Responses of Wild Norway Rats (Rattus norvegicus) to Predator Odors

If rats could be shown to avoid the odors of predators, then conservation managers could manipulate this behavior to exclude rats from important conservation sites. We evaluated the ability of six predator odors to elicit avoidance responses by wild-caught Norway rats (Rattus norvegicus) from two New Zealand populations (Kapiti Island and North Island). Kapiti Island is free of mammalian predators, while the North Island has established populations of felids, canids, and mustelids. Three of the predator odors were real and three were synthesized volatile ingredients of real animal feces or urine. We compared the rats' responses to predator odors with their responses to three natural herbivore odors. We used a Y maze, and rats were offered the choice of an odor in one arm of the maze and distilled water in the other arm. Each choice arm was ducted at the entrance to remove air and the odor. We recorded: (1) the time until the rat left the first arm of the maze, (2) the time until the rat visited each arm, (3) the number of visits to each arm, (4) the amount of time spent in each arm, and (5) a total activity score for each rat. Kapiti rats showed an aversion to five of the six predator odors, despite never having encountered them before. Kapiti rats visited herbivore odors more often than carnivore odors and were less active in the presence of carnivore odors than they were when tested with herbivore odors. In addition, Kapiti rats approached some herbivore odors more quickly than they approached carnivore odors. North Island rats appeared to avoid cat urine, but despite being predator experienced, did not show a consistent aversion to the carnivore odors we tested. Both samples of rats, but particularly the North Island group, showed high individual variation. We conclude that predator odors are unlikely to be an effective management tool for all populations of this species of rat because of this high individual variability and the likelihood that each island population will differ in its responses to a given odor.     

Laboratory Evaluation of Predator Odors for Eliciting an Avoidance Response in Roof Rats (Rattus rattus)

We evaluated eight synthetic predator odors and mongoose (Herpestes auropunctatus) feces for eliciting avoidance responses and/or reduced feeding by wild captured Hawaiian roof rats (Rattus rattus). In a bioassay arena, we recorded: (1) time until each rat entered the arena, (2) time elapsed until first eating bout, (3) time spent in each half of the arena, (4) number of eating bouts, and (5) consumption. Rats displayed a response to the predator odors in terms of increased elapsed time before initial arena entry and initial eating bout, a lower number of eating bouts, and less food consumption than in the respective control groups. The odor that produced the greatest differences in response relative to the control group was 3,3-dimethyl-1,2-dithiolane [from red fox (Vulpes vulpes) feces and mustelid anal scent gland]. Mongoose fecal odor produced different responses in four of the five variables measured while (E,Z)-2,4,5-trimethyl-³-thiazoIine (red fox feces) and 4-mercapto-4-methylpentan-2-one (red fox urine and feces) odors were different from the control group in three of the five variables measured. These laboratory responses suggest that wild Hawaiian roof rats avoid predator odors.     

Effect of predator odors on heart rate and metabolic rate of wapiti (Cervus elaphus canadensis)

We measured the heart rate (HR) and oxygen consumption ( ) of wapiti (Cervus elaphus canadensis) before, during, and after presentation of biologically irrelevant odors (pentane, thiophene, and a perfume), artificial predator odors (an ether extract of cougar feces, and PDT, a compound found in mustelid anal gland secretion), stale predator odors (dog feces and urine and fox urine, kept at ambient temperature for a few weeks), and fresh predator odors (wolf, coyote, and cougar feces and the odor of a dead coyote, kept frozen between collection and test). Overall, responses to odors were small compared to other stressful stimuli. Individual variability was high among scents and among wapiti, but two of the fresh predator odors (cougar and wolf feces) produced larger HR and responses than the other scents and were more often successful at producing responses. As a group, fresh predator odors produced larger tachycardias and elicited a larger number of significant HR responses than biologically irrelevant novel odors. although the two classes of odors did not differ in their effect on . Although several other studies have shown that ungulates have reduced feeding levels when their food is scented with predator odors, it is not clear if this is due to reduced palatability or antipredator behavior. This study is the first demonstration that a wild ungulate species reacted more strongly to predator odors than to other odors in a nonfeeding situation.     

