Female swamp sparrows do not show evidence of discriminating between the songs of peak‐aged and senescent males

Sexual selection theory predicts that females face contrasting selection pressures when choosing the age of their mate. On the one hand, older males have demonstrated their ability to survive and they may be more experienced than younger males. At the same time, however, younger males are expected to have accumulated fewer deleterious mutations in their germline as compared to older males. These contrasting pressures on female preference may result in a preference for intermediate‐aged males. A preference for males of a particular age can only be expressed, however, if females are able to identify males of different ages. We have previously shown that male swamp sparrows display age‐related changes in vocal quality, such that males display sharp increases in vocal quality in early adulthood, followed by gradual senescent declines thereafter. We have also shown that territorial males discriminate these within‐individual differences, giving stronger aggressive responses to songs of peak‐aged males than to those of senescent males. Here, we use a copulation solicitation assay to test whether females also discriminate these within‐signaler markers of senescence in song. Contrary to our prediction, females did not show any evidence of discriminating between songs recorded from peak‐aged males as compared to songs from the same males following song senescence. We suggest that this difference in demonstrated discrimination between males and females may be the result of the two sexes attending to different song characteristics.     

Blackcaps (Sylvia atricapilla) increase the whistle part of their song in response to simulated territorial intrusion

Bird song is a sexually selected signal that serves two main functions, attracting a mate and deterring rivals. Different signal parameters may be important in advertising to females compared to advertising to rival males. Species solve the problem of this dual function in a variety of ways, one of which may be to have separate parts of song directed at male and female receivers. The blackcap song has two distinct parts, a complex warble, assumed to be directed at female receivers, followed by a louder and more stereotyped whistle putatively directed at males. We simulated territorial intrusions by broadcasting blackcap song in territories. Comparing songs sung prior, with those produced in response to playback, showed that the proportion of the whistle component of songs increased, but not the warble. This study thus provides empirical evidence that the whistle component of the blackcap song plays a prominent role in male–male competition. The warble component of the blackcap song may be directed at females, but this requires further testing.     

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.     

Diet and birdsong: short‐term nutritional enrichment improves songs of adult Bengalese finch males

Song is a notable sexual signal of birds, and serves as an honest indicator of male quality. Condition dependence of birdsong has been well examined from the viewpoint of the developmental stress hypothesis, which posits that complex songs assure fitness because learned acoustic features of songs are especially susceptible to early‐life stress that young birds experience in song learning periods. The effect of early stress on song phenotypes should be crucial, especially in age‐limited song learners which sing stereotyped songs throughout life. However, little attention has been paid to non‐learned song features that can change plastically even in adulthood of age‐limited song‐learners. Although it has been shown that food availability affects song rate in wild songbirds, there is limited evidence of the link between favorable nutritional conditions and song phenotypes other than song rate. Under the prediction that singing behavior reflects an individual's recent life history, we kept adult Bengalese finch males under high‐nutrition or normal diet for a short term, and examined changes in body mass and songs. We found that birds on a high‐nutrition diet showed higher song output (e.g. song rate and length) compared with those of the control group, while changes in body mass were moderate. In addition, note repertoire became more consistent and temporal structures got faster in both nutrition and control groups, which indicates that songs were subject to other factors than nutrition. Considering that female estrildid finches, including Bengalese and zebra finches, show a preference toward complex songs as well as longer songs and higher song rate, it is plausible that different aspects of singing behavior signal different male qualities, and provide multifaceted clues to females that choose mates.     

