Is Mate Provisioning Predicted by Ornamentation? A Test with Northern Cardinals (Cardinalis cardinalis)

Male birds of many species feed their mates during courtship and incubation. The amount of food provided can be substantial and even essential for successful reproduction in some species, and can influence female nest attentiveness in many others. Additionally, mate provisioning may predict later nestling feeding rates. Females may thus benefit from being able to determine male provisioning effort. We assessed the expression of several ornaments, known to indicate condition in male northern cardinals (Cardinalis cardinalis), and compared these with mate provisioning rates, nestling feeding rates, and nest attentiveness. We found that male ornamentation may not be indicative of mate provisioning rates. Mate provisioning rate did not co‐vary with reproductive success, male feedings to nestlings, or nest attentiveness of females. However, females which were fed more often during incubation tended to provision nestlings less. Reduced female parental effort following extensive incubation feeding may be indicative of females using incubation feeding to assess future male parental effort. Male hormonal condition that favors high rates of nestling provisioning may be a proximate cause of mate provisioning during incubation, even in the absence of selection, favoring high rates of mate provisioning. Both sexes may have capitalized on this unselected behavior.     

Sexual pigmentation and parental risk‐taking in yellow warblers Setophaga petechia

Adult‐directed predation risk imposes important behavioral constraints on parents and might thus alter relationships between costly sexual ornaments and parental performance. For instance, under low predation risk, highly ornamented individuals might display better parental performance than others, as predicted by ‘good parent’ models of sexual selection. However, under high risk of predation, highly ornamented individuals might abandon parental effort if conspicuous to predators, or if social partners are more willing to take parental risks when paired with highly ornamented mates. We experimentally elevated perceived adult‐directed predation risk near nests to explore how carotenoid‐ and phaeomelanin‐based pigmentation in both sexes relate to parental risk‐taking for offspring in the yellow warbler Setophaga petechia. Compared to other males, males with more intense carotenoid‐based pigmentation maintained higher levels of paternal effort under predation risk at highly concealed nests, but reduced nestling provisioning rate more at exposed nests. Further, when faced with predation risk, females with more phaeomelanin‐based pigmentation reduced nestling provisioning rate less than other females, regardless of nest concealment. Females displayed higher parental effort across treatments when paired to males with more colorful carotenoid pigmentation. However, birds did not reduce parental effort under risk less when paired to a highly ornamented mate, suggesting that predation risk did not accentuate differential allocation. Males did not take fewer parental risks than females. Results indicate that nest concealment modifies parental risk‐taking by males with colorful carotenoid‐based pigmentation, and suggest that female melanin‐based pigmentation may indicate boldness and greater a propensity to take parental risks.     

Female ornaments in the Pied Flycatcher Ficedula hypoleuca: associations with age, health and reproductive success

Female ornamentation has received little attention in studies of sexual selection. Traditionally, female ornaments have been explained as a genetically correlated response to selection in males. However, recent findings suggest that female ornaments may be adaptive. Southern populations of Pied Flycatchers Ficedula hypoleuca are suited for studies of female ornamentation because, in addition to the white wing patch, some females also express the white forehead patch characteristic of males. We thus addressed the associations of these two ornaments with female age and with some health and breeding parameters in a Spanish population of Pied Flycatchers. Female ornament expression was not associated with haemoparasite prevalences, clutch size or parental provisioning effort. However, females expressing the white forehead patch raised more fledglings, and females with larger wing patches bred earlier, had higher number of hatchlings and showed increased levels of total serum immunoglobulins. Thus, these two unrelated epigamic ornaments may indicate some aspects of female quality. Further experimental studies could test the possibility that these plumage traits might function as signals to the males or might be used during female–female aggressive encounters in competition for nest-sites and mates.     

