Assortative mating by white-crowned sparrows at song dialect boundaries

We tested the hypothesis that female Nuttall's white-crowned sparrows (Zonotrichia leucophrys nuttalli) mate assortatively with males from the same dialect population. Young birds of both sexes learn their natal dialect during an early sensitive period, and for females, this early experience may be the basis of future mate choice. A total of 32 female sparrows were mist-netted for three experiments at or near dialect boundaries just inside the Limantour, Drake and Clear dialect populations in Marin Co., California. The mates of all captured females sang the home dialect. All females were implanted with testosterone and maintained in captivity. Of the females which began to sing, 25 sang recognizable white-crowned sparrow songs. Of those 25 females, 24 had mated assortatively, thus supporting the assortative mating hypothesis.     

Social factors affect the singing rates of female northern cardinals Cardinalis cardinalis

Social factors, such as the duration of territorial occupancy or of time paired with a mate can affect the rate at which individual birds sing. This study examined the influence of duration of pair-bond and territory occupancy as well as date on the rate of singing by male and female northern cardinals Cardinalis cardinalis . When differences in breeding status were controlled, female cardinals sang at higher rates earlier in the season. Females in newly formed pairs sang at significantly higher rates than those in pairs that had previously bred together. In contrast, male cardinals did not show significant variation in the rate of singing throughout the season. The song rates of males in newly formed and established pairs did not differ significantly. Song rates for males and females in mated pairs were not significantly correlated. This study suggests that social factors have a strong effect on the rate at which female cardinals sing. It is possible that increased intra-sexual aggression by females when they are establishing a new territory with a new mate leads to this higher level of song output. Once females have established a territory and acquired a mate, dear-enemy effects might diminish the need for acoustic territorial defence. Differences in the constraints of nesting or the attraction of extra-pair mates might explain the sexual differences in male and female singing behaviour.     

Social factors affect the singing rates of female northern cardinals Cardinalis cardinalis

Social factors, such as the duration of territorial occupancy or of time paired with a mate can affect the rate at which individual birds sing. This study examined the influence of duration of pair‐bond and territory occupancy as well as date on the rate of singing by male and female northern cardinals Cardinalis cardinalis. When differences in breeding status were controlled, female cardinals sang at higher rates earlier in the season. Females in newly formed pairs sang at significantly higher rates than those in pairs that had previously bred together. In contrast, male cardinals did not show significant variation in the rate of singing throughout the season. The song rates of males in newly formed and established pairs did not differ significantly. Song rates for males and females in mated pairs were not significantly correlated. This study suggests that social factors have a strong effect on the rate at which female cardinals sing. It is possible that increased intra‐sexual aggression by females when they are establishing a new territory with a new mate leads to this higher level of song output. Once females have established a territory and acquired a mate, dear‐enemy effects might diminish the need for acoustic territorial defence. Differences in the constraints of nesting or the attraction of extra‐pair mates might explain the sexual differences in male and female singing behaviour.     

Delayed vocal ontogeny in songbirds: a laboratory study validates a model for delayed development derived from field studies

Based on field studies, we proposed a model that describes how vocal ontogeny proceeds over a 2-year period in wild brown-headed cowbirds (Molothrus ater). We tested this model in the laboratory by exposing yearling male cowbirds (n?=?7 tutees), trapped at the start of the breeding season in a southern California dialect, to adult tutors with unfamiliar song types from a different dialect. As adults at the start of their second season, the tutees all had enlarged repertoires based almost entirely on tutor song types. Thus, tutees dropped song types in their yearling repertoires that did not match tutor types and added tutor songs that they had heard for the first time as yearlings in captivity. We discuss these findings in the context of a previous captivity study in which tutees also changed their yearling repertoires but generally failed to copy their tutors’ songs. This is the first laboratory study to fully replicate the delayed ontogeny we have described for wild cowbirds, and validates the delayed vocal development model we proposed. This model is important in a more general context, because it explains how song dialects can remain temporally stable despite immigration by young males with non-local songs.     

Song-rates and parental care by individual male stonechats (saxicola torquata)

During their pre-breeding song period, male stonechats (Saxicola torquata) varied widely in rates of song production. Unpaired males sang more than males associated with females. Song-rates were significantly correlated with later participation in parental care, measured as the share taken, relative to their mate's share, in feeding nestlings, and defending them from predators by warning and distraction displays. Males that sang most did not consistently have the best breeding performance. The implications of these results for the use of male song in mate selection by females are discussed.     

