Discrimination of integumentary prey chemicals and strike-induced chemosensory searching in the ball python,Python regius

Experimental tests show that the ball python (Python regius) has the ability to discriminate prey chemicals from control substances by tongue-flicking and exhibits a poststrike elevation in tongue-flicking rate (PETF). Prey chemical discrimination was revealed by significantly higher number of tongue-flicks and tongue-flick attack score in response to integumental chemicals from mice than to cologne or distilled water and by a higher frequency of biting in response to prey than control chemicals. PETF was indicated by higher tongue-flicking rates after biting than in several control conditions. Concurrent movements of the body suggest the operation of strike-induced chemosensory searching (SICS). Ecological factors affecting responses to prey chemicals, including defensive behaviors and characteristics of foraging behavior related to reliance on different sensory modalities, are discussed. The presence of PETF and SICS in a henophidian snake and in scleroglossan lizards suggests that these behaviors are plesiomorphic in snakes.     

Cologne as a pungency control in tests of chemical discrimination: effects of concentration,brand, and simultaneous and sequential presentation

Cologne has been used extensively as a pungency control in experiments on chemosensory behavior to assess responses to an odorous, readily detectable stimulus that is irrelevant to the adaptive response being studied. However, undiluted cologne may be aversive, its effects might differ among brands, it might suppress responses to simultaneously presented chemical stimuli, and might affect subsequent responsiveness to other stimuli. We present experimental data showing that undiluted cologne can be aversive, but that aversion can be eliminated by dilution. We also show that the utility of cologne as a pungency control varies among brands, that cologne does not suppress responses to food chemicals in some species, but does in others, and that prior exposure to cologne does not affect later response to food chemicals. In 60 s swab trials with the Balearic lizard (Podarcis lilfordi), the main chemosensory responses were unaffected by cologne concentration. However, one-fourth of lizards exhibited slight to moderate aversion to undiluted cologne and 3:1 water:cologne, but not to a readily detected lower concentration (9:1). Two cologne brands did not affect responses, but a third brand induced increased tongue-flick rates. Colognes that stimulate increased tongue-flicking might mask real experimental effects. Cologne presented simultaneously with cricket chemicals did not affect tongue-flicking and biting responses in two species, but caused increased tongue-flicking in a third species and weaker response to cricket chemicals in a fourth. Prior testing with cologne did not affect responsiveness to cricket chemicals in a subsequent trial. Although cologne is a useful pungency control, pilot tests are needed to verify its utility for unstudied cologne types and animal species. Electronic Publication     

Apparent decoupling of prey recognition ability with prey availability in an insular snake population

Numerous studies on the feeding behavior of snakes have reported the consistency of tongue-flick responses with their natural diets. For representatives of widely distributed, dietary generalist species from particular localities, we can expect that their tongue-flick responses to potential prey unavailable in their original habitats have been reduced whereas those to prey common in the habitats have been enhanced. To test this hypothesis, intraspecific variation in tongue-flick responses to prey chemicals was examined using ingestively naive snakes (Elaphe quadrivirgata) from dietarily different populations: populations from the main Japanese island, where the snakes' diet predominantly consists of sympatric frogs, and from Mikura-jima Island, where no frogs occur and the snakes thus chiefly prey on lizards. We presented chemical stimuli from six items including those from their natural and potential prey (fish, frog, lizard, mouse, water, and cologne) to newborn snakes. Significant effects of stimuli on the tongue-flick responses were detected. On the other hand, effects of population and interaction between stimuli and population were not significant, and individual comparisons revealed no significant interlocality differences in responses to either frog or lizard chemicals. Thus, our hypothesis was not supported. However, in the Mikura-jima sample, significantly fewer snakes responded to frog chemicals than in the main island sample. The significance of the inconsistency between prey recognition ability and prey availability in the Mikura-jima population are discussed. Received: October 17, 2000 / Accepted: December 14, 2000     

Responses by a generalist predator,the Balearic lizard <Emphasis Type="Italic">Podarcis lilfordi</Emphasis>, to chemical cues from taxonomically diverse prey

