Effect of visual background complexity and light level on the detection of visual signals of male <Emphasis Type="Italic">Schizocosa ocreata</Emphasis> wolf spiders by female conspecifics

For visual signaling to be effective, animal signals must be detected and discriminated by receivers, often against complex visual backgrounds with varying light levels. Accordingly, in many species, conspicuous visual displays and ornaments have evolved as a means to enhance background contrast and thereby increase the detection and discrimination of male courtship signals by females. Using video playbacks, we tested the hypothesis that visual courtship displays and leg decorations of male Schizocosa ocreata wolf spiders are more conspicuous against complex leaf-litter backgrounds. Video exemplars of courting males with manipulated leg tufts were superimposed on different backgrounds (complex leaf litter in sun or shade, featureless gray background) and presented to female spiders. Females were more likely to orient to males presented against lighter backgrounds (litter in sun, gray) than the darker ones (litter—shade). Males with larger tufts were also more likely to be detected, as latency to orient was shortest for enlarged and longest for removed tufts. Latency of females to approach was shorter against lighter backgrounds, and approach latency was longest for males without tufts. Female receptivity scores were significantly greater for males against lighter backgrounds, and males with larger tufts had higher scores. These results suggest that both complexity and light level of display backgrounds affect the detection of male visual courtship signals by females and that aspects of the male phenotype may increase chances of detection (and receptivity) against visually complex backgrounds.     

Experience with chemotactile cues indicating female feeding history impacts male courtship investment in the wolf spider <Emphasis Type="BoldItalic">Schizocosa ocreata</Emphasis>

Male fitness is often determined by the ability of the male to gain access to multiple mates, although in species that exhibit sexual cannibalism, males might increase their likelihood of being cannibalized with each encounter. This risk should create selection for males who are able to perceive potential risks associated with mating encounters. We studied male Schizocosa ocreata wolf spiders to determine whether they use female chemotactile cues (silk, excreta) as indicators of potential risks and how these cues affected subsequent male courtship behaviors. Female treatments included satiated females vs. starved females, as well as a treatment where females had recently cannibalized a male S. ocreata. We performed experiments to assess (1) if males use female chemotactile cues to determine potential risks associated with differing female feeding treatments and alter courtship investment, and 2) how male experience with female chemotactile cues affected courtship investment in subsequent female encounters. At first encounter, males do not vary courtship investment (number of bouts, duration, and vigor) with different female feeding treatments. However, male behaviors during subsequent encounters with female chemotactile cues varied in complex ways, depending on female feeding treatment and male first encounter experience. These data suggest that male experience impacts perception of female chemical cues and offers the male opportunity to avoid sexual cannibalism in high-risk situations.     

Sexual selection,male morphology,and the efficacy of courtship signalling in two wolf spiders (Araneae: Lycosidae)

Males of the brush-legged wolf spider, Schizocosa ocreata (Araneae: Lycosidae), possess a conspicuous male secondary sexual character: dark pigmentation and tufts of bristles on the tibiae of their forelegs. We tested several hypotheses relating to the role of this conspicuous trait in sexual selection. Triad mating experiments suggest that the tufts do not play an obvious role in the operation of sexual selection by either male competition or female choice, as there were no significant differences in the mating success of intact and experimentally shaved males. However, females mated more often with males that initiated courtship first, suggesting that capture of a female’s attention by male signalling may play a critical role. In behavioral experiments that paired a single male with a female in arenas that allowed both visual and vibratory signal transmission during courtship, female receptivity did not vary significantly with the presence or absence of tufts. However, experiments that isolated the visual component of communication (by eliminating vibratory communication) revealed a significant effect of the presence of tufts: females showed receptivity less often to males with tufts removed. Female response to visual signals was much greater in S. ocreata than in its sibling congener, Schizocosa rovneri, which lacks male tufts. We hypothesize that the tufts serve to increase the efficacy of visual displays of S. ocreata, as vibratory communication is constrained by the complex leaf litter habitat of some populations. Such environmental constraints may make visual signalling over distance a critical factor for effective courtship communication, which may in turn strongly influence male fitness. Received: 30 September 1994/Accepted after revision: 4 August 1995     

Limb regeneration and subsequent asymmetry in a male secondary sexual character influences sexual selection in wolf spiders