Exposure to Urine of Canids and Felids, but not of Herbivores, Induces Defensive Behavior in Laboratory Rats

Predator odors induce defensive behavior in many prey species. For various reasons, studies carried out up to now have been unable to establish whether predator odor recognition is innate or not. Mostly, only particular odors or wild-living (i.e., experienced) test animals have been used in these studies, restricting the conclusiveness of the observations. In the present study, the behavioral effects of exposure to different predator odors on predator odor-naive laboratory male rats were compared with the effects of different nonpredator odors and of a no-odor control stimulus. Results show that exposure to urine of canids and felids, but not of herbivores or conspecifics, induce defensive behaviors. Taken together, the study provides support for the hypothesis that there is an innate recognition of predator odors in laboratory rats.     

Use of Chemical Communication by the Subterranean Rodent Ctenomys talarum (Tuco-Tuco) During the Breeding Season

Solitary subterranean rodents with a low frequency of direct contact between conspecifics are expected to use chemical communication to coordinate social and reproductive behavior. We examined whether reproductive tuco-tucos (Ctenomys talarum) were able to discriminate the reproductive condition, sex, and source population of conspecifics by means of chemical cues contained in urine, feces, soiled shavings, or anogenital secretions. During preference tests in which animals had direct contact with these chemical cues, tuco-tucos were able to determine the reproductive condition of opposite sex conspecifics independent of the source of odor. When only olfactory cues were available, both sexes discriminated reproductive condition of opposite sex individuals using urine. Females were also able to discriminate the reproductive condition of males using soiled shavings. Females spent more time investigating male odors than female odors; except in the case of feces, breeding males spent similar amounts of time investigating male and female odors. No preferences were detected for opposite sex urine from members of an animal's own versus another population. The role of chemical cues in territory defense and breeding performance by this highly territorial subterranean rodent is discussed.     

Responses of beaver (Castor canadensis Kuhl) to predator chemicals

Free-ranging beaver (Castor canadensis) in two different beaver populations in New York State were exposed to predator chemicals to test feeding inhibition. Solvent extracts of feces were applied to stem sections of aspen, the preferred food tree of beavers, permitting smelling and tasting the samples. Predator odors were from wolf (Canis lupus), coyote (Canis latrans), dog (Canis familiaris), black bear (Ursus americanus), river otter (Lutra canadensis), lynx (Lynx canadensis), and African lion (Panthera leo). The experiment was repeated. The predator odors reduced feeding compared to untreated or solvent-treated controls. One population consumed 17.0% of the samples with predator odor and 27.0% of the controls in summer, and 48.4% and 60.0%, respectively, in autumn. The other population accepted 3.15% of the predator odor samples and 11.05% of the controls in summer. Coyote, lynx, and river otter odors had the strongest effects. Diesel oil and bitter-tasting neem extract had weaker effects. Predator odors are promising as feeding repellents for beaver.     

Laboratory Evaluation of Odor Preferences of the Brushtail Possum

The Australian brushtail possum (Trichosurus vulpecula) is the major vertebrate pest in New Zealand. Possums cause significant damage to the country's native and exotic forests and, as a vector of bovine tuberculosis, are a serious threat to the country's meat industry. Strong smelling odors are often used as lures during possum control operations in New Zealand, but little is known about the preferences of possums for these odurs. A test was designed to determine the preferences of captive wild possums for a number of odors commonly used as lures. To assess the effectiveness of the method, the possums were tested for their responses to a familiar food odor (apple) versus no odor. The possums spent significantly more time investigating the apple odor and also sniffed it more often than the no-odor control in the 15-min test period. The same procedure, however, showed that five odors commonly used as lures (almond, cloves, cinnamon, peanut, and orange) were no more preferable than water. Our results suggest that these unfamiliar odors are either equally attractive or unattractive to possums and that odors that are more familiar to these animals may be more appropriate as lures.     