Male House Finches with Elaborate Songs have Higher Reproductive Performance

The elaborate songs of male animals are thought to function in either territory defense (male–male communication) or mate attraction (male–female communication). In non‐territorial animals, male vocalizations are expected to function primarily in mate attraction, yet the reproductive consequences of male vocalizations in non‐territorial animals are poorly described. Here we explore the relationship between male song and male reproductive performance in a free‐living population of house finches, Carpodacus mexicanus, a non‐migratory, non‐territorial songbird. Based on recordings of 20 males, we analyzed three song features (song length, number of unique syllables per song, and song rate) and compared male song with two measures of within‐pair reproductive performance (nest initiation date and clutch size) and one measure of extra‐pair reproductive performance (whether males sired extra‐pair young). We demonstrate a positive association between male song and within‐pair reproductive performance; males that sang long songs initiated their first clutch significantly earlier and males that sang songs at a faster rate had larger clutches. Despite the fact that only one of our recorded males sired extra‐pair young in the nest of another male, this male's songs were the most elaborate for two of three song features measured, anecdotally suggesting that male song may play a role in both within‐pair and extra‐pair partner choice. These results suggest that male song is a sexually selected trait in non‐territorial house finches.     

Female dark‐eyed juncos Junco hyemalis thurberi produce male‐like song in a territorial context during the early breeding season

Reports of female song, once considered a rarity, have recently increased across a variety of avian taxa. Females of many species can be induced to produce male‐like song with exogenous testosterone, but observations of female song in free‐living birds remain limited by incomplete sampling of females. Here, we report three independent observations of female dark‐eyed juncos Junco hyemalis producing male‐like song early in the breeding season (i.e. post‐territory establishment, pre‐nesting) in a recently established non‐migratory, urban population. To elicit song, we presented 17 free‐living junco pairs with a live, caged female conspecific. Three unique females responded to our trials by diving at the intruding female, chasing their (male) mate, fanning their tail feathers, and singing a trilled song similar in structure to male long‐range (broadcast) song. We compared male and female songs quantitatively and found that the two sexes were statistically similar in many spectral and temporal characteristics, but female songs had significantly lower minimum and peak frequencies than males. This result is particularly surprising, as males in this urban population are known to sing at a significantly higher minimum frequency than males in a nearby montane population. Both the seasonal and social context in which these songs were observed suggest a potential function for female song in mate guarding and polygyny prevention, but more data are needed to test this hypothesis. Whether female song is common in all dark‐eyed juncos during the early breeding season or if it is restricted to this particular urban and non‐migratory population remains an important question for future research.     

Complementary neural systems for the experience‐dependent integration of mate‐choice cues in European starlings

Choice of a particular mate phenotype may arise out of experience with the very phenotypes under consideration. Female European starlings (Sturnus vulgaris) prefer males that sing predominantly long‐bout songs over males that sing predominantly short‐bout songs, and thus, song‐bout length is a phenotypic parameter instrumental in releasing the female's mate choice. The preferred long‐bout songs induce higher expression of the immediate early gene (IEG) ZENK in the female auditory telencephalon than short‐bout songs do, but this sensitivity to song length depends on the female's recent song experience. Here, we compared the experience‐dependent modulation of ZENK with that of another IEG, FOS, and report that ZENK and FOS expression in the caudomedial mesopallium and caudomedial nidopallium show different modulation properties that complement natural variation in song‐bout length. As reported previously, ZENK expression was greater in response to novel long‐bout than to novel short‐bout songs following a 1‐week experience with long‐bout but not short‐bout songs. In contrast, FOS expression was greater in response to novel long‐bout than to novel short‐bout songs following a 1‐week experience with short‐bout but not long‐bout songs. Thus, the ZENK and FOS signaling pathways are made sensitive to variation in song length by experiences with songs at opposite ends of the starling song‐variation continuum, suggesting the presence of complementary neural systems made sensitive in register with the natural axis of phenotypic variation fundamental to the female's mate choice. © 2004 Wiley Periodicals, Inc. J Neurobiol, 2005     

Grasshopper calling songs convey information about condition and health of males

Females of the grasshopper Chorthippus biguttulus invest much more in the offspring than do males. As a consequence, females are the more selective sex and exert a sexual selection on males by responding to the songs of certain conspecific males while rejecting others. What kind of information about the sender may a female obtain from a male’s song, in addition to its species identity? We searched for correlations between a series of song features and morphometric parameters of individual males. In addition, also the immunocompetence of males was assessed by implanting small pieces of nylon thread. We found significant, positive correlations between certain song characteristics and indicators of male size and immunocompetence. Thus, grasshopper females may—in principle—be able to judge a male’s condition and health from the acoustic signals he produces.     