Males of the brush-legged wolf spider Schizocosa ocreata (Hentz) have conspicuously decorated forelegs used in courtship and agonistic displays. Approximately one in five juvenile males has a missing or regenerating foreleg, and regeneration of a leg lost during development usually results in the absence of a decorative tuft on that leg. The subsequent asymmetry in this male secondary character significantly decreases success in both courtship of females and male-male agonistic interactions. Experimental removal of tufts from one leg of previously successful symmetric males produces similar results. As a test for concomitant behavioral effects, female spiders were shown video images of a courting male with symmetric tufts and the same video image altered to have asymmetric tufts. Female receptivity to the asymmetric video image was lower. In contrast to fluctuating asymmetry resulting from developmental instability, leg tuft asymmetry in S. ocreata most likely arises from a single event during ontogeny – possibly leg loss from an aggressive or predator encounter  – and may serve as a quality indicator in female mate choice. Received: 27 July 1995/ Accepted after revision: 19 November 1995     

Light environment and mating behavior in Trinidadian guppies (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>)

Male guppies, Poecilia reticulata, have color patterns that result from a balance between natural selection for crypsis to avoid predators and sexual selection for bright, complex patterns that attract females. Males use displays to show off these patterns to potential mates, but their conspicuousness also depends on the light environment in which they are viewed. We investigated variation in natural underwater guppy light environments in Trinidad, West Indies, and found that mating behavior is correlated with both the ‘quantity’ (total irradiance) and ‘quality’ (spectral composition) of light: light intensity and the proportion of ultraviolet light were negatively related to display rates. Experimental manipulation of light environment to mimic natural daily changes demonstrated that these relationships are causal and are independent of time of day effects. At lower light levels, when guppies are less detectable by visually hunting predators, females had more opportunity for active mate choice, because males displayed more. However, these light conditions may reduce the ability of females to accurately discriminate between males. Guppy mating behavior is therefore strongly affected by light environment, and this may have important effects on sexual selection.     

Love bites: male fang use during coercive mating in wolf spiders

Evolutionary conflicts of interest between the sexes are common, as mating tactics and strategies that increase fitness benefits for one sex may incur costs for the other. As a consequence, antagonistic coevolution between the sexes often results in a complex arms race between male persistence and female resistance. Coercive mating (e.g., forced copulation) likely benefits males by increasing the probability of mating; however, costs to females may be high, including injury or even death. Here, we report on a study of the use of fangs by males of the wolf spider Schizocosa ocreata (Hentz) during forcible mating with resistant females, which results in hemolymph loss and scar tissue formation in females. Microscopic inspection revealed that fang wounds (evidenced by scar tissue) were absent on unmated (virgin) females but were found on mated females and were significantly more frequent in coercively mated females. Experimental fang immobilization studies found no difference in copulation success between experimental (fangs immobilized) and control (sham manipulation) males. However, males that had use of their fangs had significantly longer copulation duration. These findings represent a previously unknown male mating tactic in spiders and an unrecognized potential cost of mating for female spiders.     

Asymmetry in a visual signaling character and sexual selection in a wolf spider

Fluctuating asymmetry (FA) can indicate developmental instability in bilaterally symmetric organisms, and studies have shown that the degree of asymmetry in male secondary sexual characters influences female mate choice in a number of taxa. In male Schizocosa ocreata wolf spiders, conspicuous tufts of bristles on the forelegs are a critical component of visual courtship signals, which appear to play a role in female mate choice. Previous studies have shown that females exhibit reduced receptivity to males with regenerative asymmetry, a consequence of leg loss and regeneration that causes males to be grossly asymmetric with respect to this important signaling character. We provide data on the occurrence of FA in the tufts of S. ocreata, and examine further the influence of asymmetry on female mate choice. The distribution of tuft area asymmetry values from a sample of field-collected males was normal, with a mean value of zero, indicating true FA. For a subset of males measured directly after field collection and prior to feeding, tuft asymmetry was significantly negatively correlated with measures of body size (body length) and condition (abdomen volume/cephalothorax width). Receptivity responses of females to visual signals from live males of similar size varied with the degree of asymmetry in male tufts. Since FA covaries with male body size and condition, which may also influence behavioral vigor, we used video image manipulation to alter the degree of asymmetry in tufts of a courting male while holding size and condition constant. Asymmetry treatments represented values within the range of natural FA variation as well as more extreme values characteristic of regenerative asymmetry. With the confounding effects of male size, condition, and behavior held constant, female spiders exhibited reduced receptivity responses to all experimental asymmetric video images relative to a control video stimulus. There were no differences in the frequency of female receptivity among the various asymmetry treatments, suggesting that discrimination against asymmetry in conspecific male signal characters is not simply a rejection of extreme phenotypes. Results suggest that asymmetry in a key male secondary character used in visual signaling, independent of any concomitant behavioral or size factor, is an important criterion in mate choice. Received: 26 February 1998 / Accepted after revision: 12 September 1998     

