Knowing the Risk: Crickets Distinguish between Spider Predators of Different Size and Commonness

Predators unintentionally release chemical and other cues into their environment that can be used by prey to assess predator presence. Prey organisms can therefore perform specific antipredator behavior to reduce predation risk, which can strongly shape the outcome of trophic interactions. In contrast to aquatic systems, studies on cue‐driven antipredator behavior in terrestrial arthropods cover only few species to date. Here, we investigated occurrence and strength of antipredator behavior of the wood cricket Nemobius sylvestris toward cues of 14 syntopic spider species that are potential predators of wood crickets. We used two different behavioral arena experiments to investigate the influence of predator cues on wood cricket mobility. We further tested whether changes in wood cricket mobility can be explained by five predator‐specific traits: hunting mode, commonness, diurnal activity, predator–prey body–size ratio, and predator–prey life stage differences. Crickets were singly recorded (1) in separate arenas, either in presence or absence of spider cues, to analyze changes in mobility on filter paper covered with cues compared with normal mobility on filter paper without cues; and (2) in subdivided arenas partly covered with spider cues, where the crickets could choose between cue‐bearing and cue‐less areas to analyze differences in residence time and mobility when crickets are able to avoid cues. Crickets either increased or reduced their mobility in the presence of spider cues. In the experiments with cues and controls in separate arenas, the magnitude of behavioral change increased significantly with increasing predator–prey body size ratio. When crickets could choose between spider cues and control, their mobility was significantly higher in the presence of cues from common spider species than from rare spiders. We therefore conclude that wood crickets distinguish between cues from different predator species and that spiders unintentionally release a species‐specific composition and size‐dependent quantity of cues, which lead to distinct antipredator behavior in wood crickets.     

Pigeons’ (Columba livia) hierarchical organization of local and global cues in touch screen tasks

Redundant encoding of local and global spatial cues is a common occurrence in many species. However, preferential use of the each type of cue seems to vary across species and tasks. In the current study, pigeons (Columba livia) were trained in three experiments on a touch screen task which included redundant local positional cues and global spatial cues. Specifically, pigeons were required to choose the middle out of three choice squares, such that the position within the array provided local information and the location on the screen provided global information. In Experiment 1, pigeons were trained and tested on vertically aligned arrays. In Experiment 2, pigeons were trained and tested on horizontally aligned arrays, and in Experiment 3, pigeons were trained and tested with vertical, horizontal and diagonally aligned arrays. The results indicate that preference for cue type depends upon the type of spatial information being encoded. Specifically, on vertical and diagonally aligned arrays, pigeons preferred global cues, whereas on horizontally aligned arrays, pigeons preferred local cues.     

The internet as a research tool in the study of associative learning: an example from overshadowing

The present study aimed to replicate an associative learning effect, overshadowing, both in the traditional laboratory conditions and over the internet. The experimental task required participants to predict an outcome based on the presence of several cues. When a cue that was always trained together with a second cue was presented on isolation at test, the expectancy of the outcome was impaired, which revealed overshadowing. This experimental task was performed by undergraduate students (N=106) in the laboratory and by a different set of anonymous participants over the internet (N=91). Similar levels of overshadowing were obtained in both locations. These similarities show that web-delivered experiments can be used as a complement of traditional experiments.     

Does General Motivation Energize Financial Reward-Seeking Behavior? Evidence from an Effort Task

We aimed to predict how hard subjects work for financial rewards from their general trait and state reward-motivation. We specifically asked 1) whether individuals high in general trait “reward responsiveness” work harder 2) whether task-irrelevant cues can make people work harder, by increasing general motivation. Each trial of our task contained a 1 second earning interval in which male subjects earned money for each button press. This was preceded by one of three predictive cues: an erotic picture of a woman, a man, or a geometric figure. We found that individuals high in trait “reward responsiveness” worked harder and earned more, irrespective of the predictive cue. Because female predictive cues are more rewarding, we expected them to increase general motivation in our male subjects and invigorate work, but found a more complex pattern.     

