Costs and benefits of variable breeding plumage in the red-backed fairy-wren

The red-backed fairy-wren is a socially monogamous passerine bird which exhibits two distinct types of breeding male, bright males that breed in bright red and black plumage and dull males that breed in dull brown plumage. Most males spend their first potential breeding season in dull plumage and subsequent breeding seasons in bright plumage, but a relatively small proportion of males develop bright plumage in their first breeding season. This study quantifies morphology, behavior, and reproductive success of dull and bright males to assess the adaptive costs and benefits of bright plumage while controlling for age. Older bright males (two years of age or older) attempted to increase their reproductive success via copulations with extrapair females, whereas younger (one-year old) bright males and dull males did not. Thus, older bright males spent less time on their own territories, intruded on neighboring groups with fertile females more frequently, gave more courtship displays, and had larger sperm storage organs than did younger bright males and dull males. Microsatellite analyses of paternity indicate that the red-backed fairy-wren has extremely high levels of sexual promiscuity, and that older bright males had higher within-brood paternity than dull males or younger bright males. Regardless of age, bright males were more attractive to females in controlled mate choice trials than were dull males, and both age classes of bright males obtained higher quality mates earlier in the breeding season than did dull males, when nesting success was higher. In conclusion, although it appears that bright plumage increases access to higher quality mates, age also plays a central role in determining a male's overall reproductive success because of the high levels of sexual promiscuity exhibited by the red-backed fairy-wren.     

EXTRAPAIR MATE CHOICE AND HONEST SIGNALING IN COOPERATIVELY BREEDING SUPERB FAIRY-WRENS

In many species of monogamous birds females copulate with males other than their social mates, resulting in extrapair fertilizations. Little is known about how females choose extrapair mates and whether the traits used to choose them are reliable indicators of male quality. Here we identify a novel male trait associated with extra-group mating success in the superb fairy-wren (Malurus cyaneus), a cooperatively breeding bird with one of the highest known frequencies of extra-group mating. Female fairy-wrens chose extra-group mates that molted earlier into breeding plumage. Males molted up to five months before the breeding season began, and only males that molted at least one month prior to its onset gained any extra-group fertilizations. This conclusion held after controlling statistically for the effect of age and social status on molt date. Once males acquired breeding plumage, they began courtship display to females on other territories. Thus, some males were displaying to females for several months before the breeding season began. This extraordinarily long period of advertisement by males may be facilitated by the long-term ownership of territories. We suggest that early acquisition of breeding plumage or the subsequent display behavior can be reliable cues for mate choice because they are costly to acquire or maintain.     

Parental care in Semipalmated Sandpipers Calidris pusilla: brood desertion by females

Although Semipalmated Sandpipers Calidris pusilla are monogamous, with biparental incubation, most females (86–97%) deserted their broods to the care of their mates, 0–11 days (average 6) after their eggs hatched. Males left the brood an average of 8 days later, shortly before or after the chicks fledged. In several instances, females that deserted in one year remained with the chicks the next year, and vice versa. Females deserted chicks at nests that hatched later in the season at an earlier age than those had hatched earlier ( r ²> o.6). Since females appeared to have an energy deficit in at least some years, and suffered higher mortality rates than males during breeding, it is possible that females deserted broods in order to take advantage of better feeding conditions at migratory stopovers in northeastern North America early in the season. There was little evidence of higher nesting success or earlier hatching date in reuniting pairs, although if both members of a pair returned to the breeding area, 80% reunited. Increased survival of their mate may be most advantageous to males in ensuring that they obtain a female the following year.     