Chemosensory cues allow male lizards<Emphasis Type="Italic"> Psammodromus algirus</Emphasis> to override visual concealment of sexual identity by satellite males

Males of many species of lizards show conspicuous breeding colors but, in some species, young competitively inferior males conceal their sexual identity by a female-like dull coloration that allows them to evade aggression from dominant males and to adopt an alternative satellite-sneaking mating tactic. However, large males of the lizard Psammodromus algirus reacted aggressively to young intruder males despite their female-like coloration, suggesting that they might have the ability to recognize competitor males by chemosensory cues. We experimentally manipulated the head coloration (brown vs orange) and scents (male vs female) of small young males. For staged agonistic encounters, we compared the response of resident unmanipulated large males to the different manipulated small males. When we manipulated only the color of small males, the response of resident large males was independent of the paint manipulation; brown and orange males elicited a similar aggressive response. However, when we also manipulated the scent, small males painted orange or brown, but bearing the scent of males, received a significantly higher number of aggressive responses than small males painted orange or brown, but bearing the scent of females. The results showed that, at close range, the reaction of large males to manipulated individuals was dependent on the scent, whereas color seemed to be less important. Coloration may be, however, more important in long-distance communication as shown by the outcome of the first encounters. Also, orange coloration may increase the intensity of the aggressive response. Effective sex recognition by territorial large males is important in natural situations to avoid sneak matings by young male competitors. Thus, even if small males visually conceal their sexual identity, chemosensory cues allow large males to identify them at close range.     

Color patterns of the shrimps Heptacarpus pictus and H. paludicola (Caridea: Hippolytidae)

Color patterns of the shallow-water shrimps Heptacarpus pictus and H. paludicola are formed by chromatosomes (usually termed chromatophores) located beneath the translucent exoskeleton. Development of color patterns is related to size (age) and sex. The color expressed is determined by the chromatosome pigment dispersion, arrangement, and density. In populations with well-developed coloration (H. pictus from Cayucos, California, 1976–1978, H. paludicola from Argyle Channel, San Juan Island, Washington, June–July, 1978), prominent coloration was a characteristic of maturing females, breeding females, and some of the larger males. In the Morro Bay, California, population of H. paludicola (sampled 1976–1978), color patterns were poorly developed except in a few large females. In both species, most shrimp lose color at night because of pigment retraction in certain chromatosomes. In both species, there are 5 basic morphs: 1 transparent and 4 colored morphs. In the colored morphs, the color patterns are composed of bands, stripes, and spots which appear to disrupt the body outline. Each color morph also has a common environmental color in its color pattern, e.g the green of green algae, the whites and pinks of dead and living coralline algae, and various shades of tidepool litter. These shrimps are apparently under heavy predation pressure by fish, and it is suggested that the color patterns are camouflage against such visually-hunting predators.     

Costs of reproduction in lizards: escape tactics and susceptibility to predation

Summary Increased basking and reduced agility in gravid female southern water skinks (Eulamprus tympanum) suggest that they will be more vulnerable to predators. However, gravid females shift their anti-predator tactics towards crypsis, by allowing potential predators (such as a human observer) to approach more closely than do males and non-gravid females. Gravid females were taken no more frequently than were non-gravid females or males when exposed to two types of natural predators, birds (kookaburra, Dacelo gigas) or snakes (common blacksnakes, Pseudechis porphyriacus) in field enclosures. Both these results suggest that the vulnerability of potential prey in this system is determined by the predator's probability of detecting a potential prey item, not its probability of capturing the prey item after detection. Hence, laboratory-based measures of performance demonstrating reduced escape speed may sometimes have little relevance to actual fitness under field conditions, if the probability that an animal will be taken by a predator depends primarily on whether or not it is seen, rather than on how quickly it can escape. Correspondence to: L. Schwarzkopf     

Daring females,devoted males,and reversed sexual size dimorphism in the sand-dwelling spider <Emphasis Type="Italic">Allocosa brasiliensis</Emphasis> (Araneae,Lycosidae)