Mate choice in Pied Flycatchers Ficedula hypoleuca: can females use song to find high‐quality males and territories?

High-quality male Pied Flycatchers Ficedula hypoleuca (defined by brighter plumage, better condition and more experience) have previously been shown to have larger syllable repertoires and greater song versatility than males of inferior quality. Thus, by preferring more complex songs, females could choose a high-quality male. Females may also use song as a cue to find a high-quality territory since early arriving males may obtain the best territories and these males have more complex songs than late-arriving males. We found that males with more complex songs had a greater chance of becoming paired and stayed unpaired for a shorter period than males with less elaborate songs. When controlling for arrival order, however, only strophe versatility was still correlated with pairing order. Males defending popular territories had more complex and longer songs and were also in better body condition than males in less popular territories. A multiple logistic regression showed that song length was important in explaining whether a male defended a popular nestbox or not. Thus, male arrival time seems to be important in deciding the quality of a male's territory, which in turn explains female choice. However, song quality seems to add important information. Thus, females could find both high-quality males and high-quality territories by using song cues during mate choice.     

Acoustic characteristics, early experience, and endocrine status interact to modulate female zebra finches' behavioral responses to songs

Female songbirds use male songs as an important criterion for mate selection. Properties of male songs are thought to indicate the male's quality as a potential mate. Song preferences in female zebra finches are known to be influenced by two factors--early auditory experience and the acoustic characteristics of males' songs. Studies often investigate song preferences by priming females with estrogen. However, estrogenic influences on song preferences have not been studied. We investigated the relative influence of early auditory experience, acoustic features of songs, and estrogen availability on song responsiveness in female zebra finches. Juvenile female zebra finches were tutored for 10 days with 40 songs per day with one of three acoustically different song types--simple songs, long-bout songs or complex songs. A fourth group of females was untutored. Aside from this brief song exposure, females were raised and maintained without exposure to male songs. During adulthood, females' behavioral responses to the three song types were tested under three hormone conditions--untreated, estradiol-treated and 1,4,6-androstatriene-3,17-dione (ATD)-treated (to lower endogenous estrogen). Based on the results of our study, four conclusions can be drawn. First, song responsiveness in female zebra finches is strongly affected by minimal early acoustic experience. Second, inexperienced female zebra finches are inherently biased to respond more to complex songs over other song types Third, although female zebra finches are inherently biased to respond more to complex songs, early acoustic experience may either reinforce or weaken this inherent responsiveness to complex songs. Fourth, estrogen selectively accentuates song responsiveness in acoustically-experienced female zebra finches.     

Polyandry enhances offspring viability with survival costs to mothers only when mating exclusively with virgin males in Drosophila melanogaster