High brood patch temperature of less colourful,less pheomelanic female Barn Swallows Hirundo rustica

In birds, even a minor difference in egg temperature (1–1.5 °C) has been shown to affect the fitness of offspring by changing hatching success, incubation period and nestling quality. Female, but not male, passerines develop brood patches. Thus if there are traits, such as plumage ornamentation, that indicate optimal egg temperature, males should pair with females that exhibit those traits. However, no study has yet investigated the relationship between female brood patch temperature, which would directly affect egg temperature, and female plumage ornamentation. In this study, we examined the surface temperature of female brood patches during nocturnal incubation and examined its relationship with female plumage ornaments in Asian Barn Swallows Hirundo rustica gutturalis. After controlling for ambient air temperature, brood patch temperature was negatively associated with colour saturation of the female throat patch. No other female ornaments, such as tail‐length, white tail spots or throat patch size, predicted brood patch temperature. When oral (mouth) temperature was statistically controlled, females with less colourful throats and longer tails showed higher brood patch temperature, indicating that these females had hotter brood patches in relation to the temperature of other body parts. Furthermore, we found a negative relationship between pheomelanin pigmentation and brood patch temperature after controlling for ambient air temperature or oral temperature. To our knowledge, this is the first study to show that female ornaments can predict the absolute/relative thermal investment in brood patches. This relationship, together with other aspects of female quality, may affect male mate preference and female ornamentation.     

More colourful eggs induce a higher relative paternal investment in the pied flycatcher Ficedula hypoleuca: a cross-fostering experiment

The signalling hypothesis of eggshell colouration in birds posits that females of species with blue-green eggs signal their phenotypic quality or the quality of their eggs to their mates through deposition of the antioxidant biliverdin as pigment. Males respond by investing more in the offspring. Through a cross-fostering experiment where we have exchanged whole clutches between pairs of pied flycatcher Ficedula hypoleuca nests, we managed to break potential associations between female quality and clutch chromaticity. We show that males respond to incubated clutches with more variable and higher peak values in blue-green chroma through a higher proportional investment in nestling provisioning on day 4 of the nestling period, when males invest more heavily than females in provisioning. More variable clutches show higher peak chroma values. We also show that egg colour during the two-week incubation period has a significant effect, which is not found for the colour of eggs during the laying period. Finally, the proportion of male provisioning visits affects negatively female brooding effort and nestling mortality, and thereby has positive effects on female fitness. Blue-green chroma in the pied flycatcher functions as a signal of female or clutch quality to males which respond by adjusting their relative investment with respect to total pair effort.     

Paternal care as a conditional strategy: distinct reproductive tactics associated with elaboration of plumage ornamentation in the house finch

When individuals in a population differ in physiological conditionand residual reproductive value, selection should favor phenotypicplasticity in reproductive investment such that individualsare able to adopt the reproductive tactic that results in thehighest fitness under given conditions. Here we examined reproductivetactics in relation to the elaboration of condition-dependentsexual ornamentation (carotenoid breast coloration) in a Montanapopulation of the house finches (Carpodacus mexicanus). Malesused distinct reproductive tactics depending on elaborationof their sexual ornamentation. Males with red pigmentation (maximum ornament elaboration) paired with females that nestedearlier, but these males did little provisioning of incubatingfemales and nestlings. In contrast, males with yellow colorationpaired with females that nested later, but these males fedfemale and nestlings more. Consequently, for red males offspringrecruitment was primarily affected by earlier nest initiation, whereas in yellow males it was affected most by male provisioning.In males with intermediate plumage coloration, all measuredcomponents, nest initiation, provisioning of incubating female,and nestling feeding, strongly contributed to offspring recruitment.The fitness consequences of alternative reproductive tacticsof males were influenced by breeding experience and fidelityof their mates. Among first-time breeders, red males achievedthe highest fecundity because of the advantage gained throughearly nesting and pairing with more experienced females andbecause of compensation by their mates for low male provisioningof nestlings. Among experienced breeders, males with intermediateplumage coloration achieved the highest fecundity because ofthe combined benefits of relatively early pairing and high parental care. High variation in sexual ornamentation in a Montana populationof house finches may favor distinct associations of sexualdisplays with a particular set of reproductive behaviors.     

Mate choice in Darwin's Finches

Female Geospiza conirostris on Isla Genovesa, Galapagos, pair preferentially with males who have had previous breeding experience. They choose mates on the basis of courtship behaviour and black adult plumage. By mating with experienced black males, they gain a fitness advantage in terms of fledgling production and recruitment of young into the breeding population. Behavioural signs of past breeding experience and black plumage are reliable age- and condition-dependent traits. We suggest that females use conspicuous black plumage to identify old males at a distance, then interactions through courtship to modify initial assessments. Females paired with inferior males may increase the genetic quality of their offspring by extra-pair copulations; results of heritability analysis of morphology are consistent with this suggestion. Females change mates at a frequency of 12–27% per breeding season. They re-pair with males who are generally old, experienced, and hold territories adjacent to the deserted male. Females that re-pair gain a benefit, whereas males who are deserted within a breeding season incur a cost of more than 50% of their future potential production for that season. We conclude that females in choosing males seek reliable indicators of potential parental care, and in addition they may seek indicators of genetic quality.     

