Bright Males Research Articles

Changes in expression and honesty of sexual signalling over the reproductive lifetime of sticklebacks.

Fitness costs of signalling are essential in order for reliable sexual signalling to prevail when the interests of the sexes conflict. This means that signalling can be subjected to a life history trade-off between present and future signalling effort. Here, I show that three-spined stickleback males (Gasterosteus aculeatus), who have a single breeding season during which they breed repeatedly, change their red nuptial coloration over the season depending on their body size at the start of breeding. Large males that completed several breeding cycles increased their red coloration over the season, whereas small males, who completed only a few cycles, did not. The increase in coloration was accompanied by an increase in parental success when males were energy constrained, but not when they had access to an unlimited food supply. Red coloration was thus an honest signal of male parental ability despite changes in signal expression when both signalling and parental care were costly and the investments in them changed simultaneously over the reproductive lifetime. However, the honesty of the signal varied over a lifetime. At the penultimate cycle, bright males cannibalized some of their eggs, probably to increase survival to the last cycle, whereas males cared for their offspring independent of coloration at the ultimate cycle.

Carotenoid-based ornamentation and status signaling in the house finch

The status signaling hypothesis (SSH) was devised primarily to explain the adaptive significance of avian ornamental coloration during the nonbreeding season. It proposes that conspicuous male plumage serves as an honest signal of social status within a population of birds. However, to date this hypothesis has been well tested and supported for only one type of plumage coloration, melanin-based coloration. Carotenoid-based pigmentation is known to positively reveal male health and condition during molt in a variety of species, but it is poorly understood whether this ornament type can also function as a status signal during the winter. We tested the SSH in male house finches (Carpodacus mexicanus) by manipulating the carotenoid-based plumage brightness of first-year males and then pairing unfamiliar birds of differing coloration in a series of dominance trials in captivity. Manipulated plumage color was unrelated to win/loss outcome in these trials. Similarly, the natural pigmentation of males was a poor predictor of winter dominance; as in other studies with this species, we found only a weak tendency for naturally drab males to dominate naturally bright males. These results suggest that carotenoid-based coloration is not a reliable indicator of social status in male house finches during the nonbreeding season. In fact, carotenoid-based coloration may function only in mate choice in this species, and it may be retained throughout the year either because time constraints preclude a second plumage molt or because it aids in pair formation that begins in late winter.

Courtship displays and coloration as indicators of safety rather than of male quality : the safety assurance hyposthesis

Male courtship displays and bright coloration are usually assumed to provide information to females about some aspect of the male’s value as a mate. However, in some species, courtship may serve another function—namely, indicating the current predation risk at the mating site and assuring the female that it is safe to mate there at this time. We developed this safety assurance hypothesis (SAH) and tested its predictions in the bluehead wrasse (Thalassoma bifasciatum), a Caribbean reef fish. Females in this species come to males’ territories to spawn, and males court each arriving female. Males with larger white flank patches court less intensely than less bright males. We show that such males are probably more visible to predators and thus need not court so intensely to provide the same degree of safety assurance to a female. When model lizardfish predators are presented at spawning sites, males habituate to them quickly, but newly arriving females who see the predator are expected to demand more assurance of site safety. Accordingly, and consistent with the SAH, males court females more intensely (longer average courtship bout length) under such circumstances, but males with bright flank patches do not increase their courtship as much as duller males do. Despite this relatively low intensity of courtship, the spawning rate of bright males does not decline relative to that of duller males in the presence of a predator, suggesting that bright coloration conveys a differential benefit. Females of species like the bluehead wrasse, who spawn repeatedly over the course of their life, are expected to be more concerned with their own risk of mortality during each spawning bout than with the quality of a particular male. It is in such species that we expect the SAH to be most applicable. Key words: bluehead wrasse, coral reefs, courtship behavior, fish, risk aversion, safety, Thalassoma bifasciatum. [Behav Ecol 11:444–451 (2000)]

Plumage Brightness and Breeding-Season Dominance in the House Finch: A Negatively Correlated Handicap?