Predator–prey interactions between crayfish (Orconectes juvenilis) and snails (Physa gyrina) are affected by spatial scale and chemical cues

Abstract. We conducted two experiments to compare the behaviors of predatory crayfish ( Orconectes juvenilis ) and snail prey ( Physa gyrina ), with and without exposure to injured-snail cues, in seven different sizes of arena. Individuals in both O. juvenilis and P. gyrina are known to obtain information about predation events from chemical cues present in the water, but the effect of spatial scale on this information or the ensuing interaction has not been previously investigated. We found that crayfish were generally more active in larger arenas, but their response to injured-snail cues decreased as arena size increased. Snails responded to injured-snail cue by seeking refuge, but responded less strongly in larger arenas. Less time was required for crayfish to capture a snail in the presence of injured-snail cue, and there was an interaction between cue and arena size evident in middle-sized arenas. Consumption time was lower in the presence of injured-snail cue but was unaffected by arena size. Based on these results, we conclude that the effects of injured-snail cue are mediated by spatial scale, and this affects the outcome of this predator–prey interaction. Spatial scale should be considered in the design and interpretation of other predator–prey studies, particularly when sensory or motility differences exist between predators and prey that affect how each gathers information about the environment.     

Stay Tuned: What Is Special About Not Shifting Attention?

Background

When studying attentional orienting processes, brain activity elicited by symbolic cue is usually compared to a neutral condition in which no information is provided about the upcoming target location. It is generally assumed that when a neutral cue is provided, participants do not shift their attention. The present study sought to validate this assumption. We further investigated whether anticipated task demands had an impact on brain activity related to processing symbolic cues.

Methodology/Principal Findings

Two experiments were conducted, during which event-related potentials were elicited by symbolic cues that instructed participants to shift their attention to a particular location on a computer screen. In Experiment 1, attention shift-inducing cues were compared to non-informative cues, while in both conditions participants were required to detect target stimuli that were subsequently presented at peripheral locations. In Experiment 2, a non-ambiguous “stay-central” cue that explicitly required participants not to shift their attention was used instead. In the latter case, target stimuli that followed a stay-central cue were also presented at a central location. Both experiments revealed enlarged early latency contralateral ERP components to shift-inducing cues compared to those elicited by either non-informative (exp. 1) or stay-central cues (exp. 2). In addition, cueing effects were modulated by the anticipated difficulty of the upcoming target, particularly so in Experiment 2. A positive difference, predominantly over the posterior contralateral scalp areas, could be observed for stay-central cues, especially for those predicting that the upcoming target would be easy. This effect was not present for non-informative cues.

Conclusions/Significance

We interpret our result in terms of a more rapid engagement of attention occurring in the presence of a more predictive instruction (i.e. stay-central easy target). Our results indicate that the human brain is capable of very rapidly identifying the difference between different types of instructions.     

What Happens in Between? Human Oscillatory Brain Activity Related to Crossmodal Spatial Cueing

Previous studies investigated the effects of crossmodal spatial attention by comparing the responses to validly versus invalidly cued target stimuli. Dynamics of cortical rhythms in the time interval between cue and target might contribute to cue effects on performance. Here, we studied the influence of spatial attention on ongoing oscillatory brain activity in the interval between cue and target onset. In a first experiment, subjects underwent periods of tactile stimulation (cue) followed by visual stimulation (target) in a spatial cueing task as well as tactile stimulation as a control. In a second experiment, cue validity was modified to be 50%, 75%, or else 25%, to separate effects of exogenous shifts of attention caused by tactile stimuli from that of endogenous shifts. Tactile stimuli produced: 1) a stronger lateralization of the sensorimotor beta-rhythm rebound (15-22 Hz) after tactile stimuli serving as cues versus not serving as cues; 2) a suppression of the occipital alpha-rhythm (7-13 Hz) appearing only in the cueing task (this suppression was stronger contralateral to the endogenously attended side and was predictive of behavioral success); 3) an increase of prefrontal gamma-activity (25-35 Hz) specifically in the cueing task. We measured cue-related modulations of cortical rhythms which may accompany crossmodal spatial attention, expectation or decision, and therefore contribute to cue validity effects. The clearly lateralized alpha suppression after tactile cues in our data indicates its dependence on endogenous rather than exogenous shifts of visuo-spatial attention following a cue independent of its modality.     