Female collared flycatchers choose neighbouring and older extra‐pair partners from the pool of males around their nests

Extra‐pair copulation is common among passerine birds. Females might engage in this behavior to obtain direct or indirect benefits. They may choose extra‐pair males with larger ornaments, especially if they are costly to produce. Here we studied extra‐pair paternity in the collared flycatcher. Genetic analysis allowed us to identify the presence or absence of extra‐pair young in the focal nests, and to identify extra‐pair fathers. We also identified potential males available as extra‐pair sires around the nests of females who had extra‐pair young. First, we tested the relationship between paternity in own nest and ornament size (wing patch and/or forehead patch), morphological traits and age of social males and females. Second, we compared the same suite of traits among social mates, extra‐pair males and all potential extra‐pair mates. Finally, we investigated the effect of the size of ornaments on the distance between the social nest and that of nest the extra‐pair father. Contrary to our prediction, males with larger ornaments and longer wings lost more paternity in their nests. We also found that early breeders lost less paternity in their nests. Extra‐pair males were older and had longer wings than social and potential extra‐pair males. Females mainly obtained extra‐pair mates near their nests but the distance did not vary according to ornamentation. These results could potentially be explained by differences in mate guarding strategy as older males may be more experienced in guarding their mate and attract other females more easily. More data about mate guarding and prospecting are needed to increase our understanding of mechanisms underlying the extra‐pair paternity in birds.     

Handicapped females receive more feedings during incubation from their mates: support for the female nutrition hypothesis

The female nutrition hypothesis posits that provisioning intensity of incubating females by their mates may depend on female needs and ensure proper incubation and a corresponding high hatching and breeding success of breeding pairs. Here, we have handicapped female pied flycatchers Ficedula hypoleuca at the beginning of incubation by clipping two primaries on each wing and filmed nests during incubation and later nestling provisioning to estimate male involvement in incubation feeding at the nest and in offspring care. Incubation feeding was more frequent at late nests. Correcting for this seasonal effect, incubation feeding was significantly affected by treatment and twice as high at experimental as at control nests. There was no effect of the experiment on female incubation attendance. The handicap did not result in any effect on hatching and breeding success, nestling growth and male or female provisioning and mass at the end of the nestling period. Males adjust their incubation feeding activity at the nest to female energetic requirements during incubation.     

Females Paired with New and Heavy Mates Reduce Intra-Clutch Differences in Resource Allocation

Reproductive investment affects both offspring and parental fitness and influences the evolution of life histories. Females may vary their overall primary reproductive effort in relation to the phenotypic characteristics of their mate. However, the effects of male quality on differential resource allocation within clutches have been largely neglected despite the potential implications for mate choice and population dynamics, especially in species exhibiting biparental care and brood reduction. Female southern rockhopper penguins Eudyptes chrysocome paired with heavy mates reduced intra-clutch variation in egg and albumen masses. Females paired with new mates also reduced intra-clutch variation in yolk androgen levels. Since both an increased mass and increased androgen concentrations positively influence chick survival under sibling competition, the chances of fledging the whole clutch are likely to be higher for newly formed pairs with heavy males than for previously formed pairs with light males. Interestingly, total clutch provisioning did not vary with male quality. We show for the first time that females vary intra-clutch variation in resource allocation according to male quality. In species with brood reduction, it may be more adaptive for females to modulate the distribution of resources within the clutch according to breeding conditions, than to change their total clutch provisioning.     

Experimental evidence that brighter males sire more extra‐pair young in tree swallows

Across taxa, extra‐pair mating is widespread among socially monogamous species, but few studies have identified male ornamental traits associated with extra‐pair mating success, and even fewer studies have experimentally manipulated male traits to determine whether they are related directly to paternity. As a consequence, there is little experimental evidence to support the widespread hypothesis that females choose more ornamented males as extra‐pair mates. Here, we conducted an experimental study of the relationship between male plumage colour and fertilization success in tree swallows (Tachycineta bicolor), which have one of the highest levels of extra‐pair mating in birds. In this study, we experimentally dulled the bright blue plumage on the back of males (with nontoxic ink markers) early in the breeding season prior to most mating. Compared with control males, dulled males sired fewer extra‐pair young, and, as a result, fewer young overall. Among untreated males, brighter blue males also sired more extra‐pair young, and in paired comparisons, extra‐pair sires had brighter blue plumage than the within‐pair male they cuckolded. These results, together with previous work on tree swallows, suggest that extra‐pair mating behaviour is driven by benefits to both males and females.     