Abstract A variety of observations indicate that the carotenoid-based coloration of male House Finches (Carpodacus mexicanus) is an honest signal of quality. Plumage redness in this species positively reveals male nutritional condition, over-winter survival, and nest attentiveness. As a result, in the breeding season, male House Finches with brighter ornamental plumage are preferred by females as social mates over males with drabber plumage. In the nonbreeding season, however, bright red plumage does not seem to confer an advantage in aggressive interactions, as males with drabber plumage tend to dominate males with brighter plumage. We investigated this apparent paradox by conducting a breeding-season dominance experiment using captive males. We paired unfamiliar males of contrasting plumage brightness in a series of dominance trials during the breeding season and found that drabber males were dominant to brighter males in competition for access to food. Furthermore, in two captive flocks of males, plumage brightness was significantly negatively associated with social dominance. Although we have no conclusive evidence to explain why drab male House Finches are dominant to bright males throughout the year, we believe that motivational asymmetry may contribute to the observed negative correlation between signal intensity and signaler quality (“negatively correlated handicap”). Drab males may be more willing to compete for access to food or to females than are bright males because of the nutritional and/or mating disadvantages from which they suffer.

Plumage brightness in relation to haematozoan infections in the greenfinch Carduelis chloris: Bright males are a good bet

Variation in plumage brightness (yellowness) and prevalence and intensity of haematozoan infections in greenfinches Carduelis chloris L. were studied in three populations, widely separated in geographic location from Spain to Finland. Sexual dichromatism (SD) in coloration was marked, males being yellower than females. Although older birds were generally yellower than younger birds, the degree of SD in coloration increased with age, perhaps due to delayed plumage maturation in males. The prevalence of haematozoan infections was unrelated to any measure of male plumage coloration, but the intensity of haematozoan infections was strongly negatively related to male plumage brightness, and this pattern was similar in all three populations. Hence, male plumage brightness reveals information about the extent to which males are parasitized. This result is in accordance with the Hamilton-Zuk hypothesis, which suggests that bright male plumage has evolved to indicate heritable resistance to parasites. The fact that lightly-infected males had brighter plumage than non-infected and heavily infected ones may suggest that non-infected males were a mixture of both susceptible and resistant individuals, whereas lightly infected individuals might have been effectively immune to parasites. Our data provide a clear example of the negative association between plumage brightness and blood parasite loads in birds, and suggest that male plumage yellowness in the greenfinch can function as an indicator of male quality.

Mutual mate choice in sticklebacks: attractive males choose big females, which lay big eggs

Brighter red three-spined stickleback,Gasterosteus aculeatus, males have been shown to be preferred by females in the laboratory but in the field, these males did not receive more eggs. Instead, they had heavier eggs in their brood. We investigated the hypothesis that sexual selection for red coloration in male sticklebacks acts through mate choice by preferred males, who can afford to be choosy, for high-quality females which lay heavier eggs. We assume here that heavier eggs provide a direct fitness advantage. In simultaneous choice tests males were presented with two females differing in size. The number of zigzags directed to and the time spent orienting to each female were measured. After the test the females laid eggs, which we counted and weighed. Bigger (i.e. longer and heavier) females laid significantly more and heavier eggs than smaller females. For all 23 males pooled together, the preferred female was the bigger of the two in 17 cases, laid more eggs in 18 cases, but laid heavier eggs in only 13 cases. When bright and dull males were analysed separately, we found that bright but not dull males spent more time oriented to the bigger female, and to the female that laid more eggs. Females preferred by bright males tended to lay heavier eggs than nonpreferred females, although this result was not quite significant. We conclude that in nature this preference for bigger females results in brighter males receiving on average heavier eggs. Assuming higher survival of bigger offspring, we propose that this can explain how brightness can be sexually selected in spite of brighter males not receiving more eggs.

The role of bright plumage in male–male interactions in the ring-necked pheasant

The brightness and colour of birds’ plumages have been considered sexually selected traits, indicating health, condition or parasite resistance. However, recent studies with pheasants,Phasianus colchicussuggest they are not signals used by females in mate choice. Instead, males might rely on plumage when assessing the quality of competitors. In this study, bright and experimentally dulled males were presented to a group of captive male pheasants to determine the response to differences in plumage brightness of the intruder. Males in the group directed more aggression to the experimentally dulled males than they did to any other males. This may be partly because they considered the dull males as novel males. When the bright and the dull males were both unknown, both still received more aggression than the average for any individual in the group, but dull males were attacked by more males. Bright males were attacked more by the dominants and dull males by the subordinates. The results show that plumage brightness may affect individual recognition, but also that it is used by males to assess the quality of competitors. Male–male interactions, therefore, may have played a role in the evolution of plumage brightness, either in the context of competition for mates or for resources when males gather into unisexual groups.