Female Sexual Interference in the Smooth Newt,Triturus vulgaris vulgaris

Competition between unmated females for males was observed in the smooth newt, T. vulgaris, during the early part of the breeding season. Females interfered at the spermatophore-transfer stage of courtship, preventing a rival female from picking up the sperm mass. Interference often resulted in the rival female abandoning the courtship encounter. In many of the encounters (70%), the interfering female was inseminated. However, interference between females was not observed after the commencement of ovulation. By contrast, the incidence of sexual interference between males was low during the preovulatory period and increased significantly post-ovulation. Sexual interference in newts and salamanders has previously only been observed between males. During the greater part of the breeding season, when females are ovipositing, eggs are the limiting resource and males compete for access to receptive females. However, this study suggests that early in the breeding season, prior to commencement of ovulation, the limiting resource may temporarily be sperm, due to the physiological constraint of spermatophore production. This may lead to female competition for mates.     

Timing of prenuptial molt as a sexually selected indicator of male quality in superb fairy-wrens (Malurus cyaneus)

Seasonally dichromatic male superb fairy-wrens (Malurus cyaneus)solicit extra-group fertilizations through displays of theirbrightly colored nuptial plumage during visits to females inneighboring territories. This ornamental plumage is lost atthe end of the breeding season, and reacquired before the nextbreeding season after a highly variable period spent in a cryptic,female-like, "eclipse" plumage. Individuals start visiting femalesas soon as they return to nuptial plumage, often several monthsbefore the start of breeding.We examine variation in the timingof acquisition of nuptial plumage in relation to environmentalconditions and the age, social status, and condition of males.We show that males undergo the prenuptial molt earlier as theyage and when in superior condition, and that molt is delayedin years of more adverse winter weather conditions. We proposethat the purpose of male displays may be to advertise theirquality, and that females use this variation in the timing ofacquisition of nuptial plumage to assess the relative qualityof prospective extra-group mates. Molting earlier is apparentlycostlier, so this handicap would appear to be a reliable reflectionof male quality.     

Sexual Signals of the Male American Goldfinch

Male American goldfinches (Carduelis tristis) exhibit conspicuous yellow plumage, orange bills, and black caps during the breeding season. These secondary sexual characteristics may serve as criteria by which females evaluate males as potential mates because the traits vary among individuals and are likely to be costly. We quantified plumage and bill color and cap characteristics of wild, free‐ranging American goldfinches during the breeding season and tested for relationships between those features, body condition and individual genetic diversity in males. Overall, male and female goldfinches were highly sexually dichromatic, with plumage saturation and brightness and bill brightness contributing strongly to the dimorphism. Body condition decreased significantly with Julian date, even over the 2‐wk period immediately prior to the onset of nesting during which we collected our color and cap measurements. Principal components describing color of the back and the bill significantly predicted date‐corrected body condition based on quadratic regressions, suggesting that there is reliable information in back and bill color that females could use when choosing mates. In a subset of captive males, we found that bill hue faded from orange to yellow within 24 h of capture, suggesting that bill color may reflect short‐term changes in health status or carotenoid availability. Individual genetic diversity based on a panel of eight microsatellite loci was correlated with back brightness and perhaps with cap symmetry. Based on the results of this field study, ornamentation of male American goldfinches appears to signal both long‐ and short‐term aspects of phenotypic quality.     

Non-breeding behaviour of Magenta Petrels Pterodroma magentae at Chatham Island, New Zealand

Magenta Petrels Pterodroma magentae were caught at light-attraction stations on southwest Chatham Island, New Zealand, and most were fitted with transmitters. Of 52 captured since 1993, 71% were males, and all 36 tracked adequately proved to be non-breeders in the breeding season of capture. Our data indicated no sex bias in their probability of being captured at lights. Males provided 86% of trackings, and 87% of trackings of birds flying over the breeding area were males. Males landed 118 times; females 13 times. Only males were found on the ground, by night and day, apparently unassociated with burrows (three with and ten without transmitters), but subsequently digging burrows ( n  = 8). Of 19 birds banded as fledglings up to 2000, males were first recaptured nearing 4 years old (at lights and on the ground) and a female nearing 6 years old (in burrow). Among 37 fledglings, the sex ratio was even. Nine tracked males occupied burrows, as did two females, but the latter were older recaptures (10+ and 25+ years old). It appears that only males claimed existing, or dug new, burrows. They then attracted a mate to the burrow by means unknown, but from among females frequenting an inshore courtship area near the colony, or occasionally flying over the colony, at night. Females established in burrows, but then losing their mate, were able to re-mate there, by calling from near the burrow or by attracting a mate in flight or from the postulated inshore courtship area. Both sexes sometimes took years to pair or re-mate, possibly reflecting the dearth of available mates.     

