Predator odors avoidance

This first of two experiments on predator odor avoidance deals with nocturnal burrowing mammals. The second will involve day-active mammals, such as squirrels (see Chap. 5). 

An example for stimulus generalization are responses of rats to stress-inducing odors. Laboratoiy rats of the Wistar strain respond to predator odors, specifically mercapto compounds in fox droppings, with stress reactions, for example avoidance behavior such as freezing and increased plasma corticosterone concentrations (Vemet-Mauiy et ah, 1984). The rats were trained to avoid water scented with a mercapto odorant that contained both a keto- and a sulfhydryl group (4-mercapto-4-methyl-2-pentanone). As the animals licked a waterspout, a mild electric shock was applied to their tongue. When different compounds were tested thereafter, the rats avoided compounds with similar... 

In Australia, house mice living on islands without predators did not avoid traps treated with predator odors. In areas where the introduced red fox or house cat occur, or the native western quoll, Dasyurusgeoffroyii, the mice avoided... 

Laboratory and domestic animals may be poor models for avoidance of predator odors. For example, in one experiment, chickpeas were painted with the sulfur compounds w-propyldithiolane and w-propylthiolane from stoat anal gland secretion and 2,4,5-trimethylthiazoline (Fig. 3.1, p. 37) from fox feces. The chickpeas were planted and wild mice and house mice were tested to see if they would dig up and eat the peas. Wild mice remembered the predator odors better after odor exposure for 1 or 4 weeks and, consequently, may be better than laboratory mice at risk assessment (Coulston etal, 1993). 

We will examine whether the small mammals vulnerable to predation will avoid fresh predator odors in their home ranges. For this purpose we place in the woods live traps that are scented with odors from red fox and wolf. This experiment teaches not only basic ecology, but also the very practical skill how to test potential chemical repellents for rodent pests. 

We will examine whether a diurnal rodent, the gray squirrel (Sciurus carolinensis) avoids predator odors and whether this avoidance is specific to certain predator species that pose more of a threat than others. This experiment arose from our course Chemical Ecology of Vertebrates during the autumn of 2000. Surprisingly, we could not find published studies of predator odor effects on squirrels. Dr. Frank Resell, then a student in the course, undertook this experiment as his individual research project and extended it after the end of the course for a publication (Rosell 2001). 

The predator scents typically used in experiments are urine, extracts of feces, scent gland products, or combinations of these. Behavioral responses of small mammal to predator odor stimuli range from vigilance to avoiding the site, and feeding inhibition. We can test squirrels responses to odors of an arboreal predator (cat), a ground predator (fox), and to humans (in most areas harmless pedestrians, but in others they are squirrel hunters), and compare them with their behavior toward odors of a nondangerous herbivore, such as deer or cattle. 

Because the odor of cat urine was not known to our animals before the experimental exposure, one could assume that the response to the predator urine odor has a strong innate basis. This suggestion corresponds with some observations showing that the avoidance reaction to predator odors is innate rather than learned (Miiller-Schwarze, 1972 Gorman, 1984 Merkens, Harestad Sullivan, 1991 Caldera Gorman, 1991 Epple, Maison, Nolte Campbell, 1993 Heth Todrank, 1995 Sullivan et al., 1988a, b). 

Three major explanations have been given for the avoidance response we observed in red-backed salamanders the avoidance of predator odors (Roudebush Taylor, 1987 Brodie, et al., 1991), the avoidance of interspecific competitor odors (Ducey, et al., 1994),... 

Small rodents depend on detection of a predator prior to actual contact. Thus, voles are sensitive to the scent of potential predators and respond to such odors without the necessity for other cues. In the wild, field voles Microtus agrestis) have been observed to avoid traps tainted with either weasel (Mustela nivalis) anal gland secretion or red fox (Vulpes vulpes) feces (Dickman Doncaster, 1984 Stoddart, 1976). Similarly, meadow and montane voles (M pennsylvanicus and M. montanus) were observed to avoid traps treated with the principal odiferous component of fox feces, 2,5-dihydro-2,4,5-trimethyl thiazoline (Sullivan, Crump Sullivan, 1988). The laboratory experiments discussed in the present chapter provided a quantitative assessment of locomotor activity levels following exposure to predator odor in laboratory-bred meadow voles. 

Two possible sources of repellents from animals are the odors associated with mammalian carnivores and aggressive conspecifics. Rats actively avoid predator odors and this response appears to be innate. Trimethyl thiazoline extracted from fox (Vulpes vulpes) faeces caused an enclosed population of wild rats to alter their activities (Vemet-Maury, Constant Chanel, 1992). In the short-term, which may mean days or weeks, habituation to these predator odors appears to be slow. However, the odors may require reinforcement by some form of encounter with the predator itself to be effective in the longer-term (Muller-Schwarze, 1994). 

The technique of placing a predator odor within the burrow systems appears to generate an avoidance response only if all resident gophers have been previously removed. The plugging of cans and traps (presumably an anti-predator strategy) with soil in Experiments A and B, respectively. 

Response to food can be used as an indirect measure of prey response to predator scents. Stimuli can be placed either directly on the food or in close proximity to the food. For example, choice-tests were used to assess the avoidance of lion fecal odors by rabbits (Boag Mlotkiewicz 1994) and deer (Abbot et al. 1990). In both cases, subjects were offered a choice between treated and untreated pelleted food and relative intake was taken to reflect avoidance. Likewise, arena tests have been used to demonstrate that domestic livestock will investigate but reduce their ingestion of feed in the presence of predator odors (Pfister et al. 1990). Odors also can be applied to natural forage to assess whether target species avoid the treated plants (Sullivan et al. 1988 Calder Gorman 1991). Epple et al. (1995) monitored caching behavior to assess the response of mountain beaver to food resources associated with predator odors. 

Predator odors are generally aversive to potential prey species. Avoidance appears to be mediated, at least in part, by urinary constituents, which are not species-... 

Aquatic animals use their chemical senses in all aspects of their lives, from reproductive behavior to feeding, habitat selection, and predator avoidance. The hydrodynamic properties determine the possibilities and limits of chemical communication in water. As a medium, water is as dynamic as air, so that convection and advection are far more important for odor transport than is diffusion. Distribution by currents is even more important in water because compounds of similar molecular weight diffuse four orders of magnitude more slowly than in air (Gleeson, 1978). Diffusion of odorants may be important only in the submillimeter range, while turbulence is typical for water masses above the centimeter range. 

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