Specialist predators may respond strongly to sensory cues from preferred prey, but responses by generalist predators, although predicted to be less specific, are poorly known. Among squamate reptiles, diet and strength of response to chemical prey cues covary geographically in snakes that are specialist predators. There have been no previous studies of correspondence between diet and chemosensory response in lizards that are prey generalists. Actively foraging lizards discriminate between prey chemicals and control substances. It has been speculated that differential responses among prey species are unlikely in typical species that are dietary generalists. We examined this relationship in Podarcis lilfordi, an omnivorous lacertid that consumes a wide variety of animal prey. In experiments in which chemical stimuli were presented on cotton swabs, lizards responded more strongly to chemicals from a broad spectrum of prey types than to deionized water, an odorless control. These findings plus previous data showing that P. lilfordi is capable of prey chemical discrimination suggest that P. lilfordi can identify a wide range of potential prey using chemical cues. However, there was no evidence of differential response to stimuli among prey species, even in comparisons of prey included in the natural diet and potential prey not in the diet. The results, although limited to a single species, are consistent with the hypothesis that lizard species that are prey generalists do not exhibit the differential response strengths to chemical prey cues observed in snakes that have more specialized diets. Received in revised form: 17 July 2001 Electronic Publication     

Thermal Dependence of Tongue-flicking and Comments on Use of Tongue-flicking as an Index of Squamate Behavior

Tongue-flicking rate has often been used as a dependent variable or a component of a dependent variable taken as a measure of responsiveness to chemical stimuli by lizards and snakes. Because temperature has been controlled in most studies, effects of temperature have been largely overlooked. In this study, a constant stimulus, the adult cloacal odor of a conspecific female, was presented to adult scincid lizards (Eumeces laticeps) and temperature was from 15 ° to 35 °C. Tongue-flicking rates by adult Eumeces laticeps in response to cloacal odors of conspecific females were strongly thermally dependent in 20 s and 60 s trial periods. The tongue-flick-temperature curve appears to be roughly quadratic over the entire 15 °-35 °C range studied, with very low rates at 15 ° and 20 °C followed by a rapid rise to maximum tongue-flicking rate at 30 ° and rapid decline to 35 °C. Presumably, similar relationships apply to other lizards and snakes with modifications related to ecological characteristics such as diel activity cycle and foraging mode, to relative position on a scale of eurythermy-stenothermy, and to taxon. Thermal response curves for other stimuli, especially prey odors, are likely to have the same basic form, but have not been determined.     

Tasty figs and tasteless flies: plant chemical discrimination but no prey chemical discrimination in the cordylid lizard<Emphasis Type="Italic"> Platysaurus broadleyi</Emphasis>

Lizards use visual and/or chemical cues to locate and identify food. The ability to discriminate prey chemical cues is affected by phylogeny, diet, and foraging mode. Augrabies flat lizards (Platysaurus broadleyi) are omnivorous members of the lizard clade Scleroglossa. Within Scleroglossa, all previously tested omnivores are capable of both prey and plant chemical discrimination. At Augrabies Falls National Park, P. broadleyi feed on both insects (black flies) and plant material (figs), and as scleroglossans, are predicted to discriminate both plant and prey chemicals. However, Platysaurus broadleyi use visual, not chemical cues, to detect and capture black flies, which occur in large concentrations in the study area. We tested free-ranging individuals for the ability to discriminate insect and plant chemicals from controls. There was a significant stimulus effect such that lizards tongue-flicked fig-labelled tiles significantly more than the remaining stimuli, spent more time at the fig-labelled tile, and attempted to eat fig-labelled tiles more often than tiles labelled with control or insect stimuli. Platysaurus broadleyi is exceptional in being the first lizard shown to possess plant chemical discrimination but to lack prey chemical discrimination. We suggest that an absence of prey chemical discrimination may be a consequence of foraging behaviour and environmental effects. Because insect prey are highly clumped, abundant, and aerial, profitable ambushing using visual cues may have relaxed any selective pressure favouring insect prey chemical discrimination. However, a more likely alternative is that responses to figs are gustatory, whereas as prey chemical discrimination and plant chemical discrimination are usually mediated by vomerolfaction.Communicated by P.K. McGregor     

Predatory lizards perceive plant‐derived volatile odorants

Many lizards are olfactory foragers and prey upon herbivorous arthropods, yet their responses to common herbivore‐associated plant volatiles remain unknown. As such, their role in mediating plant indirect defenses also remains largely obscured. In this paper, we use a cotton‐swab odor presentation assay to ask whether lizards respond to two arthropod‐associated plant‐derived volatile compounds: 2‐(E)‐hexenal and hexanoic acid. We studied the response of two lizard species, Sceloporus virgatusand Aspidoscelis exsanguis, because they differ substantially in their foraging behavior. We found that the actively foraging A. exsanguisresponded strongly to hexanoic acid, whereas the ambush foraging S. virgatus responded to 2‐(E)‐hexenal—an herbivore‐associated plant volatile involved in indirect defense against herbivores. These findings indicate that S. virgatus may contribute to plant indirect defense and that a species' response to specific odorants is linked with foraging mode. Future studies can elucidate how lizards use various compounds to locate prey and how these responses impact plant‐herbivore interactions.     

