Song repertoire size and female preferences in song sparrows

Summary Captive female song sparrows (Melospiza melodia), after treatment with estradiol, perform copulation solicitation displays when presented with songs of conspecific males. Females respond more strongly to eight song types than to four, and to sixteen song types than to eight. These results are consistent with the hypothesis that female song sparrows prefer large repertoires, rather than preferring normal or natural repertoire sizes (5 to 13 song types).The results with captive females might be taken to imply that females in the field prefer as mates those males with the largest repertoire sizes. This hypothesis was tested by observing pairing in a field population. In each of 2 years, there was no significant correlation between male repertoire size and date of initial pair formation. Furthermore, there was no correlation between repertoire size and the speed with which a second mate was acquired after removal of the first. It is concluded that repertoire size does not have an important influence on female choice of mates in song sparrows.     

Culturally correct song dialects are correlated with male age and female song preferences in wild populations of brown-headed cowbirds

Variation in vocal behavior among local populations of songbirds may be significant to females in mate choice. In a study of dialect populations of brown-headed cowbirds, estradiol-implanted females from two dialects held the pre-copulatory lordosis posture longer in response to playback of the local flight whistle song than to foreign whistle types from adjacent and more distant dialects. Females were held in captivity for a relatively brief period prior to testing and received no tutoring so discrimination was based solely on experience in the wild. This is the first study to show evidence of discrimination by female cowbirds based on flight whistle type. Evidence is presented from one of the study dialects that the majority of yearling male cowbirds are vocally distinct from resident adults in having either foreign or incomplete local whistles. Although these yearlings are fully mature sexually, they have little or no mating success. The correlation between female whistle preference and male mating success suggests that the ability to give the correct local whistle type may be a characteristic used by females to assess age and quality of a potential mate. A learned female preference for the predominant local song type may be a factor in the stability of these dialects by making it adaptive for males to conform to the local dialect.     

Song sharing correlates with lifetime social pairing success but not territory tenure in the Puget Sound white-crowned sparrow

Imitative song learning in birds often results in the formation of vocal dialects or local song neighborhoods in which males in close proximity share very similar songs. If song sharing confers a selective advantage due to intra-sexual competition or inter-sexual mate choice, song sharing should enhance the singer’s territory tenure or lifetime pairing success. We tested this in a migratory population of the Puget Sound white-crowned sparrow, Zonotrichia leucophrys pugetensis, in which some territory neighbors share whole songs. Song sharing with territory neighbors in the first year on territory did not correlate with territory tenure but correlated positively with social pairing success throughout a male’s lifetime when length of territory tenure was controlled. Thus, song sharing in this migratory population does not appear to confer a benefit in male–male interactions, at least as measured by the length of territory tenure. However, males that share songs do benefit from higher lifetime pairing success. Combined with the data available for other species, it appears that intra- and inter-sexual selection may have stronger effects on song sharing in sedentary and migratory populations, respectively.     

The behavioral response of female Nuttall's White-crowned Sparrows to male song of natal and alien dialects

Summary Female Nuttall's White-crowned Sparrows (Zonotrichia leucophrys nuttalli) were tested in a laboratory experiment to determine their response to stimulation by songs from their natal dialect (Clear) and by songs from three different alien dialects (Fig. 1). The greatest number of copulation solicitation displays and amount of locomotor activity were caused by songs of the subject's natal dialect (Clear); the next most potent stimulus was the contiguously adjacent dialect (Buzzy); the least effective stimuli were songs from a dialect 25 km distant (McClure), representing the same non-migratory subspecies, and a dialect 1,900 km distant (Sand Creek), representing a migratory montane subspecies of White-crowned Sparrow (Figs. 2–4).These results constitute a test of a deduction made from the assortative mating theory and suggest that female White-crowned Sparrows find male song of their natal dialect sexually more stimulating. Thus, speculating about the natural circumstances, females given an unrestricted choice would be expected to mate with males from their natal dialect region.     