The pathogen transmission avoidance theory of sexual selection

The current theory that sexual selection results from female preference for males with good genes suffers from several problems. An alternative explanation, the pathogen transmission avoidance hypothesis, argues that the primary function of showy traits is to provide a reliable signal of current disease status, so that sick individuals can be avoided during mating. This study shows that a significant risk of pathogen transmission occurs during mating and that showy traits are reliable indicators of current disease status. A simulation model of population dynamics linked with pathogen transmission indicates that female choosiness traits are selectively advantageous and spread through the population but because the selective benefit of choosiness depends on the percentage of choosy females and bright males, as sexual selection proceeds the selection pressure is reduced and the process becomes self-limiting rather than runaway. Thus, an epidemic model approach leads to very different conclusions than a constant selection-coefficient population genetic approach. The origin of female choosiness is argued to lie in a general tendency to avoid sick individuals, even in the absence of showy traits, which originate as exaggerations of normal traits that are indicative of good health (bright feathers, vigorous movement, large size). Thus, in this new model the origins of both showy traits and female choosiness are not problematic and there is no threshold effect. This model predicts that when the possession of male showy traits does not help to reduce disease in the female, showy traits are unlikely to occur. This case corresponds to thorough exposure of every animal to all group pathogens, on average, in large groups. Such species are shown with a large data set on birds to be less likely to exhibit showy traits. The good-genes model does not make this prediction. The pathogen transmission avoidance model can also lead to the evolution of showy traits even when selection is not effective against a given pathogen (e.g. when there is no heritable variation for resistance), but can result in selection for resistance if such genes are present. Monogamy is argued to reduce selection pressures for showy traits; data show monogamous species to be both less parasitized and less showy. Overall, the pathogen transmission avoidance hypothesis provides a complete alternative to the good-genes theory and makes new predictions.

Population differences in the roles of size and coloration in intra-and intersexual selection in the collared lizard, Crotaphytus collaris: influence of habitat and social organization

Previous studies have shown that in three Oklahoma population* of collared lizards, Wichita Mountains (WM), Glass Mountains (GM), and Arcadia Lake (AL), sexual dimorphism in body size varies as WM>AL>GM, whereas dorsal color dimorphism varies as GM>WM>AL. Social organization at these sites also differs such that the environmental potential for sexual selection varies as AL>WM>GM. We conducted female choice and male competition laboratory trials to assess whether advantages to large or bright males correlate best with the interpopulation pattern of sexual dimorphism or with that of the environmental potential for sexual selection. Between-population trials involved bright-colored WM males and dull-colored AL males that were matched for size. AL females preferred bright WM males, but WM females did not. WM males had higher agonistic scores in intrasexual contests when aggression was low, but AL males consistently had higher scores when aggression escalated. Within-population trials involved males that were disparate in color but size matched and disparate in size but color matched. Size was important in male contests in all populations. Color brightness was a factor in male trials only at AL. Also, only AL females preferred brighter males, and larger males were not preferred in any population. The importance of intraand intersexual selection in these populations cannot be inferred from the observed pattern of size and color dimorphism. Rather, interpopulation differences in the environmental potential for females to assess and choose from among multiple males, and for males to interact, are most consistent with the observed outcomes. Kty words: collared lizards, Cwtaphytui coUaris, female choice, male aggression, sexual dimorphism, sexual selection. [Bthav Ecol 8:506-517 (1997)]

Plumage Coloration and Conspicuousness in Birds: Experiments with the Pied Flycatcher