Responses to chemical cues from animal and plant foods by actively foraging insectivorous and omnivorous scincine lizards

If tongue-flicking is important to lizards to sample chemical cues permitting identification of foods, tongue-flicking and subsequent feeding responses should be adjusted to match diet. This hypothesis can be examined for plant foods because most lizards are insectivores, but herbivory/omnivory has evolved independently in many lizard taxa. Here we present experimental data on chemosensory responses to chemical cues from animal prey and palatable plants by three species of the scincine lizards. When tested with chemical stimuli presented on cotton swabs, the insectivorous Eumeces fasciatus responded strongly to prey chemicals but not to chemicals from plants palatable to omnivorous lizards or to pungent or odorless control stimuli. Two omnivorous species, E. schneideri and Scincus mitranus, responded more strongly to chemical cues from both prey and food plants than to the control chemicals. All available data for actively foraging lizards, including these skinks, show that they are capable of prey chemical discrimination, and insectivores do not exhibit elevated tongue-flicking or biting responses to chemical cues from palatable plants. In all of the several species of herbivores/omnivores tested, the lizards show elevated responses to both animal and plant chemicals. We suggest two independent origins of both omnivory and plant chemical discrimination that may account for the evolution of diet and food chemical discriminations in the eight species of skinks studied, five of which are omnivores. All data are consistent with the hypothesis that acquisition of omnivory is accompanied by acquisition of plant chemical discrimination, but data on a broad diversity of taxa are needed for a definitive comparative test of the evolutionary hypothesis. J. Exp. Zool. 287:327-339, 2000.     

Chemosensory responses to foods by an herbivorous acrodont lizard, <Emphasis Type="Italic">Uromastyx aegyptius</Emphasis>

Actively foraging lizards use the lingual-vomeronasal system to identify prey by chemical cues, but insectivorous ambush foragers do not. The major clade Iguania includes numerous herbivores and omnivores; among them, two iguanid and one agamine species identify plant and animal foods by tongue flicking, and data suggest that the leiolepidine Uromastyx acanthinurus may as well. We conducted experiments on chemosensory response to food by the herbivorous U. aegyptius. When chemical stimuli were presented on cotton balls in experiment 1, the lizards exhibited greater responsiveness (tongue-flick attack scores) to chemical stimuli from crickets and a preferred plant food (dandelion flowers) than from deionized water. When chemical stimuli were on ceramic tiles in experiment 2, the lizards exhibited greater total tongue flicks to cricket stimuli than to any other stimuli, and to dandelion than to deionized water. Lizards bit more frequently in response to cricket and dandelion cues than to stimuli from a nonpreferred plant (carrot) and deionized water. Tongue-flick attack scores were greater in response to cricket and dandelion stimuli than to carrot or water stimuli. These findings are consistent with the hypothesis that herbivores, even those having ambush-foraging ancestors, use chemical cues to identify potential foods. The data support the hypothesis that chemosensory responses correspond to diet. Because most lizards are generalist predators, studies of herbivorous species can provide important information on possible evolutionary adjustment of chemosensory response to dietary shifts. Electronic Publication     

Influence of prey encounter and prey identity on area-restricted searching in the lizard Pedioplanis namaquensis

We experimentally determined that the lizard Pedioplanis namaquensis engages in area-restricted searching (=ARS, localized searching after encounters with food) while foraging and that prey characteristics influence ARS. Single prey items were introduced to free-ranging lizards, and their subsequent search effort was characterized using first passage times (=FPT, time required for an animal to cross a circle of a given radius). Three prey types were used: termites, flies, and rice (control). FPTs were longer following termite encounters than following fly or control encounters. Control treatments produced no change in FPT, while lizards searching for termites showed the greatest change. The use by Pedioplanis namaquensis of ARS was most pronounced for the typically aggregated prey type.     