Sexual selection theory predicts that a higher investment in offspring will turn females into the selective sex, while males will compete for accessing and courting them. However, there are exceptions to the rule. When males present a high reproductive investment, sex roles can reverse from typical patterns, turning males into the choosy sex, while females locate males and initiate courtship. In many spiders, males are smaller than females, wandering in search of sedentary females and maximizing the number of copulations. In the present study, we present findings on the sand-dwelling wolf spider, Allocosa brasiliensis, evidencing a reversal in typical courtship roles reported for the first time in spiders. Males were bigger than females. Females located males and initiated courtship. Copulation always occurred in male burrows and took place mainly in long burrows. Males donated their burrows to the females after copulation, closing the entrance before leaving with female cooperation from inside. Males would provide females with a secure place for ovipositing, being exposed to predation and diminishing their future mating possibilities until constructing a new burrow. The cost of vacating the burrow and losing the refuge in an unpredictable habitat, such as sand dunes, would explain the courtship roles reversal in this spider species. Results turn A. brasiliensis as a promising model for discussing the determinants of sex roles and the pressures that drive their evolution and maintenance. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Condition dependence of male display coloration in a jumping spider (Habronattus pyrrithrix)

In many animals, conspicuous coloration functions as a quality signal. Indicator models predict that such colors should be variable and condition dependent. In Habronattus pyrrithrix jumping spiders, females are inconspicuously colored, while males display brilliant red faces, green legs, and white pedipalps during courtship. We tested the predictions of the indicator model in a field study and found that male body condition was positively correlated with the size, hue, and red chroma of a male’s facial patch and negatively correlated with the brightness of his green legs. These traits were more condition dependent than non-display colors. We then tested a dietary mechanism for condition dependence using two experiments. To understand how juvenile diet affects the development of coloration, we reared juvenile spiders on high- and low-quality diets and measured coloration at maturity. To understand how adult diet affects the maintenance of coloration, we fed wild-caught adults with high- or low-quality diets and compared their coloration after 45 days. In the first experiment, males fed high-quality diet had redder faces, suggesting that condition dependence is mediated by juvenile diet. In the second experiment, red coloration did not differ between treatments, suggesting that adult diet is not important for maintaining the color after it is produced at maturity. Diet had no effect on green coloration in either experiment. Our results show different degrees of condition dependence for male display colors. Because red is dependent on juvenile diet, it may signal health or foraging ability. We discuss evidence that green coloration is age dependent and alternatives to indicator models for colorful displays in jumping spiders.     

Interacting effects of ambient light and plumage color patterns in displaying Wire-tailed Manakins (Aves,Pipridae)

Sending color signals to conspecifics may attract predators, leading to opposing selection pressures on the evolution of signal expression and display behavior in animals. The costs of signaling can be reduced, however, because conspicuousness is the combined result of the reflectance spectra of the displayer's color pattern and the spectra of ambient light illuminating the animal. Changes in ambient light can alter conspicuousness, even when chemical and structural color-generating mechanisms remain constant, potentially allowing animals to display their colors most fully in light environments where the benefits are greatest relative to the costs. Using spectroradiometric methods, we determined how light habitat use affects conspicuousness in adult males of the Wire-tailed Manakin Pipra filicauda, a lekking bird species with vivid plumage colors. We studied three aspects of visibility, including properties of the entire color pattern, visual contrast within an individual's plumage and a bird's contrast relative to its visual background. Wire-tailed Manakins usually displayed in forest shade environments, which reduced their conspicuousness at larger viewing distances, while maximizing visual contrast within the plumage color pattern at close viewing distances. Compared to sunspots, ambient light in forest shade reduces the contrast of individual bird colors with the background at close viewing distance. However, background contrast of individual bird colors in the shade was still relatively higher during sunny than during cloudy weather which may explain why males were more active when the sun was not blocked by clouds. Assuming that the visual perceptions of predators and other manakins do not differ from the reflectance patterns we measured, Wire-tailed manakins tend to display in light environments that reduce the conflicts between avoiding long distance detection by predators and displaying conspicuous color signals to visiting females.     