Effects of conditioning history on selective stimulus control by elements of compound discriminative stimuli

Effects of prior discrimination training on stimulus control by color and shape dimensions of compound stimuli were studied with college students. In Phase 1, single-stimulus discrimination training was conducted for two values of color and shape. Phase 2 discrimination training employed two 2-dimensional compound stimuli composed of the color and shape stimuli trained in Phase 1. For conflict-compound stimuli, the stimulus-response-consequence contingency was altered between phases for one stimulus dimension (target dimension), but not for the other, non-target, dimension. Level of congruence (100%, 25%, and 0%) of the contingency for the target dimension between phases was manipulated across groups. When each stimulus value was tested in Phase 3, level of Phase-2-consistent responding to the target dimension varied with level of Phase-1-to-Phase-2 congruence. In Experiment 2, training history for the non-target dimension was altered across three conditions: (a) Correlated with reinforcement, as in Experiment 1, (b) No-Training, or (c) Not-Correlated. Phase-2-consistent responding to the target cue in Phase 3 was lower under the latter conditions than under the Correlated condition, indicating that the non-target dimension modulated control by the target dimension, consistent with stimulus competition. The data suggest elemental, rather than configural processing of the compound stimuli during Phase 2.     

Effects of cue information on response production and inhibition measured by event-related potentials

The aim of this study was to investigate how information carried by a cue stimulus modulate event-related potentials (ERPs) to a subsequent target stimulus which either calls for an overt response (Go stimulus) or no response (Nogo stimulus). One of the cues predicted the likely appearance of the Go stimulus (Go cue) whereas the other cue predicted the likely appearance of the Nogo stimulus (Nogo cue). Our results showed that unpredicted Nogo stimuli elicited enlarged N200 component. This finding supports the notion that Nogo N200 reflects response inhibition processes, i.e., the amplitude of the N200 is a function of the difficulty of response inhibition. In other words, increased N200 to Nogo stimuli following Go cues might be related to increased efforts in activating the response inhibition system thereby interrupting preparations to respond.     

Differential responses to predator cues between two mosquito species breeding in different habitats

1. Natural selection favours females who can correctly assess the predation risk and hence avoid high‐risk oviposition sites and reduce the mortality rate of their offspring. In spite of the potential significance of such behaviour, relatively few studies have assessed the relationship between oviposition behaviour and predation risk. 2. The present study aimed to determine the sublethal effects of predators on oviposition site selection by gravid females, the foraging activity of larvae, and the life history traits of two mosquito species that breed in different habitats, Aedes albopictus Skuse (container breeder) and Culex tritaeniorhynchus Giles (wetland breeder). 3. Female C. tritaeniorhynchus avoided laying eggs at oviposition sites in the presence of a predator cue. In contrast, female A. albopictus laid eggs in both the absence and presence of the predator cue. 4. To examine the effects of predator cues on larval behaviour, experiments were conducted in the absence and presence of a predator cue. Although larval activity was lower in the presence of the predator cue than that in its absence in both species, C. tritaeniorhynchus responded to the predator cue more strongly than A. albopictus. Female A. albopictus that had been reared with caged predators exhibited an extended larval development period, whereas the adult C. tritaeniorhynchus reared in the presence of predators were smaller than those reared in their absence. 5. This finding might explain why C. tritaeniorhynchus avoid laying eggs in predator‐conditioned water, for example to increase the fitness of their offspring, but A. albopictus either cannot detect predator cues or are not sensitive to them.     

Strategy of auditory discrimination of scale in Java sparrows: they use both "imagery" and specific cues

We examined whether Java sparrows use imagery of auditory stimuli (imagery is a subject's mental representation of a stimulus by which the subject's behaviour may be governed under stimulus control even in the absence of the physical stimulus). Three types of ascending tone sequences were used. In the intact scale, sequence tones were played in ascending order. In the intact-masked scale, part of the sequence was masked by noise but the remaining scale was identical with the intact scale, whereas in the violated scale, the sequence could be heard as if tones were played slowly (Experiment 1) or quickly (Experiment 2). Subjects were divided into two groups: one group was trained to respond to the intact and intact-masked scales and to suppress response to the violation scale (imagery-positive group). The contingency was reversed for the other (violation-positive) group. In Experiment 1, all the birds acquired discrimination, but successful transfer to novel stimuli was observed only in the imagery-positive group, suggesting that the imagery of the tone sequence was used as a discriminative cue. Experiment 2 confirmed that the stimulus duration was a discriminative cue for both groups, suggesting that the birds also acquired discrimination using only specific cues.     