Acoustic courtship signals in the Caribbean fruit fly, Anastrepha suspensa (Loew)

Male Caribbean fruit flies, Anastrepha suspensa (Loew) produce two sounds in sexual contexts, calling songs and precopulatory songs. Calling song occurs during pheromone release from territories within leks and consists of repeated bursts of sound (pulse trains). Virgin female A. suspensa became more active in the presence of recorded calling songs. Activity during the broadcast of a heterospecific song did not differ from movement during periods of silence. A conspecific song typical of smaller males, i.e. conspicuous for its long periods between pulse trains, also failed to elicit more activity by virgin females than silence. Mated females were most active during silences. Unmated males had no obvious reaction to sound. Calling songs are apparently sexually important communications which females discriminate among and may use as cues for locating and/or choosing between mates. Precopulatory song is produced by mounted males just before and during the early stages of copulation. Males that did not produce such songs remained coupled for shorter periods, perhaps passing fewer sperm. Wingless (muted) males were more likely to complete aedeagal insertion if a recorded precopulatory song was broadcast. Calling song played at the same level (90 dB) had no significant effect on the acceptance of males, nor did precopulatory song at a lower SPL (52dB). Precopulatory song may be used to display male vigour to choosing females.     

Male song diversity and its relation to breeding success in southern house wrens Troglodytes aedon chilensis

Theory proposes an adaptive relationship between male song complexity, including large song repertoires, and improved breeding success. Evidence supporting these relationships exists but is sometimes mixed or weak. Here we provide a first comprehensive study of the relationship between male song diversity and breeding success in a non‐migratory, austral population of house wrens Troglodytes aedon chilensis breeding in Mendoza, Argentina. During a two‐year field study, we measured breeding success for a population of 62 males and recorded more than 34 000 songs from a subsample of 26 males. For the latter subsample, we tested for correlations between six measures of song diversity and four canonical measures of annual breeding success. Males that sang with greater overall syllable type diversity and that had larger song repertories paired with females that bred earlier and laid more eggs over the course of the breeding season. However, these males also showed lower levels of immediate song type diversity, as measured by the Levenshtein distance between successive songs. We discuss implications for the evolution of song complexity in this exceptionally widespread species and the selective mechanisms that might influence song complexity in resident populations in the Neotropics compared to migratory populations in the northern hemisphere.     

Song overproduction, selective attrition and song dialects in the white-crowned sparrow

Male Puget Sound white-crowned sparrows, Zonotrichia leucophrys pugetensis, form large vocal dialects along the Pacific northwest coast of North America. Most adult males sing a single song dialect throughout their lives. To determine how dialects are maintained in this species, I studied two populations at the Columbia River mouth in a contact zone between two dialects. Singers of each of the two dialects clustered together in space, forming local song 'neighbourhoods'. Two hypotheses for the maintenance of dialects were tested. The late acquisition hypothesis predicts that yearling or adult male immigrants memorize their song from the territory neighbours they settle next to. The selective attrition hypothesis predicts that males memorize a variety of dialects early in life, overproduce song dialects upon arrival, and later selectively retain the one prelearned dialect that best matches what their neighbours sing. In 1997 and 1998, 35-40% of new territory occupants sang two dialects upon arrival in April, and then over the course of days to several weeks, discarded one dialect from their repertoire. Fourteen of 16 (88%) kept as their adult song the dialect that matched the dialect sung by the majority of their neighbours. No male added a new dialect to his repertoire after arrival, nor did males alter their retained dialect to more closely resemble their neighbours' songs. New arrivals that overproduced dialects upon arrival were significantly more likely to match their neighbours' dialect than males that did not overproduce upon arrival. In a playback experiment, males in the overproduction stage engaged in matched countersinging to the dialect played to them. These observations and the experiment support the selective attrition hypothesis: males visit and memorize a variety of dialects, probably in their hatching-year summer, overproduce dialects upon arrival the next spring, and then selectively retain the one dialect that matches the local song culture. Vocal plasticity late in life is not the result of a late sensitive phase for song memorization, but rather results from behavioural selection operating on a pre-existing repertoire of song dialects. Copyright 2000 The Association for the Study of Animal Behaviour.     