Marine subsidies change short‐term foraging activity and habitat utilization of terrestrial lizards

Resource pulses are brief periods of unusually high resource abundance. While population and community responses to resource pulses have been relatively well studied, how individual consumers respond to resource pulses has received less attention. Local consumers are often the first to respond to a resource pulse, and the form and timing of individual responses may influence how the effects of the pulse are transmitted throughout the community. Previous studies in Bahamian food webs have shown that detritivores associated with pulses of seaweed wrack provide an alternative prey source for lizards. When seaweed is abundant, lizards (Anolis sagrei) shift to consuming more marine‐derived prey and increase in density, which has important consequences for other components of the food web. We hypothesized that the diet shift requires individuals to alter their habitat use and foraging activity and that such responses may happen very rapidly. In this study, we used recorded video observations to investigate the immediate responses of lizards to an experimental seaweed pulse. We added seaweed to five treatment plots for comparison with five control plots. Immediately after seaweed addition, lizards decreased average perch height and increased movement rate, but these effects persisted for only 2 days. To explore the short‐term nature of the response, we used our field data to parametrize heuristic Markov chain models of perch height as a function of foraging state. These models suggest a “Synchronized‐satiation Hypothesis,” whereby lizards respond synchronously and feed quickly to satiation in the presence of a subsidy (causing an initial decrease in average perch height) and then return to the relative safety of higher perches. We suggest that the immediate responses of individual consumers to resource pulse events can provide insight into the mechanisms by which these consumers ultimately influence community‐level processes.     

Balearic lizards use chemical cues from a complex deceptive mimicry to capture attracted pollinators

Deceptive flowers from several plant species emit odors that mimic oviposition cues and attract female insects seeking for a laying site. Helicodiceros muscivorus is a species that emits an odor mimicking the foul smell of rotting meat and thereby attracts blowflies that usually oviposit on carcasses but are deceived into pollinating the plant. Thus, H. muscivorus is a striking case of pollination by brood‐site deception. The Balearic lizard, Podarcis lilfordi, exhibits remarkable interactions with dead horse arum. Balearic lizards, which sometimes forage on carcasses, are attracted to blooming dead horse arum. We showed experimentally that P. lilfordi can detect chemical cues from carcasses on cotton swabs and exhibits elevated tongue‐flick rates to carcass chemical cues compared to control stimuli. Lizards also detected and located hidden carcasses using only airborne chemical cues. The responses of lizards to chemical cues from the spadix of blooming dead horse arum were qualitatively and quantitatively similar to those to carcass odors. Therefore, the decay‐like odor that attracts blowflies for the plant's benefit also attracts lizards. This attraction may initially have been somewhat favorable for lizards that eat blowflies, but slightly unfavorable for plants because the lizards ate some pollinators. We suggest that lizards attracted by odor may have learned later to use the plant for thermoregulation and then consume its fruits, making the association more positive for lizards and benefitted arum by seed dispersal.     

How phylogeny and foraging ecology drive the level of chemosensory exploration in lizards and snakes

The chemical senses are crucial for squamates (lizards and snakes). The extent to which squamates utilize their chemosensory system, however, varies greatly among taxa and species’ foraging strategies, and played an influential role in squamate evolution. In lizards, ‘Scleroglossa’ evolved a state where species use chemical cues to search for food (active foragers), whereas ‘Iguania’ retained the use of vision to hunt prey (ambush foragers). However, such strict dichotomy is flawed as shifts in foraging modes have occurred in all clades. Here, we attempted to disentangle effects of foraging ecology from phylogenetic trait conservatism as leading cause of the disparity in chemosensory investment among squamates. To do so, we used species’ tongue‐flick rate (TFR) in the absence of ecological relevant chemical stimuli as a proxy for its fundamental level of chemosensory investigation, that is baseline TFR. Based on literature data of nearly 100 species and using phylogenetic comparative methods, we tested whether and how foraging mode and diet affect baseline TFR. Our results show that baseline TFR is higher in active than ambush foragers. Although baseline TFRs appear phylogenetically stable in some lizard taxa, that is a consequence of concordant stability of foraging mode: when foraging mode shifts within taxa, so does baseline TFR. Also, baseline TFR is a good predictor of prey chemical discriminatory ability, as we established a strong positive relationship between baseline TFR and TFR in response to prey. Baseline TFR is unrelated to diet. Essentially, foraging mode, not phylogenetic relatedness, drives convergent evolution of similar levels of squamate chemosensory investigation.     