Behavioural dissociation between exogenous and endogenous temporal orienting of attention

BACKGROUND: In the current study we compared the effects of temporal orienting of attention based on predictions carried by the intrinsic temporal structure of events (rhythm) and by instructive symbolic cues; and tested the degree of cognitive, strategic control that could be exerted over each type of temporal expectation. The experiments tested whether the distinction between exogenous and endogenous orienting made in spatial attention may extend to the temporal domain. TASK DESIGN AND MAIN RESULTS: In this task, a ball moved across the screen in discrete steps and disappeared temporarily under an occluding band. Participants were required to make a perceptual discrimination on the target upon its reappearance. The regularity of the speed (rhythmic cue) or colour (symbolic cue) of the moving stimulus could predict the exact time at which a target would reappear after a brief occlusion (valid trials) or provide no temporal information (neutral trials). The predictive nature of rhythmic and symbolic cues was manipulated factorially in a symmetrical and orthogonal fashion. To test for the effects of strategic control over temporal orienting based on rhythmic or symbolic cues, participants were instructed either to "attend-to-speed" (rhythm) or "attend-to-colour". Our results indicated that both rhythmic and symbolic (colour) cues speeded reaction times in an independent fashion. However, whilst the rhythmic cueing effects were impervious to instruction, the effects of symbolic cues were contingent on the instruction to attend to colour. FINAL CONCLUSIONS: Taken together, our results provide evidence for the existence of qualitatively separable types of temporal orienting of attention, akin to exogenous and endogenous mechanisms.     

Characterization of the molecular interaction between caveolin-1 and the P2X receptors 4 and 7 in E10 mouse lung alveolar epithelial cells

P2X(4) and P2X(7) receptors are abundantly expressed in alveolar epithelial cells, and are thought to play a role in regulating fluid haemostasis. Here, we analyzed the expression and localization of the P2X(4)R, and characterized the interaction between Cav-1 and both P2X(4)R and P2X(7)R in the mouse alveolar epithelial cell line E10. Using the biotinylation assay, we found that only glycosylated P2X(4)R is exposed at the cell surface. Triton X-100 solubility experiments and sucrose gradient centrifugation revealed that P2X(4)R was partially localized in Cav-1 rich membrane fractions. Cholesterol depletion with Mbeta-CD displaced Cav-1 and P2X(4)R from the low-density to the high-density fractions. Suppression of Cav-1 protein expression using short hairpin RNAs resulted in a large reduction in P2X(4)R levels. Double immunofluorescence showed that P2X(4)R and Cav-1 partially colocalize in vitro. Using the GST pull-down assay, we showed that Cav-1 interacts in vitro with both P2X(4)R and P2X(7)R. Co-immunoprecipitation experiments confirmed the interaction between P2X(7)R and Cav-1. ATP stimulation increased the level of P2X(4)R in the lipid raft/caveolae fraction, whereas Cav-1 content remained constant. Our results support recent evidence that P2X receptors are present in both raft and non-raft compartments of the plasma membrane and thus exhibit variable ATP sensitivity.     

Memory for spatial and object-specific cues in food-storing and non-storing birds

Two storer/non-storer pairs of species, marsh tit (Parus palustris)/blue tit (P. caeruleus) and jay (Garrulus glandarius)/jackdaw (Corvus monedula) were compared on a one-trial associative memory task. In phase I of a trial birds searched for a reward in one of four feeders which differed in their trial-unique spatial location and object-specific cues. Following a retention interval, the birds had to return to the same feeder to obtain a further reward. In control trials the array of feeders was unaltered, whilst in dissociation tests it was transformed to separate spatial location and object-specific cues.In control trials there was no difference in performance between species. In dissociation tests, the two storing species went first to the correct spatial location and second to the correct object-specific cues, whereas the two non-storing species went first with equal probability to the correct spatial and local object cues.Monocular occlusion was used to investigate differences between the two eye-systems. In control trials there was no effect of occlusion. In dissociation trials, all 4 species preferentially returned to the feeder with the correct object-specific cue when the left eye had been covered in phase I and to the feeder in the correct spatial position when the right eye had been covered in phase I.These results suggest that (a) food-storing birds differ from non-storers in responding preferentially to spatial information and (b) in storers and non-storers the right eye system shows a preference for object-specific cues and the left eye system for spatial cues.     