Parental Feeding Rates in the House Sparrow,Passer domesticus: Are Larger‐Badged Males Better Fathers?

Elaborated secondary sexual characteristics may reflect genetic quality or good health, either of which may be associated with an individual's competence as a parent. We examined whether female house sparrows (Passer domesticus) paired to large vs. small‐badged mates gain benefits in the form of increased parental care or improved nestling welfare. House sparrow nests where the male had been trapped and banded were observed for 1 h on at least 5 d during the peak growth period of nestlings. Male feeding shares, measured as the proportion of total feeds per chick made by the male, were marginally positively correlated with male badge size. Moreover, higher male shares of nestling feeding were associated with improved prospects for offspring survival, and a greater proportion of chicks fledged from the nests of larger‐badged males. These results suggest that females paired to large‐badged males gain direct benefits in the form of enhanced nestling survival, which presumably stem from factors associated with increases in the proportion of nestling feeding contributed by their mates.     

Predation by sparrowhawks Accipiter nisus on male and female pied flycatchers Ficedula hypoleuca in relation to their breeding behaviour and foraging

Bright plumage, song display, and aggressive resource defence in males may cause higher predation on males than on females during the breeding season. However, in birds, higher predation on females is sometimes observed. Parental investment may be high in females (egg-laying, incubation and feeding of offspring), which might lead to a high risk of predation. We studied predation by sparrowhawks Accipiter nisus in relation to behaviour in pied flycatchers Ficedula hypoleuca where breeding males are more conspicuous than females in plumage and behaviour. Male pied flycatchers generally occupied more exposed perches than females. Females were more mobile and foraged more than males, especially prior to and during incubation. During the incubation and nestling stages, when predation on the sexes could be directly compared, sparrowhawks took about the same number of male and female pied flycatchers. During incubation, however, females spent about 77% of the day in the nest and were 4.7 times more vulnerable than males per unit of time available (i.e. outside the nest). A comparison with the chaffinch Fringilla coelebs , where hawks took more females than males, indicates that timing of breeding, foraging behaviour and parental roles of males and females affect predation risk.     

Phenotypic plasticity in breeding plumage signals in both sexes of a migratory bird: responses to breeding conditions

Adaptive phenotypic plasticity may respond to present ambient conditions. Sexual and social signals in both sexes may express phenotype performance. Plumage signals that change discontinuously allow relating discrete variation to previous performance. Both sexes of the pied flycatcher Ficedula hypoleuca present white patches on the wings and on the forehead, which constitute sexual and social signals. Forehead patches are moulted together with body plumage in Africa, while wing patches are partly moulted in Africa and partly in the breeding area soon after breeding. We studied individual inter‐year changes (corrected for regression to the mean) in the size of forehead and wing patches of both sexes in seven years for females or six years for males in two nearby study areas in central Spain. We found that initial signal extent strongly delimits the possible subsequent changes negatively. There is a negative association of male age with forehead patch changes. Cold and rainy springs are associated in females with decreases in both patch areas and vice versa, while no association with climate is observed in male wing patch changes. Cold pre‐breeding conditions predict positive changes in female wing and male forehead patches. Breeding success is positively associated with forehead patch changes in females. Late‐breeding males experience more positive changes in forehead patch size than early‐breeding males. Some of these trends can be explained by variable costs of breeding in certain conditions for subsequent signal production and/or maintenance, while absence of trends in some cases may be explained by sex differences in costs of breeding and interactions with phenotypic quality of breeders.     