-Hypotheses concerning predation, sexual selection, and communication in birds often assume that individuals differ in conspicuousness. However, few studies have tested this by measuring the response of individuals that receive the signals. We investigated the effect of plumage coloration on conspicuousness by presenting caged Pied Flycatchers (Ficedula hypoleuca) to unmated territorial males and measuring the time until a response (either courtship or aggression) from the territorial male was observed. In the first experiment, we presented caged males and females at various distances and degrees of habitat openness. Caged birds elicited responses more rapidly in open than in closed habitats, and response time increased with distance. Black-and-white-colored males seemed to trigger a response more rapidly than brown-colored females, at least in open habitats. In the second experiment, we presented bright-colored males, dull males, and bright-painted dull males. All trials were made at the same distance. Caged birds again elicited more rapid responses in open than in closed habitats. Bright-colored males seemed to trigger a response more quickly than dullcolored males, but only in closed habitats. Painted birds elicited response times intermediate to those of bright and dull males. The difference in interaction between color and habitat in the two experiments is difficult to explain but may have been caused by differences in background related to seasonal development of vegetation. One possible problem with experiments on conspicuousness is that the response may be delayed after the receiver has detected the signal. Field observations of the behavior of territorial birds suggested that this probably did not confound the results of our study. Thus, the results support the intuitive but previously untested hypothesis that a bright and contrasting coloration makes birds more conspicuous to conspecifics. Received 30 December 1995, accepted 10 April 1996. GREAT VARIATION exists in animal coloration both among and within species. This may have evolved in response to predation (Cott 1940; Baker and Parker 1979; Harvey and Paxton 1981; Guilford 1990; Endler 1991; Dumbacher et al. 1992; Gotmark 1992, 1993, 1995), sexual selection (Hamilton and Zuk 1982, Parker 1983, Hill 1991, Sxtre et al. 1994; review in Andersson 1994), intraspecific communication (Rohwer 1975,1982; Whitfield 1986; Slagsvold and Lifjeld 1988; Butcher and Rohwer 1989), or for species recognition (Rowland 1979, Endler 1983, Andersson 1994). Several of these hypotheses assume that an individual with bright or contrasting coloration is conspicuous (i.e. more easily discovered) than one with a dull and cryptic coloration (Cott 1940, Parker 1983, Slagsvold and Lifjeld 1988, Butcher and Rohwer 1989, Endler 1991). 1 Present address: Agricultural University of Norway, Department of Biology and Nature Conservation, P. 0. Box 5014, N-1432 As, Norway. E-mail: svein.dale@ibnf.nlh.no Testing whether various plumage colors and patterns differ in conspicuousness is a difficult task. Birds of different color may differ in detectability to humans (Gotmark and Unger 1994, Gotmark and Hohlfalt 1995), but bird vision is different from and perhaps better than that of humans (Goldsmith 1990). Ideally, response by receivers of the signal (e.g. color), such as a conspecific or a predator, should be measured (Bennett et al. 1994). Experiments also must be designed to ensure that a response can be observed once the subject has received the signal. Pied Flycatchers (Ficedula hypoleuca) vary in plumage color. Males range from black-andwhite (i.e. bright) to brown (i.e. dull), whereas all females are brown (Drost 1936). Males benefit from a bright plumage because they are preferred by females as mates (STtre et al. 1994), but bright males seem to pay a cost in terms of a higher predation risk (Slagsvold et al. 1995; but see Gotmark 1992, 1993, 1995). The benefit of bright plumage may increase if bright individuals are more easily discovered by intruding males and prospecting females (Slagsvold and Lifjeld 1988). However, the cost

Parasite-mediated sexual selection: just how choosy are parasitized females?

Models of parasite-mediated sexual selection have thus far overlooked the potential effects of parasites of females on their hosts’ ability to choose mates. A set of models addressing this issue is developed, each building on the previous one to add complexity and realism to the framework. The selection coefficient for parasite immunity and brightness is estimated using the ratio of the fitness of susceptible males to the fitness of immune males. Parasite-induced reduction in female choosiness can substantially relax the selection for bright, immune males, especially when: (1) immunity to parasites is rare in the population, (2) parasites are not highly aggregated within the host population, (3) parasites are abundant, and (4) the effects of parasites on male brightness or female choosiness are severe. Parasite-induced variability in male brightness is most likely to occur in populations in which parasites are abundant and not aggregated; if females in those populations show a reduced preference for bright males, sexual selection for brightness (and parasite immunity) will still operate but exert a weaker selective pressure.

Mating patterns and a test for female mate choice in Etheostoma spectabile (Pisces, Percidae)

Neither size nor breeding color correlated with spawning success of male orangethroat darters, Etheostoma spectabile (Pisces, Percidae), under natural field conditions. When females were presented experimentally with a simultaneous choice they spent no more time in proximity to large than small males, and were subsequently no more likely to spawn with large than with small males. Females also displayed no preference for bright versus dull males. Males and females did not differ significantly in size. Etheostoma spectabile may lack sexual size dimorphism as a result of the lack of female choice for size and the ineffectiveness of male attempts to monopolize females, or selection may be for increased size of females. Males are not dwarfs because of sperm competition. Contest competition among males appeared to be important in initiating spawnings but many males obtained spawnings by participating in ongoing spawning events. Etheostoma spectabile is an example of a sexually dimorphic species with no evident female preference for male size or color.