Plumage redness predicts breeding onset and reproductive success in the House Finch: a validation of Darwin's theory

Darwin (1871) and later Fisher (1958) suggested that sexual selection can drive the evolution of ornamental traits in monogamous species when female preferences for these traits allow well-ornamented males to begin breeding earlier in a season and, as a result, gain reproductive advantages over poorly ornamented males. However, few studies have been conducted to test this fundamental concept upon which much of the sexual selection theory for monogamous species has been based. In this study, we examined the relationship between breeding onset, reproductive success, and male ornamentation in the House Finch Carpodacus mexicanus , a species in which males display bright carotenoid-based plumage pigmentation. In previous work, it has been shown that bright male House Finches are preferred as social mates by females and, as a result, begin nesting earlier in the season than do drab orange and yellow males. Here we show that, by initiating breeding earlier in the season, brightly colored males fledge more offspring in a season than do drab males. Thus, differential timing of breeding generates considerable variance in reproductive success among male House Finches and contributes to sexual selection for male plumage ornamentation in this species.     

Females Paired with More Attractive Males Show Reduced Oxidative Damage: Possible Direct Benefits of Mate Choice in Pied Flycatchers

Direct benefits of female mate choice may concern female fertility and fecundity but also physiological status. In birds with biparental care, males may contribute to improve the condition and health of their pair‐mates through help in constructing nests, incubation or incubation feeding and nestling provisioning. They may also reduce harassment of females by non‐pair males. A consequence of these male activities could be expressed in terms of oxidative damage, which may depend on metabolic effort and social stress. Here, we have related male contribution to parental and territorial duties to female oxidative status in the pied flycatcher Ficedula hypoleuca, a species where preferred males present darker dorsal plumage and, in Iberian populations, a large white forehead patch. Darker males were paired with females with high incubation attendance and reduced nestling provisioning rates, which may lead to reduced female exertion. These males owned nest boxes at which there were fewer visits by non‐pair males. Although females paired with dark mates worked less hard, they were able to raise more fledglings. Female oxidative damage measured as malondialdehyde (MDA) level in plasma declined with increasing incubation attendance and male incubation feeding. Moreover, levels of MDA in females declined with both darkness of male dorsal plumage and male forehead patch size when controlling for female forehead patch size and male age. The effect of male plumage darkness was especially strong. Females paired with middle‐aged males (2–3 yr) showed reduced levels of MDA compared with those paired with 1‐yr‐old and more than 3‐yr‐old males. Male age could not explain the effects of male attractiveness. Females paired with attractive males were more successful in reproduction while suffering reduced oxidative damage, possibly mediated by help during incubation and nestling rearing from their pair‐mates. Although correlative, the evidence suggests direct benefits of females paired with more attractive males.     

Dangerous love? Predation risk does not affect female mate choice in blue‐black grassquits