Differential effects of ovarian steroids and triphenylethylene compounds on macromolecular uptake and thymidine incorporation in the mouse uterus

In the rodent uterus, estrogen elicits a biphasic response i.e. an early phase (Phase I) and a late phase (Phase II). Estradiol-17 beta (E2) and estriol (E3), as well as triphenylethylene (TPE) compounds, CI-628 and clomiphene citrate (CC), were used to characterize Phase I and Phase II responses in uterine preparation for implantation in the mouse. While uterine macromolecular uptake (vascular permeability), a Phase I response, was studied in progesterone (P4)-primed animals, uterine [3H]thymidine incorporation (DNA synthesis), a Phase II response, was investigated with and without P4-priming. In the P4-primed uterus, all compounds, except CC, significantly increased uterine macromolecular uptake as determined by interstitial tissue accumulation of [125I]bovine serum albumin [( 125I]BSA). DNA synthesis as determined by cellular incorporation of [3H]thymidine was modulated by P4, estrogens and TPE compounds in a cell-type specific and temporal manner. As a single injection and in the absence of P4, E2 induced [3H]thymidine incorporation in the luminal and glandular epithelium at 18 and 24 h. E3 was inferior to E2 in this response. On the other hand, treatment with P4 for 1 day or 4 days induced [3H]thymidine incorporation primarily in stromal cells. However, stromal cell incorporation was potentiated when P4 treatment was combined with estrogens or TPE compounds. These results reveal the relative importance of Phase I and cell-type specific Phase II responses in uterine preparation for implantation.     

Auditory evoked potentials in Down's syndrome

Short-, middle- and long-latency auditory evoked potentials (SAEPs, MAEPs and LAEPs) were examined in 12 subjects with Down's syndrome and in 12 age-matched normal subjects. In comparison with the normal subjects, Down subjects showed shorter latencies for SAEP peaks II, III, IV and V (and correspondingly shorter interpeak intervals I–II and I–III) so long as stimulus intensity was at least 45 dB SL. The MAEP peak Na had a longer latency in Down subjects than in normal subjects, but not the Pa latency. In passive oddball experiments for LAEPs, the latencies of all components from N1 to P3 were progressively longer in Down subjects, and the N2-P3 amplitude increased slightly between the first and fourth blocks of stimuli (whereas in the normal subjects it decreased). These alterations in auditory evoked potentials, which may correlate with cerebral alterations in organization and responsiveness responsible for deficient information processing, may constitute an electrophysiological pattern that is characteristic of Down's syndrome.     

Chemopreventive and therapeutic modulation of green tea polyphenols on drug metabolizing enzymes in 4-Nitroquinoline 1-oxide induced oral cancer

Oral cancer is one of the most common cancers in the world. Drugs can modulate the expression of drug metabolizing enzymes and are useful in chemoprevention as well as therapy in cancer. 4-Nitroquinoline 1-oxide (4-NQO) is used to induce oral cancer in the present study. In the present investigation, the effect of green tea polyphenols (GTP) on the activities of cytochrome b5, cytochrome P450, cytochrome b5 reductase (cyt b5 R), cytochrome P450 reductase (cyt P450 R), arryl hydrocarbon hydroxylase (AHH), DT-diaphorase (DTD)(Phase I enzymes) and glutathione-S-transferase (GST) and UDP-glucuronyl transferase (UDP-GT) (Phase II enzymes) were assessed in tongue and oral cavity. In induced rats, there was a decrease in the activity of Phase II enzymes and an increase in the activity of Phase I enzymes. On supplementation of GTP by both simultaneous and post treatment mode (200mg/kg) there was a significant increase in the activity of GST and UDP-GT and a significant decrease in the activity of Phase I enzymes. There was a significant decline in the number of tumors, tumor volume and oral squamous cell carcinoma in both simultaneous and post GTP treated animals relative to 4-NQO induced animals; on comparing simultaneous and post GTP treated animals the number of tumors, tumor volume and oral squamous cell carcinoma was significantly reduced in post treated animals. Thus inhibition of Phase I enzymes could be attributed to the protective efficacy of GTP which deactivates carcinogen and GTP induced the expression of Phase II enzymes that detoxifies the 4-NQO. It can be proposed that GTP plays role as a detoxifying agent by which its modulating role prevented/inhibited the formation of tumor.     