Antipredator Behavior in Desmognathus ochrophaeus: Threat‐Specific Responses to Chemical Stimuli in a Foraging Context

Prey species may reduce the likelihood of injury or death by engaging in defensive behavior but often incur costs related to decreased foraging success or efficiency. To lessen these costs, prey may adjust the intensity or type of antipredator behavior according to the nature of the perceived threat. We evaluated the potential for threat‐sensitive responses by Allegheny Mountain dusky salamanders (Desmognathus ochrophaeus) exposed to chemical stimuli associated with predation by asking three questions: (1) Do individual D. ochrophaeus respond to chemical cues in a threat‐sensitive manner? (2) Do salamanders exhibit the same pattern of behavioral response while foraging? and (3) Is foraging efficiency reduced when focal individuals are exposed to stimuli from predators or predation events? In our first experiment, we evaluated salamander chemosensory movements (nose‐taps), locomotor activity (steps), and edge behavior in response to chemical stimuli from disturbed and injured conspecifics as well as predatory Gyrinophilus porphyriticus and found that individual D. ochrophaeus show a significant graded increase in nose‐taps when exposed to cues from conspecifics and a reduction in activity when exposed to the predator. In our second experiment, we again observed salamander responses to the same chemical stimuli but in this instance added five Drosophila prey to the test dishes. We found that salamanders exhibited a similar pattern of response to the chemical stimuli in the presence of prey, showing a graded increase in nose‐taps to cues from conspecifics and a reduction in activity when exposed to the predator. However, foraging efficiency (i.e. the proportion of successful strikes) did not vary significantly among treatments. Our data show that individual D. ochrophaeus detect and differentially respond to chemical stimuli associated with predation, but do not significantly reduce foraging efficiency. Overall, the type and relative intensity of these responses is largely unaffected by the presence of potential prey.     

Discrimination of chemical stimuli in conspecific fecal pellets by a visually adept iguanid lizard,Crotaphytus collaris

Iguanid lizards are known for visual acuity and a diminished vomeronasal organ, which has led to mixed conclusions on whether iguanids use chemical cues. The collared lizard, Crotaphytus collaris, is a territorial iguanid that lives in open rocky habitats. Fecal pellets placed prominently on open rocky perches may provide an ideal mechanism for intraspecific chemical signaling. In order to determine whether collared lizards can discriminate between chemical stimuli found in conspecific fecal pellets, we collected 24 males and 25 females to analyze sex-specific behavioral responses via tongue-flicks and a newly observed behavior for the species, gular pumps, to cotton swabs containing water, cologne, chemical stimuli from conspecific male and female fecal pellets, and the lizard’s own fecal pellet. Both sexes were able to discriminate chemical stimuli from water via at least one behavior. Male collared lizards exhibited greater rates of response (tongue-flick and gular pumps) toward male fecal pellets when compared to the negative water control. Our results also suggest individuals may be able to discriminate between fecal pellets, as indicated by generally greater (but non-significant) counts of male tongue-flick responses to male fecal pellets when compared to their own. Collared lizard chemical discrimination appears to utilize tongue-flick and gular pump behaviors, possibly associated with distinct chemosensory modes (vomerolfaction and olfaction). Based on this study, we suggest that chemical signals may play a greater role in intraspecific communication than previously thought in this highly visual lizard.     

Do lizards and snakes really differ in their ability to take large prey? A study of relative prey mass and feeding tactics in lizards

Adaptations of snakes to overpower and ingest relatively large prey have attracted considerable research, whereas lizards generally are regarded as unable to subdue or ingest such large prey items. Our data challenge this assumption. On morphological grounds, most lizards lack the highly kinetic skulls that facilitate prey ingestion in macrostomate snakes, but (1) are capable of reducing large items into ingestible-sized pieces, and (2) have much larger heads relative to body length than do snakes. Thus, maximum ingestible prey size might be as high in some lizards as in snakes. Also, the willingness of lizards to tackle very large prey items may have been underestimated. Captive hatchling scincid lizards (Bassiana duperreyi) offered crickets of a range of relative prey masses (RPMs) attacked (and sometimes consumed parts of) crickets as large as or larger than their own body mass. RPM affected foraging responses: larger crickets were less likely to be attacked (especially on the abdomen), more likely to be avoided, and less likely to provide significant nutritional benefit to the predator. Nonetheless, lizards successfully attacked and consumed most crickets ≤35% of the predator’s own body mass, representing RPM as high as for most prey taken by snakes. Thus, although lizards lack the impressive cranial kinesis or prey-subduction adaptations of snakes, at least some lizards are capable of overpowering and ingesting prey items as large as those consumed by snakes of similar body sizes.     