Predation risk may be an important factor affecting female mate choice. Hypothetically, females could choose extravagantly ornamented males that survive in high predation risk environments. However, this decision could be different if choosing a conspicuous male under high predation risk is costly for females or results in reduced offspring survival. In such contexts, females could become indifferent to male quality or prefer inconspicuous males. We tested this idea using captive blue‐black grassquits (Volatinia jacarina, Linnaeus, 1766), a species in which males perform conspicuous leap displays coupled with songs during the breeding season, which presumably subjects females and offspring to higher predation risk. Females were placed in an arena with speakers on opposite sides emitting male courtship songs. One speaker emitted songs at a high rate (proxy for a conspicuous male) while the other speaker broadcast songs at a low rate (proxy for a less conspicuous male). While the female evaluated the two male songs, a third speaker emitted vocalizations characterizing three levels of risk: adult predator, nest predator, and no‐risk control. Females showed no preference for either male stimuli across the predation risk treatments. This lack of preference relative to frequency of male vocal displays suggests that leap‐song frequency is not used by females during mate choice. We suggest that in addition to its role in courtship, male grassquit displays also signal status to other males when competing for territories. Thus, we propose that predation risk does not directly influence blue‐black grassquit intersexual selection and that females in this species may exercise indirect mate choice, choosing social mates based on male ability to establish and defend a territory, and relying secondarily upon other aspects of male display attributes, such as its visual components.     

The influence of parasites on host sexual selection

In 1982 Hamilton and Zuk(1) proposed a provocative solution for the unexplained fact that the males of many species exhibit 'showy' traits such as brightly coloured plumage or vigorous courtship displays. They suggested that showy traits are fully expressed only by males who are resistant to parasites and that females examine such traits in order to choose resistant males as mates. Hamilton and Zuk's proposal has been the topic of extensive research and vigorous debate for nearly a decade. This article reviews the research, relevant criticisms and unanswered questions pertaining to the influence of parasites on sexual selection.     

Functions of courtship feeding in black-legged kittiwakes: natural and sexual selection

Various authors have proposed that courtship feeding evolved under natural selection, sexual selection or both. Using observations of 250 breeding pairs over 3 consecutive years for a total of 77 000 nest-hours, we examined the functional significance of courtship feeding in a seabird, the black-legged kittiwake, Rissa tridactyla. We predicted courtship feeding would benefit males and females in different ways: males may invest in future progeny and females may allow copulations in exchange for food or use courtship feeding to assess males' parental quality. Courtship feeding was correlated with clutch size in 1 of 3 years, suggesting that males may increase their reproductive success by provisioning their mates. Courtship feeding, which was individually repeatable between years, was also related to male arrival date. These results suggest that courtship feeding is a reliable index of male quality that females may use for mate appraisal. Because courtship feeding commences after the pair bond is established, it cannot be used as a criterion for mate choice in the pair's first year. However, courtship feeding rate was related to male re-pairing success in the following breeding season. We thus suggest that courtship feeding in kittiwakes could have first evolved under natural selection (the nutrition hypothesis) and subsequently may have become a signal of male quality that females could use to evaluate their mates for future seasons (future mate appraisal hypothesis). Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Brood desertion and polygamous breeding in the Kentish Plover Charadrius alexandrinus

In the Kentish Plover Charadrius alexandrinus one of the adults, typically the female, deserts the brood when the chicks are a few days old. Once parental care is terminated, adults may initiate a second nesting attempt if sufficient time remains within the season. For these nests, individuals pair with different mates from those of the first nesting attempt, thus becoming sequentially polygamous. In a small population of Kentish Plovers in Fuente de Piedra lake (southern Spain), the duration of biparental care of broods was longer than in other localities. It also showed considerable variation between years that was evidently related to Gull-billed Tern Gelochelidon nilotica predation pressure on the chicks. There was year-to-year variation in the number of polygamous matings. Both the duration of the breeding season and nesting success in the first half of the season limited the occurrence of polygamy. Despite females deserting broods earlier than males, the interval between the first and second nesting of polyandrous females and polygynous males was similar. The interval was not affected by the body condition of females after the first nesting attempt, nor by problems related to egg formation ability, but was probably due to the availability of potential mates. More females than males initiated second nests, suggesting that polygamous opportunities were more limited for males than for females. In terms of delayed breeding, reduced survivorship or reduced breeding opportunities in years following polygamous breeding, polygamous individuals did not have greater costs than non-polygamous ones. Females with second nests did not seem to be selective in mate choice, mating with any available male. Mates for second nests may therefore be of lower quality than those for first nests, as judged by male plumage characteristics. Clutch sizes and egg characteristics of polyandrous females were similar in first and second nests. Nest success of second nests was only 40% of that of first ones, with nest desertion accounting for 60% of the losses. As the costs of polygamy are apparently low and as breeding success is very variable among years, polygamous breeding of the long-lived Kentish Plover may be an important breeding strategy with which to increase individual lifetime reproductive success.     