Deficits in inhibitory control in smokers during a Go/NoGo task: an investigation using event-related brain potentials

Introduction

The role of inhibitory control in addictive behaviors is highlighted in several models of addictive behaviors. Although reduced inhibitory control has been observed in addictive behaviors, it is inconclusive whether this is evident in smokers. Furthermore, it has been proposed that drug abuse individuals with poor response inhibition may experience greater difficulties not consuming substances in the presence of drug cues. The major aim of the current study was to provide electrophysiological evidence for reduced inhibitory control in smokers and to investigate whether this is more pronounced during smoking cue exposure.

Methods

Participants (19 smokers and 20 non-smoking controls) performed a smoking Go/NoGo task. Behavioral accuracy and amplitudes of the N2 and P3 event-related potential (ERP), both reflecting aspects of response inhibition, were the main variables of interest.

Results

Reduced NoGo N2 amplitudes in smokers relative to controls were accompanied by decreased task performance, whereas no differences between groups were found in P3 amplitudes. This was found to represent a general lack of inhibition in smokers, and not dependent on the presence of smoking cues.

Conclusions

The current results suggest that smokers have difficulties with response inhibition, which is an important finding that eventually can be implemented in smoking cessation programs. More research is needed to clarify the exact role of cue exposure on response inhibition.     

An Arg307 to Gln polymorphism within the ATP-binding site causes loss of function of the human P2X7 receptor

The P2X(7) receptor is a ligand-gated channel that is highly expressed on mononuclear cells of the immune system and that mediates ATP-induced apoptosis. Wide variations in the function of the P2X receptor have been observed, explained in part by (7)loss-of-function polymorphisms that change Glu(496) to Ala (E496A) and Ile(568) to Asn (I568N). In this study, a third polymorphism, which substitutes an uncharged glutamine for the highly positively charged Arg(307) (R307Q), has been found in heterozygous dosage in 12 of 420 subjects studied. P2X(7) function was measured by ATP-induced fluxes of Rb(+), Ba(2+), and ethidium(+) into peripheral blood monocytes or various lymphocyte subsets and was either absent or markedly decreased. Transfection experiments showed that P2X(7) carrying the R307Q mutation lacked either channel or pore function despite robust protein synthesis and surface expression of the receptor. The monoclonal antibody (clone L4) that binds to the extracellular domain of wild type P2X(7) and blocks P2X(7) function failed to bind to the R307Q mutant receptor. Differentiation of monocytes to macrophages up-regulated P2X(7) function in cells heterozygous for the R307Q to a value 10-40% of that for wild type macrophages. However, macrophages from a subject who was double heterozygous for R307Q/I568N remained totally non-functional for P2X(7), and lymphocytes from the same subject also lacked ATP-stimulated phospholipase D activity. These data identify a third loss-of-function polymorphism affecting the human P2X(7) receptor, and since the affected Arg(307) is homologous to those amino acids essential for ATP binding to P2X(1) and P2X(2), it is likely that this polymorphism abolishes the binding of ATP to the extracellular domain of P2X(7).     

Hummingbird avoidance of nectar-robbed plants: spatial location or visual cues

Broad-tailed and rufous hummingbirds avoid plants and flowers that have recently been visited by nectar-robbing bees. However, the cues the hummingbirds use to make such choices are not known. To determine the proximate cues hummingbirds use to avoid visiting nectar-robbed plants, I conducted multiple field experiments and one aviary study using the nectar-robbed, hummingbird-pollinated plant Ipomopsis aggregata . In the first field experiment, free-flying hummingbirds were presented with plants in which I manipulated nectar volume and the presence of nectar-robber holes. Hummingbirds visited significantly more plants with nectar and probed more available flowers on those plants, regardless of the presence of nectar-robber holes. Thus, I hypothesized that hummingbirds may avoid robbed plants based on their spatial memory of unrewarding plants and/or visual cues that nectar absence provides. In an aviary study, I removed spatial cues by re-randomizing the position of plants after each hummingbird-foraging bout, but hummingbirds still selected plants with nectar. Nectar may provide a visual cue in I. aggregata flowers because corollas are translucent, and nectar is visible through the side of the corolla. To determine if hummingbirds use this visual cue to avoid plants with no nectar, I masked corolla translucence in a field study by painting flowers with acrylic paint. Hummingbirds still visited significantly more plants with nectar and probed more flowers on those plants, whether or not the corollas were painted. These results suggest that hummingbirds use nectar as a proximate cue to locate and avoid non-rewarding, nectar-robbed plants, even in the absence of spatial cues and simple visual cues.