Paternal care and male mate-attraction effort in the European starling is adjusted to clutch size

In facultative polygynous birds with biparental care, a trade-off may occur between male parental care and attraction of additional mates. If there is a cost associated with reduced male parental care, the relative benefit of mate attraction may be predicted to decrease as the size of a male's clutch or brood increases. We tested this prediction in monogamous pairs of facultatively polygynous European starlings (Sturnus vulgaris). The larger the clutch, the more time the male spent incubating and the less time he spent attracting an additional female (i.e. singing near and carrying green nesting material into adjacent empty nest-boxes). Reduced paternal incubation resulted in lower overall incubation (the female did not compensate) and lower hatching success. Immediately after experimental reduction of clutches, males spent significantly less time incubating and more time singing and carrying greenery, and vice versa for experimentally enlarged clutches. Males with experimentally reduced clutches attracted a second female more often than males with experimentally enlarged clutches. This is the first study, to our knowledge, to provide experimental evidence for an adjustment of paternal care and male mate-attraction effort to clutch size. However, a trade-off between paternal nestling provisioning and mate attraction was not revealed, probably due to the absence of unpaired females by that time in the breeding season. Experiments showed that the relative contribution of the male and female to nestling provisioning was unrelated to brood size.     

Postcopulatory female choice increases the fertilization success of novel males in the field cricket, Gryllus vocalis

Although recent studies have demonstrated that female crickets prefer novel males to previous mates, the relative contribution of pre- and postcopulatory behaviors to this advantage remain unknown, as do the reproductive consequences to males. I paired females either with previous or novel mates, and recorded the latency to mating and the time after mating at which the female removed the male's spermatophore, terminating sperm transfer. Females that mated with familiar males removed their spermatophores sooner than females that mated with novel males. Females paired with novel males also mated more quickly than females paired with familiar males, but this difference was not statistically significant. A molecular-based paternity analysis was used to determine whether the postcopulatory preference of females for novel males influences a male's fertilization success. Females were assigned to either mate three times with the same male and then once with a novel male, or four times with four different males. The paternity of the last male was higher when the female previously had mated repeatedly with the same male than when she had mated previously with different males. These results suggest that female spermatophore removal behavior influences male paternity such that novel males receive a fertility benefit.     

Dynamics of House Sparrow Biparental Care: What Contexts Trigger Partial Compensation?

Nest attendance during incubation is characterized by an inequitable division of labor in house sparrows, Passer domesticus, with females spending more time at the nest than males. Previous research has shown that if male contributions are reduced experimentally via testosterone (T) implants, females compensate partially for those reductions, consistent with predictions from most models of negotiated biparental care. In this study, we attempted to identify the cues and contexts generating partial compensation, using data from both unmanipulated parents and pairs with T‐males. Both males and females of this species sometimes leave the nest before their mate returns to relieve them, and we found that these unrelieved departures by unmanipulated individuals occur when partners are on lengthy recesses. Females compensated partially for long male recesses by marginally extending their bouts; most females also slightly reduced their next recess. By contrast, when males left before their mate returned, they left earlier than when they waited for the female. Neither males nor females adjusted their recess lengths after returning to the nest and discovering that their partner was absent. More pronounced changes in nest attendance of unmanipulated parents occurred in the context of ‘visits’, when individuals returned to the nest but then left without relieving their mate. Such visits effectively prolonged the bout of the on‐duty partner and extended the visitor’s recess. Analyses of behavior of T‐males and their mates revealed that T‐males had significantly longer recesses than control males, and that their mates, in turn, had elevated rates of unrelieved departures. T‐males also visited their on‐duty mates more often than control males, whereas female visits to T‐males were rare. Collectively, the predicted changes in female nest attendance associated with lengthy male recesses and male and female visits account reasonably well for the compensatory response of females paired to T‐males. The majority of female compensation was attributable to changes in visit behavior, however, suggesting that much of the negotiation over nest attendance in this species occurs during direct interactions between mates.     