Fitness benefits of polyandry for experienced females

Females often mate with several different males, which may promote sperm competition and increase offspring viability. However, the potential benefits of polyandry remain controversial, particularly in birds where recent reviews have suggested that females gain few genetic benefits from extra‐pair mating. In tree swallows (Tachycineta bicolor), we found that females with prior breeding experience had more sires per brood when paired to genetically similar social mates, and, among experienced females, broods with more sires had higher hatching success. Individual females breeding in two consecutive years also produced broods with more sires when they were more genetically similar to their mate. Thus, experienced females were able to avoid the costs of mating with a genetically similar social mate and realize fitness benefits from mating with a relatively large number of males. This is one of the first studies to show that female breeding experience influences polyandry and female fitness in a natural population of vertebrates. Our results suggest that the benefits of polyandry may only be clear when considering both the number of mates females acquire and their ability to modify the outcome of sexual conflict.     

Castration in Gambel's and Scaled Quail: ornate plumage and dominance persist, but courtship and threat behaviors do not

During the breeding season, testosterone in male birds is often linked to some secondary sexual ornaments, courtship behaviors, and intrasexual aggression. I examined the effect of castration on plumage expression in Gambel's Quail (Callipepla gambelii), a species in which males are highly ornate, and in Scaled Quail (C. squamata), an unornamented species. Using male pairs, each consisting of a castrate and a control, I also assessed whether castration affected (1) the behavior of males, (2) the mating decisions of females, or (3) the outcome of male-male competition. Castration did not alter the plumage of male Gambel's or Scaled Quail. In these species, and some other members of the avian order Galliformes, production of ornate plumage appears to be independent of testosterone. In contrast, castration reduced or eliminated courtship behaviors. Females almost never preferred castrated individuals. During male-male competition, castrates also exhibited lower rates of threat behaviors, which appear to be identical to those used during courtship. Castration did not, however, influence the outcome of male-male competition. Castrates of both species exhibited overt aggression (pecks, chases, displacement) and frequently won male contests. Such results suggest that certain types of aggressive behavior may be testosterone-independent. In both Gambel's and Scaled Quail, male body size correlated positively with dominant individuals.     

Male and Female Soldier Beetles Relax Choice for Mate Quality Across Daily Courtship Periods

Mutual mate choice occurs when members of each sex will reject some potential mates in efforts to encounter better prospects later. The decision to reject may represent the interaction between mate preferences, mate availability, and temporal constraints. Theory predicts that mutual mate choice will favor relaxed choosiness as mate availability and time for courtship decline. We explored mutual mate choice in the soldier beetle, Chauliognathus pennsylvanicus (Cantharidae), where courtship consisted of males attempting to secure evasive females. We employed field observations, laboratory experiments, and stochastic simulations to investigate the decline in choosiness over the daily courtship period, during which individuals can mate at most once. We found that reproductive success of males and females increases with mate size and mating frequency. Females biased copulations toward larger mates by attempting to evade suitors, while males biased copulations by releasing the smaller females they capture. However, late in the day males and females may increase reproductive success by accepting rather than rejecting lower quality mates to maintain high mating rates. Stochastic simulations indicated that reproductive success, the product of mating frequency and mean mate size, was maximized in males and females by incrementally reducing mate standards across daily courtship periods. In the field, large males who rejected small females early in the daily courtship period rarely did so later. Large females used less effective evasive maneuvers later in the courtship period, resulting in copulations with progressively smaller males. These results support models of mutual mate choice that predict that individuals of high quality will maximize reproductive success by relaxing choosiness as the courtship period wanes.     