Chemical characterization of fruit and fungal volatiles attractive to dried-fruit beetle,Carpophilus hemipterus (L.) (Coleoptera: Nitidulidae)

The chemical basis underlying orientation to fruit and fungal odors was investigated for the dried-fruit beetle,Carpophilus hemipterus (L.). In wind-tunnel bioassays of walking and flight response from 1.8 m, beetles were attracted to odors of the yeastSaccharomyces cerevisiae on agar, aseptic banana, or banana inoculated withS. cerevisiae, although both banana substrates elicited greater response than the yeast alone. When presented in a two-choice bioassay, the yeast-inoculated banana attracted approximately twice as many beetles as did the aseptic banana. GC-MS analysis of the headspace volatiles above these odor sources revealed a somewhat more complex and concentrated volatile profile for yeast-inoculated banana than for aseptic banana. The odor from yeast on agar had fewer components, and these were present at lower concentrations than the odors of either banana substrate. By blending mineral-oil or aqueous solutions of the 18 components of inoculated-banana odor in varying concentrations, it was possible to mimic closely the headspace profile of the natural odor. This synthetic odor also elicited beetle attraction in the wind tunnel at levels comparable to the inoculated banana. Through a series of bioassays in which individual components were subtracted from or added to a synthetic odor blend, it was determined that ethyl acetate, acetaldehyde, 2-pentanol, and 3-methylbutanol comprised the simplest blend of compounds evoking full behavioral response. However, 2-methylpropanol or butanol were apparently interchangeable with 3-methylbutanol in this blend, and comparable response could also be elicited by replacing acetaldehyde with a combination of both 2-pentanone and 3-hydroxy-2-butanone. Thus, our results suggest that this generalist insect herbivore locates its hosts by a long-range response to a variety of blends of common fruit volatiles, whose concentrations are enhanced by fungi.     

Foraging Behavior and Microhabitat Use by Spiny Mice, Acomys cahirinus and A. russatus, in the Presence of Blanford's Fox (Vulpes cana) Odor

We investigated the responses of common and golden spiny mice (Acomys cahirinus and A. russatus, respectively) to the fecal odor of Blanford's fox (Vulpes cana), a predator of Acomys, which overlaps in habitat use with the mice. Neither species of mouse showed a significant response to the presence of fox odor compared with the presence of the fecal odor of a local herbivore (Nubian ibex, Capra ibex nubia). One explanation is that the impact of predation from V. cana may be sufficiently low that the cost of avoidance, in terms of missed feeding opportunities, conveys little selective advantage. Alternatively, fecal odor may not provide a focused cue of immediate danger for spiny mice. The diurnal A. russatus showed a stronger (near significant) response than the nocturnal A. cahirinus to fecal odor of this nocturnal predator. This may be a legacy of the underlying nocturnal activity rhythm of A. russatus or may indicate a generally more cautious response to predator odors, as A. russatus has a much stronger preference for sheltered microhabitats than A. cahirinus.     

Field Testing Synthetic Predator Odors for Roof Rats (Rattus Rattus) in Hawaiian Macadamia Nut Orchards

Field trials were conducted to determine whether the synthetic predator odors 3,3-dimethyl-l,2-dithiolane (DMDIT) and (E,Z)-2,4,5-tri-methyl-³-thiazoline (TMT) were effective at eliciting a behavioral response in wild roof rats (Rattus rattus). The study site was a Hawaiian macadamia nut (Macadamia integrifotia) orchard with a recent history of roof rat feeding damage. The synthetic predator odors were encapsulated in urethane devices secured to tree branches. Mark-recapture data from live-trapping of rats and radio telemetry location data were used to assess behavioral responses of rats to the predator odors. Mark–recapture data indicated that DMDIT and TMT had no effect on capture numbers, reproduction, or body weight of rats. There was some indication that distribution of captures and number of locations relative to treated trees in TMT areas were less than in controls, but this pattern was not significant. The predator odors had no effect on home range or median distance from center of activity (MDIS) of rats as measured by telemetry. There was a trend of increasing values of MDIS on TMT areas in session 1 but not session 2. Overall we could not detect significant differences or consistent trends in responses of rats to DMDIT or TMT in these field trials.     