Crypsis versus intimidation—anti-predation defence in three closely related butterflies

Butterflies that hibernate exhibit particularly efficient defence against predation. A first line of defence is crypsis, and most hibernating butterflies are leaf mimics. When discovered, some species have a second line of defence; the peacock, I. io, when attacked by a predator flicks its wings open exposing large eyespots and performs an intimidating threat display. Here we test the hypothesis that butterflies relying solely on leaf mimicking and butterflies with an intimidating wing pattern, when attacked, exhibit different behavioural suites—because leaf mimicking is best implemented by immobility, whereas intimidating coloration is best implemented by intimidating behaviour. In laboratory experiments blue tits, Parus caeruleus, were allowed 40 min to attack single individuals of three species of butterfly: one relying solely on crypsis, the comma, Polygonia c-album; one relying on intimidating wing pattern in addition to crypsis, the peacock; and one intermediate species, the small tortoiseshell Aglais urticae. The results are in accordance with expectations and demonstrate that: (1) birds take longer to discover the leaf mimicking species, the comma, than the tortoiseshell and the peacock; (2) the comma remained motionless throughout experimental trials but small tortoiseshells and peacocks flicked their wings when attacked; (3) the most intimidating butterfly, the peacock, started flicking its wings at a greater distance from the attacking bird than the small tortoiseshell; and (4) the intimidating pattern and behaviour of peacocks was effective—when discovered, all peacocks survived interactions with blue tits, whereas only 22% of commas and 8% of small tortoiseshells survived.     

Background and temperature effects on Uca panacea color change

Organismal coloration is used for communication, camouflage, and thermoregulation. These functions of body coloration may impose conflicting demands upon color-changing organisms. Here, we examined interacting thermoregulatory and camouflage color change responses when fiddler crabs Uca panacea were subject to simultaneously changing temperatures (10, 25, 40 °C) and backgrounds (black, white). Crab coloration lightened on a white background and at high temperatures and darkened on a black background and at low temperatures, reflecting the camouflage and thermoregulatory functions of color change. Synergistic background and temperature treatments (i.e., hot/white or cold/black) induced strong color change responses. When temperature and background were in conflict (i.e., hot/black or cold/white), responses to background coloration constrained thermoregulatory color change such that carapace coloration did not change. Such conflicts are likely to be common in nature, especially in highly heterogeneous environments. Throughout the experiment, males remained lighter than females and showed a greater response to the hot/white treatment, driven by a stronger response to high temperatures. These differences may reflect the physiological, morphological, and behavioral differences associated with sexual selection and sexual dimorphism in this species.     

Conspicuous displays in cryptic males of a polytypic poison-dart frog

The evolution of aposematism is linked to increased opportunities for conspicuous sexual displays since detection by potential predators is no longer disadvantageous. Therefore, phenotypic divergence in aposematic species leading to relatively cryptic forms is expected to constrain such opportunities, by restoring the trade-off between natural and sexual selection on the boldness of sexual displays. We asked if and how a derived phenotype of the poison-dart frog Oophaga granulifera that appears relatively cryptic to potential predators exhibits conspicuous sexual displays for potential mates. We used visual modeling of frog contrasts against their natural backgrounds to test if for conspecifics green frogs appear less conspicuous than red frogs as they do for birds. We conducted behavioral observations of focal red and green males to determine if green frogs adjust their display behavior to the availability of potential mates. Dorsal brightness is known to influence female preferences in at least one poison frog species. We found that, despite being less visible under some measures, green frogs may appear as bright as red frogs for conspecifics but not birds, when viewed on dark backgrounds. Additionally, green males called more intermittently than red males when advertising to distant females, but they exhibited a dramatic increase in calling activity in proximity of a female and were as active as red males in this context. Together, our results suggest that green frogs retain context-dependent conspicuousness to conspecifics despite the evolution of relative crypsis to potential predators.     

Elytra color as a signal of chemical defense in the Asian ladybird beetle Harmonia axyridis

Carotenoid- and melanin-based colors are valuable indicators of quality in many vertebrates, but their signaling role in invertebrates remains relatively unexplored. The Asian ladybird beetle Harmonia axyridis is an ideal organism for studies of this nature because males and females exhibit highly variable red and black colors on their elytra and are chemically defended with an alkaloid (harmonine). We used digital photography to quantify elytra coloration and absorbance spectrophotometry and gas chromatography mass spectrometry analyses to quantify pigment and alkaloid concentrations, respectively, in wild-caught male and female H. axyridis. We predicted that extensive or intense coloration would be an aposematic signal of high-alkaloid stores. We found that carotenoid pigments largely controlled variation in red elytra coloration. There was no relationship between alkaloid content and either elytra redness or carotenoid pigment concentration in either sex. However, we found a positive correlation between the extent of elytra coloration and alkaloid content. Animals with proportionally more red (or less black) on the elytra were more alkaloid-rich; this relationship was particularly strong in females. We also found that females with lighter black spots had greater amounts of harmonine than those with darker spots. These results suggest that elytra color patterns have the potential to reveal information about chemical defensiveness to mates or predators. Prior studies in this species show that nonmelanic forms are typically less active and yet more sexually attractive than melanic forms, and both results may be explained by the fact that nonmelanics are better chemically defended.     