Rufous‐capped Warblers Basileuterus rufifrons show seasonal,temporal and annual variation in song use

In the majority of songbird species, males have repertoires of multiple song types used for mate attraction and territory defence. The wood‐warblers (family Parulidae) are a diverse family of songbirds in which males of many migratory species use different song types or patterns of song delivery (known as ‘singing modes’) depending on context. The vocal behaviour of most tropical resident warblers remains undescribed, although these species differ ecologically and behaviourally from migratory species, and may therefore differ in their vocal behaviour. We test whether male Rufous‐capped Warblers Basileuterus rufifrons use distinct singing modes by examining song structure and context‐dependent variation in their songs. We recorded multiple song bouts from 50 male Warblers in a Costa Rican population over 3 years to describe seasonal, diel and annual variation in song structure and vocal behaviour. We found that Rufous‐capped Warbler songs are complex, with many syllable types shared both within and between males’ repertoires. Males varied their song output depending on context: they sang long songs at a high rate at dawn and during the breeding season, and shortened songs in the presence of a vocalizing female mate. Unlike many migratory species, Rufous‐capped Warblers do not appear to have different singing modes; they did not change the song variants used or the pattern of song delivery according to time of day, season or female vocal activity. Our research provides the first detailed vocal analysis of any Basileuterus warbler species, and enhances our understanding of the evolution of repertoire specialization in tropical resident songbirds.     

Effects of location in territory and distance from neighbours on the use of song repertoires by Carolina wrens

By capturing territorial Carolina wrens (Thryothorus ludovicianus) and housing them in portable cages on their territories, I could control each one's location in its territory and distance from neighbours in experiments on the use of song repertoires. Experiment 1 demonstrated that these wrens sang more songs in the centre of their territories than at the edge, but that they did not use more song types or different song types at the centre than at the edge. In experiment 2, in which I played tape-recorded songs at two distances from wrens caged in the centres of their territories, birds responded more strongly to songs at 25m, simulating an intruder, than to songs at 165 m, simulating a territorial neighbour. Birds also switched more frequently between song types and sang more song types per 100 songs in response to the nearer playback. Experiment 3 compared captive wrens 140 m, 80 m, 20 m, or 0 m apart on adjacent territories. As the distance between neighbours decreased, birds sang less, but also switched more frequently between song types, used more song types per 100 songs, and matched songs with neighbours more frequently. There were no differences in the kinds of song types sung at different distances from neighbours. A comparison of the results from experiments 1 and 3 confirms that the use of song repertoires is influenced by distance from conspecifics and not by location in the territory.     

Acoustic mate copying: female cowbirds attend to other females' vocalizations to modify their song preferences

We conducted a tutoring experiment to determine whether female brown-headed cowbirds (Molothrus ater) would attend to vocalizations of other females and use those cues to influence their own preferences for male courtship songs. We collected recordings of male songs that were unfamiliar to the subject females and paired half of the songs with female chatter vocalizations—vocalizations that females give in response to songs sung by males that are courting the females effectively. Thus, chatter immediately following a song provided a cue indicating that the song was sung by a male who was of high-enough quality to court a female successfully. Using a cross-over design, we tutored two groups of females with song–chatter pairings prior to the breeding season. In the breeding season, we placed the tutored females into sound-attenuating chambers and played them the same songs without the chatter. Females produced significantly more copulation solicitation displays in response to the songs that they had heard paired with chatter than to songs that had not been paired with chatter. This experiment is the first demonstration that females can modify their song preferences by attending to the vocal behaviour of other females.     

Geographic variation in bird songs: examination of the effects of sympatric related species on the acoustic structure of songs

Birdsong evolution has influenced by various ecological and social factors. When related species that sing similar songs coexist, the acoustic properties of the songs of one or both species may shift, and the songs may diverge. We investigated geographic variation in the songs of the Japanese tit (Parus minor) and the varied tit (Poecile varius) in the Ryukyu Archipelago, Japan, whose islands harbor either one or both species. The songs of the two species exhibited similar structure, but acoustic measurements differed between them. For example, varied tits sang songs at higher frequency than Japanese tits did. The songs of both species varied geographically. At sites with higher relative densities of varied tits, Japanese tits sang lower frequency songs, indicating that in areas of coexistence, Japanese tits sang songs that had acoustically diverged from those of varied tits. Song variation in varied tits was not related to sympatry with Japanese tits. These asymmetric results suggest that the subordinate Japanese tit modified the acoustic characteristics of its song to avoid harassment by the dominant varied tit. We observed no effects of genetic divergence or local intraspecific density on Japanese tit or varied tit songs. This study used geographic variation to examine hypotheses of song evolution, and the results highlight the importance of character displacement.     