Use of predator odors as repellents to reduce feeding damage by herbivores

The effectiveness of predator odors (fecal, urine, and anal scent gland) in suppressing feeding damage by snowshoe hares was investigated in pen bioassays at the University of British Columbia Research Forest, Maple Ridge, British Columbia, Canada. A total of 28 bioassay trials tested the effects of these odors on hare consumption of willow browse and coniferous seedlings. Lynx and bobcat feces, weasel anal gland secretion, and lynx, bobcat, wolf, coyote, fox, and wolverine urines resulted in the most effective suppression of hare feeding damage. Novel odors of domestic dog urine and 2-methylbutyric acid did not reduce feeding. A field bioassay with lodgepole pine seedlings and weasel scent provided significant results comparable to the pen bioassays. The short-term (up to seven days) effectiveness of these treatments was more likely due to evaporative loss of the active repellent components of a given odor than habituation of hares to the stimulus. Predator odors as repellents have a biological basis compared with the anthropomorphic origins of commercial repellents. When encapsulated in weather-proof controlled-release devices, these odors could provide long-term protection for forestry plantations and agricultural crops which experience hare/rabbit feeding damage.     

Do Pine Voles (Microtus pinetorum) Use Numerous Types of Olfactory Cues to Discriminate Gender?

Olfactory cues can contain information for discrimination of gender that can affect subsequent social interactions. Social rodents are hypothesized to use more olfactory cues than nonsocial rodents to distinguish males from females. The generality of this hypothesis was tested using the pine vole (Microtus pinetorum), a social vole. We examined nine possible sources of odors. A slide containing an odor from a male and a female was presented to each test subject for 3 min. We recorded the amount of time each test subject spent investigating each odor. Females spent significantly more time investigating male urine and male anogenital odors; however, they did not use any other odor sources to discriminate gender. In contrast, males did not use any odor sources to discriminate gender. Our results do not support the hypothesis that all social rodents use numerous odor sources to discriminate gender. Instead, our results are consistent with the alternative hypothesis that use of odor sources to convey information about gender may differ in rodents that live in different microhabitats.     

Which Chemical Constituents from Dog Feces are Involved in its Food Repellent Effect in Sheep?

This study is an attempt to identity the active chemicals (signal) of the odor of dog feces that suppress feeding in domestic sheep. The repellent effects of the odors of dog, wolf, pig, and sheep feces (potential predator and nonpredator species) were assessed on sheep, using a food-choice situation. The odors of wolf and dog feces had the highest repellent effect. A total pentane extract of dog feces was split by micropreparative gas chromatography and the fractions obtained were analyzed and presented to sheep in a food-choice situation. The quantitatively major constituents of the pentane extract, identified by gas chromatography–mass spectrometry, are indole and fatty acids. In food repellency tests, indole had no repellent effect. The active odorous signal contained in dog feces appears to consist of fatty acids mixed with neutral compounds acting synergically. These experiments underline the complexity of this biological signal and constitute a first step in the development of a practical repellent for ungulates.     

Use of odor baits in traps to test reactions to intra- and interspecific chemical cues in house mice living in outdoor enclosures

House mice (Mus musculus) living in outdoor enclosures were tested for urinary chemical cue preferences using odor-baited traps. In the first experiment, with only volatile cues available, odors from conspecific males and females of various age classes and reproductive conditions were tested; no preferences were exhibited. In the second experiment mice had both nonvolatile and volatile cues available from the same sources as in experiment I. All age and sex class and female reproductive condition groups exhibited odor cue preferences except juvenile females. There were no specific odor cue preferences exhibited by any of the responder types with regard to odors from juvenile females. In the third and fifth experiments, mice were presented with nonvolatile plus volatile or only volatile urine odor cues, respectively, from four genera,Mus, Peromyscus, Microtus, andHomo. Mice of all age classes and both sexes preferredMus musculus odor, were neutral towardMicrotus ochrogaster odor, and avoided odors fromPeromyscus leucopus andHomo sapiens; these patterns were the same regardless of whether only volatile or both volatile and nonvolatile cues were presented. The fourth and sixth experiments involved testing volatile cues only and volatile cues plus nonvolatile cues from human sweat or feces from dogs, cats, or shrews. Mice avoided the human sweat and feces from cats and shrews, but were neutral toward the odor of dog feces. There were effects on whether mice were trapped in the interior of the enclosure or on the perimeter for some odors tested in these six experiments. The findings provide insights regarding possible functions of odor cues in the behavioral ecology of house mice. Odor-baiting traps can be an effective tool with respect to testing some, but not all questions pertaining to olfactory cues and house mouse social biology.     