Preference for male traits in female wolf spiders varies with the choice of available males,female age and reproductive state

Individual variation in female preference for male traits may influence mate choice, especially if benefits and costs of choosiness vary with the range of available males or reproductive timing. We examined variation in female preference for male leg tuft size in Schizocosa ocreata (Hentz) wolf spiders with video playback. Dichotomous (simultaneous) choice test experiments included all possible combinations of four stimuli (i.e., modified versions of the same video male stimulus): average tuft size (control), reduced (−25%), enlarged (+25%), and no tufts (removed). Females exhibited a directional preference for larger tuft size independent of the nature of the choice (except for reduced tufts vs no tufts where no difference was seen). Female preference in the short term (over a period of 4 days) was also highly repeatable for control vs reduced tufts, but not for control vs enlarged tufts. Responses of females in ‘no-choice’ presentations of a single (control) male stimulus varied with age post-maturity; females were less receptive in weeks 1 and 2, highly receptive at week 3, and less thereafter. Mated females were least receptive and most aggressive towards a male stimulus. Females offered choices repeatedly at different ages post-maturity consistently preferred the control male vs reduced tufts over all 3 weeks but varied in their preference for enlarged tufts vs control male. In the first 2 weeks, females preferred the enlarged tuft male stimulus, but showed no preference by the third week. Females tested in week 4 showed no preference in either choice. Results suggest that the potential interaction between female preference for male traits and female reproductive timing may be a critical consideration in mate choice.     

Male signaling behavior and sexual selection in a wolf spider (Araneae: Lycosidae): a test for dual functions

Male signaling behaviors are often studied in a single context but may serve multiple functions (e.g., in male–male competition and female mate choice). We examined the issue of dual function male signals in a wolf spider species Schizocosa ocreata (Hentz) that displays the same species-specific signaling behaviors in both male–male and male–female contexts. These signaling behaviors have been described as either aggression or courtship according to the context observed. We tested the possibility of dual functions by comparing the relationship between behaviors and outcome of male–male contests (winner/loser) and male–female mating encounters (mating success). Frequency, rate, and mean duration of signaling behaviors did not vary with outcome of male–male contests, which appears instead to be based upon relative size and body mass. Winners of contests had significantly greater body mass than losers, and greater mass relative to opponents was significantly associated with probability of winning. Overall, signaling rates were much higher in male–female interactions than in male–male contests and were higher for males that successfully mated than for those that did not mate. Mean duration of some male displays was also greater for males that successfully mated. However, male size was not associated with probability of mating. Taken together, results suggest an intersexual selection context for the current function of male signals in these wolf spiders and that increased display vigor is associated with male mating success.     

Coloration in New World orioles

Summary Although sexual dichromatism in birds is usually ascribed to sexual selection, some workers argue that avian coloration is better explained by predation-related selection pressures. Supporting evidence for these latter hypotheses comes primarily from broad interspecific comparisons, which can be biased by a variety of factors. This study examines the predation-based hypotheses of Baker and Parker (1979), particularly the Predator Deflection Hypothesis, with reference to two closely-related oriole species: Icterus parisorum, which is dichromatic, and I. gularis, in which both sexes are brightly coloured. To test the prediction that bright coloration serves to divert the attention of predators away from cryptic young, rates of predation on nests of conspicuous (2 years of age or older) and dull-coloured (first-year). I. parisorum males were compared. The results showed equal predation on the young of males in both age/plumage classes. The Predator Deflection Hypothesis also predicts that, once a predator has been detected, brightly-coloured birds should attempt to distract it, whereas cryptic individuals should not. Tests using models of avian predators showed that this was not the case: cryptic I. parisorum females responded as aggressively toward the model as did conspicuous conspecific males. The same was true for I. gularis. Overall, the results did not support the idea that bright coloration has evolved in response to predation pressure in these species.