The Effect of Variation in Prey Movement on the Predatory Response of Jacky Lizards (Amphibolurus muricatus)

The sensory systems of animals have evolved to meet the demands of functionally critical events. Animals that rely on visual motion cues must ignore irrelevant movement and only attend to certain characteristics that warrant further consideration. For the Australian jacky lizard ( Amphibolurus muricatus ), movement is essential for detecting potential prey. Here we examine whether differences in the actual motion characteristics of a simulated prey item influence predatory behaviour. We begin with direct observations of responses to live prey items to define an ordinal scale for subsequent video playback experiments involving a synthetic prey item (an animated cricket). In expt 1, we show that the responses of lizards to the synthetic prey were matched to those given in response to video of an actual cricket. In expt 2 we manipulated the movement patterns of the synthetic cricket based on motion analysis of actual prey movement. Manipulating motion characteristics did not influence the level of predatory behaviour observed, however, lizards showed sustained predatory behaviour to stimuli with speed characteristics that were matched to those of real crickets. We discuss the possibility that recent experience of prey movement in captivity has influenced the foraging behaviour of these lizards.     

Age and Sex-Based Differences in the Use of Prey Sensory Cues in Wolf Spiders (Araneae: Lycosidae)

Differences in foraging patterns mediated by sensory cues were examined between adult and juvenile male and female wolf spiders (Schizocosa rovneri; Lycosidae). Patch residence time for thirty-one spiders were tested among juveniles and adults in artificial foraging patches. Patches varied in sensory information provided by live prey (crickets) as follows: visual stimuli alone; vibratory stimuli alone; visual and vibratory stimuli together; and control (no stimuli). Spiders moved between patches for one hour, but could not feed. Adult Schizocosa rovneri use primarily visual information to determine patch residence time, but juveniles use vibratory cues as well. Significant age and sex-based differences in the use of sensory cues suggest that observed divergent foraging strategies are partly due to the use of different perceptual cues in prey detection.     

Absence of Prey Chemical Discrimination by Tongue-flicking in an Ambush-foraging Lizard Having Actively Foraging Ancestors

Lingually mediated detection of prey chemicals is widespread in one major clade of lizards, Scleroglossa, but rare in the other, Iguania. It is absent in all ambush-foraging families tested and present in all actively foraging families. In Iguania, prey chemical discrimination is known only in the herbivorous Iguanidae; in Scleroglossa, it was heretofore known to be absent only in ambush-foraging gekkonids. Because ambush foraging precludes lingual sampling of a wide area and tongue-flicking would disrupt the crypticity ambushers maintain by immobility, we predicted that prey chemical discrimination would be absent in scleroglossans that have secondarily adopted ambush foraging. The Cape girdled lizard, Cordylus cordylus, is member of Cordylidae, a family of ambush foragers considered derived from active foragers in the Autarchoglossa, a group of scleroglossan families having highly developed lingual chemosensory behaviours. As predicted, this species did not discriminate surface chemicals of three prey species from control substances in a series of standardized experiments in which prey chemicals were presented on cotton-tipped applicators. Thus, even in taxa having highly developed prey chemical discrimination, adoption of ambush foraging may induce loss of prey chemical discrimination, providing further and stronger evidence that prey chemical discrimination is adaptively adjusted to foraging mode.     

Olfactory predator recognition in the brown mouse lemur (Microcebus rufus) in Ranomafana National Park,Madagascar

Predator odors such as urine and feces are known to elicit antipredator behaviors in prey including avoidance, fear, and curiosity. We measured how wild brown mouse lemurs (Microcebus rufus) responded to odors of mammalian, avian, and snake predators as well as nonpredator controls. The first experiment took place under controlled conditions in a laboratory where we recorded the occurrence of four behavioral categories (ignore, curiosity, alert, and fear) in response to a single odor. Subjects exhibited behavioral change significantly more often in response to the predator than to control stimuli, but did not distinguish between familiar and unfamiliar predators. Mammalian predator urine and feces were most likely to elicit behavioral change. The owl was the only predator to never elicit behavioral change, possibly because owls do not provide relevant odor cues. A second experiment employing live traps in the forest found that neither predator nor control odors affected the likelihood of capture. Due to their longevity, odors do not provide accurate information of spatial and temporal risk, and while mouse lemurs may have initially hesitated to enter a trap, in the absence of additional information about risk, they may have eventually ignored the stimuli. This study found that brown mouse lemurs are able to distinguish between predator and nonpredator odors, and that risk assessment may be affected by the experience, as well as predator and sensory stimulus quality.