Toluene and weasel (2-propylthietane) odors suppress feeding in the rat

The odors of toluene and 2-propylthietane have been shown to elicit fast wave bursts of 15–30 Hz in the olfactory bulb and dentate gyrus of rats. The odors of cadaverine, butyric acid, and caproic acid were found to be ineffective by comparison. The present study investigated feeding in rats offered a choice between food pellets treated with one of the above mentioned odors or untreated pellets. Unscented pellets were also presented in a control condition. The results indicate that 2-propylthietane or toluene scented food is avoided; cadaverine scented food is preferred; but caproic acid and butyric acid scents have no effect. Toluene and 2-propylthietane may activate central pathways involved in predator detection/avoidance, while cadaverine may activate pathways involved in approach and feeding behavior.     

The Role of Fresh <Emphasis Type="Italic">versus</Emphasis> Old Leaf Damage in the Attraction of Parasitic Wasps to Herbivore-Induced Maize Volatiles

The odor produced by a plant under herbivore attack is often used by parasitic wasps to locate hosts. Any type of surface damage commonly causes plant leaves to release so-called green leaf volatiles, whereas blends of inducible compounds are more specific for herbivore attack and can vary considerably among plant genotypes. We compared the responses of naïve and experienced parasitoids of the species Cotesia marginiventris and Microplitis rufiventris to volatiles from maize leaves with fresh damage (mainly green leaf volatiles) vs. old damage (mainly terpenoids) in a six-arm olfactometer. These braconid wasps are both solitary endoparasitoids of lepidopteran larvae, but differ in geographical origin and host range. In choice experiments with odor blends from maize plants with fresh damage vs. blends from plants with old damage, inexperienced C. marginiventris showed a preference for the volatiles from freshly damaged leaves. No such preference was observed for inexperienced M. rufiventris. After an oviposition experience in hosts feeding on maize plants, C. marginiventris females were more attracted by a mixture of volatiles from fresh and old damage. Apparently, C. marginiventris has an innate preference for the odor of freshly damaged leaves, and this preference shifts in favor of a blend containing a mixture of green leaf volatiles plus terpenoids, after experiencing the latter blend in association with hosts. M. rufiventris responded poorly after experience and preferred fresh damage odors. Possibly, after associative learning, this species uses cues that are more directly related with the host presence, such as volatiles from host feces, which were not present in the odor sources offered in the olfactometer. The results demonstrate the complexity of the use of plant volatiles by parasitoids and show that different parasitoid species have evolved different strategies to exploit these signals.     

Pulsed Odors from Maize or Spinach Elicit Orientation in European Corn Borer Neonate Larvae

Lepidoptera larvae are capable of orienting towards or away from plants by using odors as cues but whether this attraction is innate or secondarily acquired remains unknown. We tested the hypothesis that European corn borer (ECB) neonate larvae express an innate attraction towards odors released from maize, and avoidance towards odors from spinach. Neonate larvae were placed on a locomotion compensator within a constant stream of humidified air that was loaded intermittently with airborne odors drawn from potted plants. The odor stream was delivered continuously or pulsed (1 to 10 sec pulses) at 40 ml/min. ECB larvae oriented toward maize odors pulsed at 2 to 6 sec but walked away from maize odors delivered at lower frequencies (9 and 10 sec pulses or to continuous ones). They consistently walked away from spinach odors, irrespective of the pulsing regime except at 1 sec pulses that did not elicit orientation. We further explored odor intensity on orientation towards maize odors by adjusting the odor stream intensity. At higher intensity (60 ml/min), the direction reversal started at the 6 sec half period, while at lower intensity (20 ml/min), it showed up only for the continuous stimulus. ECB larvae exhibit a striking ability to lock on to a direction, which they maintained despite gaps of up to 10 sec in the odor stream. Our results demonstrate that ECB neonate larvae express innate orientation preferences towards natural odors from plants. These reactions correlate well with the biological value of these plants for ECB: maize generally is accepted by ECB larvae and adults, while spinach represents a poor host because it produces (non-volatile) phytoecdysteroids that are toxic and deterrent.     