A prominent hypothesis for polyandry says that male–male competitive drivers induce males to coerce already‐mated females to copulate, suggesting that females are more likely to be harassed in the presence of multiple males. This early sociobiological idea of male competitive drive seemed to explain why sperm‐storing females mate multiply. Here, we describe an experiment eliminating all opportunities for male–male behavioral competition, while varying females’ opportunities to mate or not with the same male many times, or with many other males only one time each. We limited each female subject's exposure to no more than one male per day over her entire lifespan starting at the age at which copulations usually commence. We tested a priori predictions about relative lifespan and daily components of RS of female Drosophila melanogaster in experimental social situations producing lifelong virgins, once‐mated females, lifelong monogamous, and lifelong polyandrous females, using a matched‐treatments design. Results included that (1) a single copulation enhanced female survival compared to survival of lifelong virgins, (2) multiple copulations enhanced the number of offspring for both monogamous and polyandrous females, (3) compared to females in lifelong monogamy, polyandrous females paired daily with a novel, age‐matched experienced male produced offspring of enhanced viability, and (4) female survival was unchallenged when monogamous and polyandrous females could re‐mate with age‐ and experienced‐matched males. (5) Polyandrous females daily paired with novel virgin males had significantly reduced lifespans compared to polyandrous females with novel, age‐matched, and experienced males. (6) Polyandrous mating enhanced offspring viability and thereby weakened support for the random mating hypothesis for female multiple mating. Analyzes of nonequivalence of variances revealed opportunities for within‐sex selection among females. Results support the idea that females able to avoid constraints on their behavior from simultaneous exposure to multiple males can affect both RS and survival of females and offspring.     

Attraction of Hoopoe Upupa epops females and males by means of song playback in the field: influence of strophe length

Experimental Hoopoe Upupa epops songs prepared with synthetic sound to differ in strophe length were used to test whether Hoopoe females prefer long strophes. The songs were broadcast simultaneously in the field from two loudspeakers situated 100 m apart, in early spring, when females actively search for mates. The playbacks attracted a total of 87 individuals, both males and females, with a maximum of five individuals (three males and two females) per trial. A female was considered to have been attracted by the song broadcast from a loudspeaker when she approached unaccompanied by a male, and when there was no male nearby. A total of 15 females chose one of the songs and significantly more were attracted by the one with long strophes. These results suggest that in the Hoopoe, male song attracts females, and that strophe length is a sexually selected song cue. There were no differences in the number or kind of males (classified according to strophe length) attracted by each playback. Frequently the experiment attracted more than one male simultaneously. These aggregations cannot be explained as territorial responses, and their significance is discussed together with that of natural spontaneous groupings of displaying males. Apparently males aggregate where they expect to find females.     

Behavioral responses of hybrid lacewings (Neuroptera: Chrysopidae) to courtship songs

The study of hybrid courtship songs and the behavioral responses of hybrids and parental individuals to hybrid songs can be useful in understanding the origin of reproductive isolation among species that differ mainly in their courtship songs. Here we test the hypotheses (a) that hybrid lacewings prefer hybrid songs to either of the parental songs from a cross betweenChrysoperla plorabunda andC. johnsoni, and (b) that parental individuals prefer their own song over those of hybrids. Analysis of songs showed that most features of hybrid songs are intermediate between the two parents. Hybrids organize their songs with a series of simple volleys like those ofC. plorabunda. Female hybrids from two reciprocal crosses and females and males of the parental species were presented with choices of hybrid and parental songs. Hybrids responded more to recordings of hybrid songs than to recordings ofC. plorabunda but did not differ in the responses given toC. johnsoni and hybrid songs. In contrast, males and females of both parental lines preferred to duet with recordings of their own song types and did not respond to hybrid songs. Our results demonstrate that hybrids would be at a disadvantage in nature, because neitherC. plorabunda norC. johnsoni will respond to their songs.     

Female choice for sick males over healthy males: Consequences for offspring

Sexual selection theory indicates that ornament expression in males is in close relation to their condition. This “honesty” relationship serves as the basis for female choice: Females would mate with healthy males over sick males after assessing male ornament signal expression and derive benefits for their progeny. Here, we investigated female mate choice for infected and non‐infected males, male survival after infection (to corroborate the negative effect of infection), and fitness consequences of female preferences using Tenebrio molitor beetles. Male infection was produced having two types of challenges as follows: males infected with entomopathogenic fungi and males infected with nylon implants. Similar to previous studies, we corroborated that females preferred fungus‐infected males over positive control, negative control, and nylon‐challenged males. Survival was the lowest for fungus‐treated males followed by nylon‐treated and control males. Females mated with fungus‐treated males laid fewer and smaller eggs, and the laid eggs had less lipid content with a reduced eclosion success compared to females mated with non‐challenged males. Our interpretation is that fungus‐treated males invested their energetic resources to increase their attractiveness at the risk of survival, in a terminal investment fashion. Females, however, would have corrected their choice by investing less in their offspring.     

