation and variation in significant events. We used two complementary approaches to help determine the information afforded by tail flagging. In one, we asked whether information important to percipients is afforded by tail flagging. In the second, we searched for situational correlates of tail-flagging variants. We applied the second approach to each individual separately and to the group comprising these individuals. This allowed us to look for idiosyncrasies in signaler behavior. Although a relatively simple signal, tail flagging varies along several structural and temporal parameters. From video recordings we quantified a structural parameter- number of movement cycles in a bout of tail flagging - and two temporal parameters- rate and temporal clustering of tail flagging. Our results show that squirrels adjust their tail-flagging behavior in the following ways. 1. When a rattlesnake rattles, harassing squirrels increase the number of cycles per bout of tail flagging. 2. Lone snake-directed squirrels temporally clump their flagging bouts more than snake-directed squirrels accompanied by other snake-directed individuals. 3. The structure of flagging varied with the squirrel's behavior vis-a-vis the snake. While dealing directly with a snake, squirrels emitted relatively few 1-cycle bouts of flagging. While in the vicinity and monitoring snake-related events, but engaged primarily in other activities such as feeding or grooming, squirrels emitted relatively greater numbers of 1-cycle bouts. As one would predict from this difference, individuals were farther from the snake on the average while emitting 1-cycle bouts than while emitting 2-cycle bouts. Adults used far more 2-cycle bouts than 1, and 3 or higher. In the field, bouts of 4-cycles or greater were very rare. We found that the information afforded by a bout of tail flagging was much greater when we considered structural variation, than when we did not. For example, flaggers were more likely on the average to "pause" before than after tail flagging. However, although the same difference held for 1-cycle bouts, just the reverse was true for 3-cycle bouts, and there was little difference in the probability of pausing for 2-cycle bouts. We found similar differences for other behavioral correlates of tail flagging. A percipient could much more precisely predict a tail flagger's behavior by considering signal variation. Our results indicate a percipient can infer from a high proportion of 3-cycle bouts that the flagger is beginning an episode of snake-directed activity, whereas 1-cycle bouts indicate a temporary cessation of snake-directed behavior. We expect to find even greater situational specificity of tail flagging when we simultaneously consider multiple structural dimensions, such as axis of movement and number of cycles. When we looked at the information afforded by a bout of tail flagging separately for individual squirrels, it was clear that the specific behavioral profiles associated with different variants of tail flagging were somewhat idiosyncratic. Thus, a percipient squirrel should be able to infer more from the tail flags of a familiar squirrel than an unfamiliar squirrel. We propose that signals are used to elicit a particular kind of performance from the target(s). The effectiveness of such action depends upon a knowledge of the current status of the individual's target(s). We conclude that variation in tail flagging is constrained in at least three ways: 1) by the number and quality of targets of tail flagging (e.g., snakes, squirrels); 2) by the signaler's certainty about the status of the target(s) (by eliciting behavior in targets, tail flagging may be used in part to extract information about the target's state); and 3) by the quality and availability of feedback (the success of tail flagging is continually assessed on the basis of feedback). The understanding of the functional significance of tail flag variability therefore becomes the problem of understanding how the flagger uses signal adjustments to deal with changes in its circumstances in terms of these three general constraints.

In: Behaviour