Re-use of courtship nests for quick remating in the polygynous Fan-tailed Warbler Cisticola juncidis

In a population of Fan-tailed Warblers Cisticola juncidis near Osaka, Japan, the males were polygynous, building a succession of elaborate courtship nests within their territories, and advertising them to females. Nest desertion by females frequently occurred early in the breeding cycle. Deserted nests were generally left untouched, but 17 out of 88 territorial males cleaned and re-used 20 of 79 nests deserted by females for their next courtship. The frequency of nest re-use increased with season. Of the re-used nests six (300%) were re-occupied by secondary females. Newly built nests were preferred to the 'second-hand' nests, probably because new nests were likely to last longer. Breeding success did not differ between the two categories of nests. In males, nest re-use seems to save time and energy expenditure for additional mating.     

Differences in potential reproductive rates of male and female seahorses related to courtship roles

Dwarf seahorses, Hippocampus zosterae (Syngnathidae), are distinguished by extreme morphological specialization for paternal care, the formation of monogamous pair bonds and mating repeatedly over the course of a breeding season. To determine the potential reproductive rates of male and female dwarf seahorses, we measured (1) the maximum number of offspring produced per breeding cycle when sexually receptive mates were unlimited, and (2) the relative time each sex was unavailable for mating ('time out'). We paired sexually isolated males and females with sexually receptive partners and observed them from the day of introduction through to copulation, to determine the length of time it takes each sex to prepare to mate. We conducted additional experiments to determine the length of gestation, which when added to the time needed to prepare to mate and copulate gives an estimate of total reproductive cycle duration, T. We estimated potential reproductive rate by dividing the mean number of offspring produced per breeding cycle by the duration of the breeding cycle (T). We estimated reproductive 'time out' by identifying the period of time males and females were physiologically capable of mating ('time in', S) and subtracting time S from time T. When provided with sexually receptive partners, females took 2 days longer than males to complete courtship and copulation, but neither males nor females remated during gestation. Therefore, males could potentially produce 17% more offspring than females over the course of one breeding season. Females had reproductive 'times out' 1.2 times longer than did males, as they were only capable of mating during the 4 h directly preceding copulation. Thus, H. zosterae males have higher potential reproductive rates and shorter reproductive 'times out' compared with H. zosterae females. These results and previous work indicating that seahorses display traditional courtship roles support the prediction that the sex having the higher potential reproductive rate, or equivalently, the shorter 'time out', will compete more intensely for access to the opposite sex. Copyright 2000 The Association for the Study of Animal Behaviour.     

Female extrapair mate choice in a cooperative breeder: trading sex for help and increasing offspring heterozygosity

Sexual conflict between males and females over mating is common. Females that copulate with extrapair mates outside the pair-bond may gain (i) direct benefits such as resources or increased paternal care, (ii) indirect genetic benefits for their offspring, or (iii) insurance against infertility in their own social mate. Few studies have been able to demonstrate the different contexts in which females receive varying types of benefits from extrapair mates. Here, I examined sexual conflict, female extrapair mate choice, and patterns of extrapair paternity in the cooperatively breeding superb starling Lamprotornis superbus using microsatellite markers. Although extrapair paternity was lower than many other avian cooperative breeders (14% of offspring and 25% of nests), females exhibited two distinct mating patterns: half of the extrapair fertilizations were with males from inside the group, whereas half were with males from outside the group. Females with few potential helpers copulated with extrapair mates from within their group and thereby gained direct benefits in the form of additional helpers at the nest, whereas females paired to mates that were relatively less heterozygous than themselves copulated with extrapair mates from outside the group and thereby gained indirect genetic benefits in the form of increased offspring heterozygosity. Females did not appear to gain fertility insurance from copulating with extrapair mates. This is the first study to show that individuals from the same population mate with extrapair males and gain both direct and indirect benefits, but that they do so in different contexts.