BLOOD PARASITES IN BRIGHT BIRDS: TESTING THE HAMILTON-ZUK HYPOTHESIS IN SUB-SAHARAN AFRICA WITH AN IMPROVED STATISTICAL METHOD

Summary Underhill, L.G. & Kalejta-Summers, B. 1995. Blood parasites in bright birds: testing the Hamilton-Zuk hypothesis in sub-Saharan Africa with an improved statistical method. Ostrich 66:10-14. The data contained in a catalogue of avian haematozoa for sub-Saharan Africa were examined in the light of the Hamilton-Zuk hypothesis. The males of 464 passerine species were assigned six brightness scores. The generalized linear model with a binomial distribution and logistic link function is shown to be the appropriate statistical tool for analysing blood parasite data. With caveats, results from the model supported the prediction that bright males tend to be parasitized more frequently. However, the group of species with the highest brightness score, had infection rates similar to the dullest group. When phylogenetic associations were taken into account, support for the Hamilton-Zuk hypothesis was equivocal. Further research on the ecology and natural history of the interactions between blood parasites, their vectors and the birds they infest is needed to decide whether the differences between the lowest and highest infestation rates (23% for the dullest species and 37% for the penultimate brightness score) are biologically meaningful.

Extraordinary Sex Roles in the Eurasian Dotterel: Female Mating Arenas, Female-Female Competition, and Female Mate Choice

The mating system of the Eurasian dotterel, Charadrius morinellus, is compared with what would be expected in sex-role-reversed lekking (i.e., female-female competition and mate choice by males). Female dotterel are potentially polyandrous and, in this study, compete for access to males on mating arenas. Males provide all parental care. Intrasexual plumage variation is prominent in both sexes. Bright females win more of their fights than do dull females because bright females are more likely to initiate fights, and all females are unlikely to attack females brighter than themselves. Also, compared with dull females, bright females do more courting, pair earlier in the season, and are more likely to pair with a bright male. Since bright males are apparently in better physical condition than dull males, we suggest that females prefer males that will be good parents. Thus, as no evidence was found of any active mate choice by males, it seems that females are the more active sex in mate choice. Hence, although competition among females on the mating arenas of the dotterel resembles competition among males on leks, the direction of mate choice does not appear to match the analogy of sex-role-reversed lekking. This observation suggests that competition and mate choice are not simply opposite sex roles-individuals of one sex can both compete for mates and exert mate choice.

Are Conspicuous Birds Unprofitable Prey? Field Experiments with Hawks and Stuffed Prey Species

-The unprofitable-prey hypothesis predicts that birds of prey, when given a choice, should more often attack a cryptic than a conspicuous bird if conspicuousness is a signal of unprofitability. We tested this prediction by exposing pairs of stuffed birds to migrating birds of prey. In experiment 1, we paired the conspicuous White Wagtail (Motacilla alba) with the cryptic Meadow Pipit (Anthus pratensis). In experiment 2, we paired the conspicuous female Great Spotted Woodpecker (Dendrocopos major) with the cryptic female Blackbird (Turdus merula). Automatic cameras documented attacks by birds of prey, mostly accipiters, on the mounts. The numbers of attacks on wagtails and pipits were similar, whereas Blackbirds were attacked much more often than woodpeckers. Experiment 2 thus supports the prediction of the unprofitable-prey hypothesis. Using photographs of the experimental situation, we examined detectability of mounts by human observers. Wagtails and pipits were equally easy to detect from a distance, but woodpeckers usually were easier to detect than Blackbirds. Thus, wagtails and pipits did not differ in long-distance conspicuousness, which may explain the result of experiment 1. To analyze reasons for unprofitability, we presented flesh from woodpeckers and Blackbirds to captive falcons, but found no evidence that woodpeckers are distasteful. Other explanations for why woodpeckers were rarely attacked are discussed. Received 26 April 1993, accepted 17 August 1993. THE PLUMAGE of diurnal birds exhibits striking variation in color patterns, from dull, cryptic patterns in some species to bright red, yellow, or black-and-white in others. The evolution of conspicuous colors in birds has been debated since Darwin (1871) proposed his theory of sexual selection to explain the bright colors of many male birds. Darwin's idea of selection through female choice of bright males was discussed by Hingston (1933), who argued that contest competition among males primarily selected for conspicuous colors (review in Butcher and Rohwer 1989). Several studies have supported both the idea of female choice (e.g. Hoglund et al. 1990, Norris 1990, Hill 1991) and male-male competion (Roskaft and Rohwer 1987, Rohwer and Roskaft 1989). Avian coloration is also related to risk of predation. Cryptic plumages in birds such as nightjars and female ducks suggest an important role for predation. Conspicuous plumages may be antipredator adaptations as well. Certain brightly colored birds are distasteful to hornets, cats, and people and, therefore, may be aposematic (Cott 1947, Cott and Benson 1970, Gotmark 1994a). Recently, two or three apparently