Reproductive correlates of plumage coloration of female Mountain Bluebirds

Many studies have shown that the plumage coloration of male birds can act as an honest signal of quality, indicating benefits that a female could gain from pairing with a specific male. In some species, females also display ornamental plumage, but less is known about the function and potential adaptive significance of female coloration because most research has focused on male coloration. Male Mountain Bluebirds (Sialia currucoides) display full body, ultraviolet (UV)‐blue plumage, whereas female plumage is more subdued, with blue color focused on the rump, wing, and tail. During the 2011 and 2012 breeding seasons (May–July) near Kamloops, BC, Canada, we examined coloration of the rump and tail of female Mountain Bluebirds to determine if their plumage could act as an indicator of direct reproductive benefits (e.g., enhanced parental care or reproductive success) to potential mates. We found no relationship between female plumage coloration and either provisioning rate or fledging success. However, female coloration varied with age, with after‐second‐year (ASY) females having brighter, more UV‐blue tail feathers than second‐year (SY) females. In addition, ASY females with brighter, more UV‐blue tails had larger clutches. We also observed positive assortative mating by tarsus length. Because previous work with other species suggests that female body size may be a good predictor of breeding success, males could potentially benefit from pairing with larger females. However, reproductive success did not vary with female size in our study. Although our evidence that structural plumage coloration of female Mountain Bluebirds is a signal of direct reproductive benefits for males (e.g., higher reproductive success) is limited, our results (i.e., ASY females with brighter tails than SY females, and ASY females with brighter tails having larger clutches) do suggest the potential for sexual selection to act on female coloration.     

Mutual ornamentation and the parental behaviour of male and female Collared Flycatchers Ficedula albicollis during incubation

One of the benefits of mate choice based on sexually selected traits is the greater investment of more ornamented individuals in parental care. The choosy individual can also adjust its parental investment to the sexual signals of its partner. Incubation is an important stage of avian reproduction, but the relationship between behaviour during incubation and mutual ornamentation is unclear. Studying a population of Collared Flycatchers Ficedula albicollis, we monitored the behaviour of both sexes during incubation in relation to their own and their partner's plumage traits, including plumage‐level reflectance attributes and white patch sizes. There was a marginally positive relationship between male feeding rate during incubation and female incubation rate. Female but not male behavioural traits were associated with the laying date of the first egg and clutch size. The behaviour of the two sexes jointly determined the relative hatching speed of clutches and the hatching success of eggs. Females with larger white wing patches spent less time incubating eggs and left the nestbox more frequently. Males with larger white wing patches fed females less frequently, whereas males with brighter white plumage areas visited the nestbox more regularly without feeding. Females tended to leave the nest less often when mated to males with larger wing patches, and females spent less time incubating when males had more UV chromatic plumage. The behaviour of both partners during incubation therefore predicted hatching patterns and was correlated with their own and sometimes with their partner's plumage ornamentation. These results call for further studies of mutual ornamentation and reproductive effort during incubation.     

POPULATION DIVERGENCE IN SEXUAL ORNAMENTS: THE WHITE FOREHEAD PATCH OF NORWEGIAN PIED FLYCATCHERS IS SMALL AND UNSEXY

Models of sexual selection suggest that populations may easily diverge in male secondary sexual characters. Studies of a Spanish population of the pied flycatcher, Ficedula hypoleuca, and a Swedish population of the closely related collared flycatcher, F. albicollis, have indicated that the white forehead patch of males is a sexually selected trait. We studied the white forehead patch of male pied flycatchers (n = 487) in a Norwegian population over seven years. Males with large forehead patches were in general more brightly colored, but patch height was not correlated to body mass, body size, or parasite loads. Conditions during the nestling period did not seem to influence patch height as an adult. Patch height increased slightly from the first to the second year as adults, but then remained relatively constant at higher ages. Patch height was not related to survival. Year-to-year changes showed that males who increased in patch height also increased in body mass, suggesting that expression of the forehead patch may be partly condition dependent. However, changes in body mass explained only a small proportion of the variance in patch height between males. Thus, patch height would not be a good indicator of male quality. Furthermore, patch size was also not related to male ability to feed nestlings, indicating that females would not obtain direct benefits by choosing males with large patches. However, patch height could be a Fisher trait, but this requires heritability and there was no significant father-son resemblance in patch height. Comparisons of the males visited by each female during the mate sampling period indicated that chosen males did not have larger forehead patches than rejected males. Experimental manipulation of patch height did not affect male mating success. These results indicate that females do not use patch size as a mate choice cue. Finally, patch height did not predict the outcome of male contests for nestboxes, suggesting that the forehead patch is not an intrasexually selected cue of status. Norwegian pied flycatchers have smaller forehead patches than both Spanish pied flycatchers and Swedish collared flycatchers. We suggest that this pattern may be explained by the lack of sexual selection on the forehead patch in the Norwegian population as compared to the other populations, where the patch is apparently sexually selected. We discuss possible reasons for these population divergences, such as female choice on an alternative secondary sexual character (general plumage color) and speciation among Ficedula flycatchers.