Exposure to Predator Odor Reduces Locomotor Activity Levels in Adult Male Rats: Lack of Effect of Hippocampal Lesion

The hippocampus has been implicated in mediating responses to predators. Involvement of the hippocampus was tested in the present study in which a multivariate analysis of the locomotor activity of intact and hippocampectomized (destruction of dentate and CA1 cells) laboratory rats, Rattus norvegicus, was conducted following exposure to a predator odor. Levels of various activity variables were monitored in an automated activity monitoring system following a brief 3-min exposure to 2-propylthietane (weasel odor), caproic acid (goat odor), toluene (organic solvent), and a no-odor condition in hippocampal-lesioned (using colchicine) and sham-operated control male rats. Rats of both groups displayed reduced levels of total distance, movement time, vertical activity, and number of movements following exposure to weasel odor and toluene in comparison to the no-odor condition. Exposure to goal odor resulted only in reduced levels of vertical activity and number of movements. There were no differences in activity levels between hippocampal-lesioned and sham-operated rats during baseline activity recording or following exposure to any of the odors. However, hippocampal-lesioned rats spent less lime in the center of the activity boxes than sham-operated control rats across all conditions. This study demonstrates that laboratory rats show marked changes in locomotion in response to the odor of a predator and suggests that an intact hippocampus is not essential for mediating these responses.     

Sex-identifying urine and molt signals in lobster (Homarus americanus)

During courtship, premolt female lobsters,Homarus americanus, choose a male and initiate a pair bond by repeated approaches to his shelter. The male allows such a female to share his shelter for about one week. This knowledge formed the basis to search for quantitative evidence for lobster sex pheromone(s) used in courtship: male cues to allow premolt females to identify a preferred male, and female cues to allow males to identify a premolt mature female. In each of four 1500-liter naturalistic aquaria, the behavioral responses of one female and two male lobsters to male and female lobster urine (0.5 ml) and body odor (20 ml) stimuli were observed. These stimuli were injected once or twice per day into a continuously flowing delivery tube attached to lobster shelters. Habituation to stimulus introduction—a serious problem in earlier experiments—was apparently avoided in the more natural social and physical environment we employed in these experiments. We demonstrated that male and female molt body odors contain different chemical substances: females responded to male molt body odor and males responded to female molt body odor but not vice versa. In general, male and female intermolt urine caused strong responses; however, females responded only weakly to male urine. This suggests that male and female urine are chemically different. Female urine and molt body odor caused a typically male high-on-legs response. These results show that molt body odors and intermolt urine contain sex-specific substances, which may be used in lobster courtship as well as other social interactions.     

Sheep food repellents: Efficacy of various products,habituation, and social facilitation

The study of food repulsion in ungulates is of practical importance for controlling browsing damage to forest trees and agricultural crops. Experiments with domestic sheep assessed the repulsive value of three natural and two synthetic products, using a food-choice situation. Animals were individually presented with two troughs, each containing 30 g of maize, one treated with a chemical product, and the other a control. The odor of domestic dog feces appeared to be highly repulsive, as none of the treated food was eaten, whereas 3 g ±9 and 6 g ±10 were eaten, respectively, of food treated with fetal fluids from sheep and odor of pig feces. Synthetic odors of lion feces and a commercial deer repellent were less efficient as repellents with 11 g ±13 and 14 g ±15 of food eaten, respectively. Habituation to three of the repellents was tested for a minimum of seven successive days. With dog feces, no habituation to the odor was observed. On the contrary, significant habituation (P < 0.05) was observed as early as the third trial for sheep fetal fluids and the fourth trial for the commercial repellent. To test for the effects of social facilitation, groups of four sheep including no, one, or two anosmic animals were presented with food treated with the odor of dog feces. No social facilitation was observed as none of the intact sheep ate any of the food, although the anosmic animals actively ate it throughout the test. In individual food choice tests, the odor of dog feces appeared to be an especially efficient repellent when compared with the other natural or synthetic products. Such repulsion was nearly complete, and neither habituation nor social facilitation could be observed.