Female kestrels gain reproductive success by choosing brightly ornamented males

Abstract. Female choice with respect to male coloration, and its consequences for fitness, were studied in the European kestrel, Falco tinnunculus. In an aviary experiment, females preferred to approach bright males. Under natural conditions, bright males spent more of their time hunting than dull males. Females mated with bright males produced more offspring than those mated with dull males. The evolution of female preferences for ornamented males has frequently been explained in terms of indirect selection through good genes or a runaway process. It is postulated that, in the kestrel, females can increase their fitness through a 'good parent' process, and that this is sufficient to explain the evolution of female preference.

Parasite distribution and virulence: implications for parasite-mediated sexual selection

The Hamilton-Zuk hypothesis states that females choosing males with more developed secondary sexual traits, i.e. “brighter” males, achieve greater fitness if variability in brightness reflects heritable variation in resistance to parasites. However, several factors will affect the likelihood that parasites play a role in sexual selection in given species. Here, using simple models, we show that because of parasite aggregation on a few hosts, only few breeding males would suffer from reductions in brightness due to parasites. Only in cases where parasites are abundant and show low levels of aggregation among their hosts would there be sufficient variability in brightness among breeding males for female choice of bright, resistant males to evolve. In addition, sufficient parasite-induced variability in brightness among breeding males will only occur in host-parasite systems where pathology is linearly related to the number of parasites per host. The presence of males that are uninfected and bright but genetically susceptible to parasites will also influence the fitness advantages obtained by females choosing bright males. If genetic immunity against parasites is rare in the host population, females can probably only benefit from choosing bright males if parasites are common and little aggregated among males. These results greatly limit the generality of the Hamilton-Zuk hypothesis, and suggest that only a small fraction of host-parasite associations could promote the evolution of host mate choice for resistance based on brightness.

Conspicuous coloration in male birds is favoured by predation in some species and disfavoured in others

Conspicuous plumage in male birds may evolve through competition between males and choice of bright males by females. Male brightness might be constrained by increased risk of predation or other mortality agents. Alternatively, bright male birds may signal to predators that they are unprofitable as prey. These hypotheses, which have been difficult to test, were examined in a field experiment where stuffed chaffinches Fringilla coelebs and pied flycatchers Ficedula hypoleuca were exposed to sparrowhawks Accipiter nisus on spring migration in Denmark. The hawks attacked the colourful male chaffinches more often than the cryptic female chaffinches. In the flycatcher, however, hawks attacked the cryptic females more often than the conspicuous males. Risk of predation is therefore likely to influence the evolution of male coloration. It may, however, select against conspicuous plumage in some species, but favour it in others.

Costs influences sequential mate choice in sticklebacks, Gasterosteus aculeatus

In nature females can usually choose among males only sequentially. Recent models of sequential choice predict that, with increasing costs of sampling, selectivity for preferred males should decline. In our tests female sticklebacks were highly selective in their sequential choice between dull and bright males when costs were low. With increasing time and energy costs of moving between males, they reduced their selectivity. In particular, when the females had to swim against a current, dull males when met became highly acceptable. The females’ response to increased costs of sampling shows that they make the kind of economic decisions predicted by models of sequential choice. The strength of sexual selection by female choice therefore depends on the spatial structure of the population.

Anti-predator effect of conspicuous plumage in a male bird

Sexual selection theory suggests that conspicuous plumage in male birds evolves through contest competition between males and choice of bright males by females. A basic assumption is that brightness is limited by increased predation or other mortality agents. Alternatively, the unprofitable prey hypothesis suggests that conspicuous birds signal to predators that they are difficult to catch. In this study, stuffed pied flycatchers, Ficedula hypoleuca, were exposed to sparrowhawks, Accipiter nisus. Contrary to the assumption of sexual selection theory, the hawks attacked dull-coloured females more often than conspicuous males. These results provide the first experimental evidence for the unprofitable prey hypothesis, and suggest that predation may sometimes reinforce sexual selection processes.