Song variation in insular and mainland California Brown Creepers(Certhia familiaris)

Summary Songs of Brown-Creepers(Certhia familiaris) in California were studied. Each individual usually sang one theme. Two geographic groups of songs were described which were designated the northern and southern dialects. These songs differed in the morphology of the introductory and terminal syllables. The northern dialect is currently known to extend from Point Reyes to the City of San Francisco, and includes birds from east San Francisco Bay. The southern dialect ranges from Carmel and Point Lobos to Morro Bay. Birds from the Hastings Reservation, 30 miles inland, sang the southern dialect. Creepers on Angel Island exhibited the typical island phenomenon of simpler structure but greater individual variability. We suggested that lack of social interaction due to dispersed habitat has contributed to these song changes. California Creeper songs are more variable with regard to note sequencing than those of their European congeners.

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Gesangsunterschiede bei kalifornischen Waldbaumläufern zwischen Insel- und Festlandspopulationen

Zusammenfassung Der Gesang des Waldbaumläufers(Certhia familiaris) in Kalifornien wurde untersucht. Jedes Individuum verfügt gewönhlich nur über eine Strophe. Es werden zwei geographische Formen des Gesangs beschrieben, die als nördlicher und südlicher Dialekt bezeichnet werden. Sie unterscheiden sich im Aufbau der einleitenden und der Schlußelemente. Der nördliche Dialekt reicht nach dem gegenwärtigen Stand der Kenntnis von Point Reyes bis in die Innenstadt von San Francisco. Er wird auch von Tieren auf der Ostseite der Bucht von San Francisco gesungen. Der südliche Dialekt reicht von Carmel und Point Lobos bis nach Morro Bay. Tiere in der Hastings Reservation, etwa 30 Meilen landeinwärts, sangen ebenfalls den südlichen Dialekt. Die Baumläufer der Insel Angel Island zeigen den typischen Inseleffekt: Ihr Gesang ist durch einen einfacheren Aufbau, aber durch größere individuelle Variabilität gekennzeichnet. Diese Veränderung des Gesanges gegenüber den Festlandspopulationen ist wahrscheinlich auf die Tatsache zurückzuführen, daß zwischen den einzelnen Männchen der Inselpopulation, die weit auseinanderliegende Baumgruppen bewohnen, kein oder wenig akustischer Kontakt besteht. Ganz allgemein sind die kalifornischen Waldbaumläufer in ihrer Lautfolge variabler als ihre europäischen Artgenossen.

     

Validating the female bioassay of cowbird song: Relating differences in song potency to mating success

Female cowbirds (Molothrus ater), maintained in isolation from males during the breeding season, respond to the playback of male song with copulatory postures. They respond more often to some songs than others. Song potency can thus be operationally defined by the number of copulatory responses a song elicits. The purpose of the present study was to validate this measure of song potency by investigating its relationship to mating success. We observed two colonies of cowbirds during the breeding season and recorded details of their courtship. In addition, song potency of the males was tested by playback with a different group of captive females. The results indicate a relationship between maximum song potency and mating success: the males that obtained the most copulations had songs of higher maximum potency and were also observed to have been more dominant during the winter and early spring.     

Physically Challenging Song Traits,Male Quality,and Reproductive Success in House Wrens

Physically challenging signals are likely to honestly indicate signaler quality. In trilled bird song two physically challenging parameters are vocal deviation (the speed of sound frequency modulation) and trill consistency (how precisely syllables are repeated). As predicted, in several species, they correlate with male quality, are preferred by females, and/or function in male-male signaling. Species may experience different selective pressures on their songs, however; for instance, there may be opposing selection between song complexity and song performance difficulty, such that in species where song complexity is strongly selected, there may not be strong selection on performance-based traits. I tested whether vocal deviation and trill consistency are signals of male quality in house wrens (Troglodytes aedon), a species with complex song structure. Males’ singing ability did not correlate with male quality, except that older males sang with higher trill consistency, and males with more consistent trills responded more aggressively to playback (although a previous study found no effect of stimulus trill consistency on males’ responses to playback). Males singing more challenging songs did not gain in polygyny, extra-pair paternity, or annual reproductive success. Moreover, none of the standard male quality measures I investigated correlated with mating or reproductive success. I conclude that vocal deviation and trill consistency do not signal male quality in this species.     