Female life span and fertility are increased by the ejaculates of preferred males

In animals with internal fertilization, sperm competition among males can favor the evolution of male ejaculate traits that are detrimental to females. Female mating preferences, in contrast, often favor traits in males that are beneficial to females, yet little is known about the effect of these preferences on the evolution of male ejaculates. A necessary condition for female preferences to affect the evolution of male ejaculate characteristics is that females select mates based on a trait correlated with ejaculate quality. Previous work has shown that females of the variable field cricket, Gryllus lineaticeps, prefer males that produce calling songs containing faster and longer chirps. In this study, we tested the hypothesis that females receive more beneficial ejaculates from preferred males. Females were placed on either a high- or a reduced-nutrition diet then mated twice to a male of known song phenotype. Females received only sperm and seminal fluid from males during these matings. There was no effect of male song phenotype on any fitness component for females on the high-nutrition diet. Reduced-nutrition females mated to males that produced preferred song types, however, lived longer, produced more eggs, produced more fertile eggs, and had a higher proportion of their eggs fertilized than those mated to other males. The life-span benefit was positively associated with male chirp duration, and the reproductive benefits were positively associated with male chirp rate. We explored two possible mechanisms for the life span and reproductive benefits. First, a path analysis suggested that part of the effect of male chirp duration on female life span may have been indirect; females mated to males that produced longer chirps showed delayed oviposition, and females that delayed oviposition lived longer. Males that produce longer chirps may thus transfer fewer or less potent oviposition stimulants to females in their seminal fluid. Second, there was a positive correlation between male chirp rate and the number of sperm transferred to females. The fertility benefit may thus have resulted from females receiving more sperm from males that produce faster chirps. Finally, there was a negative phenotypic correlation between male chirp rate and chirp duration, suggesting that females may have to trade off the life span and reproduction benefits when selecting a mate.     

Female European starling preference and choice for variation in conspecific male song

Data from several field studies support the hypothesis that female European starlings, Sturnus vulgaris, attend to variation among the songs of conspecific males when making mate-choice decisions. However, for a variety of methodological reasons, direct evidence for female preferences based on song in starlings has been lacking. This study presents a novel technique for assaying directly female preference and choice in European starlings by using the presentation of conspecific male song as an operant reinforcer in a controlled environment. Using an apparatus in which the playback of songs from different nestboxes is under the operant control of the subject, we demonstrate how the reinforcing properties of conspecific song can be used to measure female preference and choice. The results of the study suggest three conclusions. First, female starlings prefer naturally ordered conspecific male songs over reversed songs. Second, female starlings display robust preferences for longer compared with shorter male song bouts. Behaviour in the operant apparatus varied directly with male song bout length. Third, preferences based on song bout length are sex specific. Male starlings failed to respond differentially to the same stimuli for which females showed strong preferences. These results suggest that male-male variation in song bout length is important for mate choice among starlings. In addition, we detail the use of a novel behavioural assay for measuring female preferences that can be applied to similar behaviours in other species of songbirds. Copyright 2000 The Association for the Study of Animal Behaviour.     

Variation and consistency of female preferences for simulated courtship songs in Drosophila virilis

To study the variation and consistency of song preferences in Drosophila virilis females, we played them species-specific song and songs with modified sound pulses and/or interpulse intervals on 3 consecutive days. Species-specific song was played again on the fourth day. All playbacks were done without the presence of males. About 62% of the females indicated their readiness to mate by spreading their wings in at least one of the trials. The proportion of the females responding to species-specific song was about twice that of the females responding to modified songs. The majority of females responded to only one song type, which suggests that the females varied in their preferences and that their preference windows were rather narrow. The females were consistent in their responsiveness to species-specific song played on 2 days. If the female responded to normal song during the first trial, the probability of her responding to the same song during the second trial increased by about 32%. The number of songs required by the females before responding in the two subsequent trials was also correlated within the females (repeatability 0.328). Repeatability of female preferences for male sexual traits is expected both in the viability and Fisherian models of sexual selection. Copyright 1999 The Association for the Study of Animal Behaviour.     

Whip it good! Geographic consistency in male songs and variability in female songs of the duetting eastern whipbird Psophodes olivaceus

Geographic variation in male bird songs has been studied extensively, but there have been few investigations of geographic variation in female songs or sex differences in patterns of geographic variation. We compared patterns of variation in male and female songs of eastern whipbirds Psophodes olivaceus by analyzing recordings from 16 populations across the species’ geographic range in eastern Australia. We found remarkably different patterns of geographic variation between the sexes. Female eastern whipbird songs are easily categorized into discrete song types. Song types are shared between nearby females, but female songs show pronounced differences at a continental scale. In contrast, male eastern whipbird songs show high consistency throughout the species’ geographic range. All recorded males share the ability to transpose the frequency of the introductory whistle and most recorded males share the ability to vary the direction of the slope of the terminal whip crack. For eight of nine measured variables, female songs show significantly higher levels of variation than male songs. We discuss whether sex differences in dispersal, song learning strategies, and song function may explain these sex differences in patterns of song variation. We suggest that eastern whipbirds have experienced a decoupling of male and female song learning strategies and that the songs of each sex have responded to different selective pressures in the context of countersinging interactions. We speculate that consistency in male songs throughout the geographic range of eastern whipbirds may arise through female preference for males that perform large bandwidth whip cracks.     

False promises: females spurn cheating males in a field cricket

Females commonly prefer to mate with males that provide greater material benefits, which they often select using correlated male signals. When females select higher-benefit males based on correlated signals, however, males can potentially deceive females by producing exaggerated signals of benefit quality. The handicap mechanism can prevent lower-quality males from producing exaggerated signals, but cannot prevent cheating by higher-quality males that choose to withhold the benefit, and this poses a major problem for the evolution of female choice based on direct benefits. In a field cricket, Gryllus lineaticeps, females receive seminal fluid products from males with preferred songs that increase their fecundity and lifespan. We tested the hypothesis that female behaviour penalizes males that provide lower-quality benefits. When females were paired with males that varied in benefit quality but had experimentally imposed average songs, they were less likely to re-mate with males that provided lower-quality benefits in the initial mating. This type of conditional female re-mating may be a widespread mechanism that penalizes males that cheat on direct benefits.     

Watch Your Tone: Social Conditions Modulate Singing Strategies

Bird song is typically depicted as a male singing a long‐distance signal to potentially unknown receivers to (1) deter males and (2) attract females. Nevertheless, many songbirds sing from close distances to a known receiver; males of these species may be under more intense selective pressure to modify their songs depending on the sex of the receiver in order to convey different motivational states (aggression versus courtship) to the different sexes. In a laboratory setting, we examined how receiver sex affected within‐song variation of the close‐range singing behavior in the brown‐headed cowbird (Molothrus ater). Although we know that cowbird song is influenced by flock composition, it is still unclear as to how the cowbird modifies his song based on social context. Using a cross‐correlation analysis of each male's different song types, we found that pairs of songs were significantly more dissimilar if they were directed to females compared with songs directed to males. We subsequently tested whether there were any consistent spectral or temporal patterns in the songs males gave to females versus to males. Our results lend support for the Motivational Structural Rules Hypothesis as songs directed toward males had higher entropy (i.e., harshness) than the same song type directed toward females. Our results suggest that cowbirds may have evolved the ability to alter multiple dimensions of their singing behavior based on receiver sex.