Ecological effects on song learning: delayed development is widespread in wild populations of brown-headed cowbirds

The timing and extent of early exposure to conspecific song can have critical influence on subsequent male vocal development in songbirds. Opportunities to memorize local song models may vary among populations depending on local ecological conditions that determine the length of the breeding season. In populations with comparatively short breeding seasons, such as northern or high-elevation populations, restricted access to local songs may delay development in a large proportion of juveniles. Previous studies have described extreme examples of delayed development in high-elevation populations of brown-headed cowbirds, Molothrus ater, in the Sierra Nevada of California, U.S.A. In the current study, we determined that delayed development also occurs in a low-elevation population located at a more northerly latitude than those in the Sierra. We recorded two kinds of songs from yearling and adult males who had been given testosterone (testosterone increased song output but did not change the nature of songs in males' repertoires) soon after being trapped at two adjacent sites in New York state, U.S.A. The average size of ‘perched’ song repertoires of 17 yearlings was significantly smaller than that of 20 local adults (2.8 versus 4.6 types, respectively) and yearlings generally lacked the shared songs typically found in adult repertoires. Only 40% of yearlings trapped at one site produced the correct local dialect ‘flight whistle’ compared with 91.7% of adults. These results strongly suggest that juvenile access to local songs is also restricted in this population and that delayed vocal development is widespread in cowbirds. In addition, these findings indicate that reliance on field recordings may underestimate adult-yearling differences in vocal competency in cowbirds because yearlings that sing readily in nature may not be representative of yearlings in general, a result that may also apply to other songbird species.     

Female choice for song characteristics in the house finch

Song has been proposed to function in mate choice, and such a role has been demonstrated experimentally in a number of species. We presented captive female house finches, Carpodacus mexicanus, with a choice of two songs, each of which was identical except for a single parameter that had been either accentuated or minimized. To ensure that our playback tapes offered choices within the normal range of variation in house finch song, we recorded wild male finches, then created playback tapes using values for the song parameters under consideration that were above or below the mean for the local population, but within the natural range of variation. We presented females that had not previously mated with choices between songs that (1) were long or short, (2) were given at fast or slow rates, and (3) included a large or small repertoire of unique song elements. Females showed significant preferences for long songs and for songs presented at a faster rate, but there was no significant preference for large or small repertoires of unique song elements. Song length and rate each seem likely to indicate a male's energy reserves, and thus could be important sources of information for females choosing mates.     

Nonlocal male mountain white-crowned sparrows have lower paternity and higher parasite loads than males singing local dialect

Bird song often varies geographically, and when this geographicvariation has distinct boundaries, the shared song types arereferred to as song dialects. We investigated the role of songdialect in male mating success in a wild breeding populationof mountain white-crowned sparrows (Zonotrichia leucophrysoriantha). In 2 of 3 years, males singing unusual songs ("nonlocal"males) had lower total fertilization success (measured by microsatellitepaternity analysis) than did males singing the local dialect ("local" males). Similarly, females produced disproportionately more young with local than with nonlocal males. However, dialectwas not a significant predictor of male mating success whencontrolling for other factors that might affect paternity.Instead, the low mating success of nonlocal males was apparentlydue to an interaction between song dialect and parasite load.Nonlocal males were more severely infected by bloodborne Haemoproteusthan were local males, although they did not differ in anyother measured aspect of quality. Immigrant birds may be immunologically disadvantaged, possibly due to a lack of previous experiencewith the local parasite fauna, resulting in low mating success.     

Singing by male and female Kloss gibbons (Hylobates klossii) in the Peleonan Forest, Siberut Island, Indonesia

Kloss gibbons (Hylobates klossii) are endemic to the Mentawai Islands in Indonesia and are one of only two gibbon species in which mated pairs do not sing duets. This is the first long-term study of the factors influencing the singing activity of Kloss gibbons within a northern Siberut Island population and follows two previous studies in central Siberut nearly 30 years ago. We collected data on the presence/absence of male and female singing within the study area on 198 days and within a focal group on 47 days. Rainfall during the time period in which they normally sing inhibits singing in both males and females. Our study supports the hypothesis that male and female songs function in intrasexual resource defence, as singing is associated with singing by same-sex neighbours, and same-sex choruses are more likely to occur after one or more days of silence (from that sex), suggesting there is pressure for individuals to communicate with same-sex neighbours regularly. Singing was not coordinated within a mated pair, suggesting that vocal coordination of the pair has been lost with the loss of the duet and that Kloss gibbon songs do not convey information to neighbours about the strength of the pair bond. On days when males sang predawn, females were more likely to sing after dawn and earlier in the morning. Additionally, the number of groups singing in female choruses was positively associated with the number of males that had sung in the predawn male chorus. We suggest that female songs have an intersexual territory defence as well as an intrasexual function.