The response of female Mountain White-crowned Sparrows to songs from their natal dialect and an alien dialect

Summary Female Mountain White-crowned Sparrows from Colorado were tested in a laboratory playback experiment to determine their response to male songs from their own natal dialect and to those from an alien dialect of the same subspecies, Zonotrichia leucophrys oriantha (Fig. 1). Observations were made on locomotor activity and copulation postures produced during each experimental test session.The subjects gave copulation displays almost exclusively when hearing their natal dialect and new or no displays when hearing the alien dialect (Fig. 2). The birds also exhibited significantly greater locomotor activity when hearing the natal dialect than they did when hearing the alien dialect (Fig. 3).We conclude that females are sensitized by their early song learning experience to be responsive to songs from their natal dialect and virtually sexually unresponsive to songs from an alien dialect. We speculate that the copulation posture given in the experiment implies that females in natural populations would preferably only mate assortatively with males from their natal dialect region.     

Do male plumage and song characteristics influence female off-territory forays and paternity in the hooded warbler?

Extra-pair fertilizations are common in many socially monogamous species, and paternity studies have indicated that females may use male vocal performance and plumage ornaments as cues to assess male quality. Female off-territory forays may represent a key component of female choice and male extra-pair mating success, and female foray behaviour is expected to be strongly influenced by indictors of male quality. In this study, we examined how male song and ornamentation affect how often females left their territories, which males they visited and extra-pair paternity in a socially monogamous passerine, the hooded warbler (Wilsonia citrina). We radiotracked 17 females during the fertile period and quantified male vocal performance (song output and rate) and plumage characteristics (size of the black melanin hood and colour of the black hood, yellow cheeks and breast areas). We obtained blood samples and determined paternity at 35 nests including those of 14 females that we radiotracked. Eleven (65%) of the 17 females forayed off-territory, whilst fertile and female foray rate was positively correlated with the number of extra-pair young in the nest. Females that left their territories more frequently were paired with males that sang at a low rate. In addition, extra-pair mates had higher song rates than the social mates they cuckolded (5.3 songs/min vs. 4.4 songs/min). Female off-territory forays or extra-pair paternity were not significantly related to male plumage characteristics. Our results indicate that a high song rate influences both the foray behaviour of a male’s social mate and the likelihood that he will sire extra-pair offspring with neighbouring females.     

Effects of early auditory experience on the development of local song preference in female swamp sparrows

A growing number of studies show that learning about male mating signals can shape the way females discriminate among males and may influence the evolution of both female preferences and the male traits under selection. Female songbirds commonly prefer local songs over foreign songs from a different population. In some species, however, the extent of variation among songs sung by different males within a population is as great as the variation observed between populations, raising the question of how females are able to discriminate local from foreign songs. Here, we report that laboratory-reared female swamp sparrows (Melospiza georgiana) not only show a preference for the particular song types with which they were tutored as compared with both foreign songs and unfamiliar local songs but also show preference for unfamiliar local songs over unfamiliar foreign songs. An acoustic analysis comparing tutor songs and those presented as unfamiliar local and foreign songs suggests that female swamp sparrows might be attuned to the specifics of local note phonology when assessing the attractiveness of unfamiliar songs. Our results demonstrate that early auditory experience influences response to geographic song variation in female swamp sparrows, and suggest the possibility that female songbirds may generalize what they learn from songs early in life to novel songs heard in adulthood. Additional work is needed to evaluate the contribution of unlearned predispositions for local song.     

Operant conditioning and copulation solicitation display assays reveal a stable preference for local song by female swamp sparrows <Emphasis Type="Italic">Melospiza georgiana</Emphasis>

Operant conditioning assays are increasingly being used to test mating signal preferences in female birds. Operant behavior may be seen as farther removed from mate choice behavior as compared to other methods for measuring mating signal preferences, which could limit the evolutionary interpretation of operant results. I compared the song preferences of female swamp sparrows (Melospiza georgiana) as measured both by a copulation solicitation display assay and by an operant preference test. Both methods revealed a strong preference for songs from the females' Conneaut Marsh breeding population over songs from a Millbrook population over 500 km distant, which remained stable after extensive exposure to Millbrook songs. Further, there was a striking congruence in results on an individual level from the two assays. These findings support the conclusion that operant methods reveal evolutionarily significant mate choice preferences, providing the opportunity to study such preferences under circumstances when the copulation solicitation assay is less practical.     

Song sharing in two populations of song sparrows (Melospiza melodia)

Sharing song types with immediate neighbors is widespread in birds with song repertoires, and sharing songs may confer a selective advantage in some cases. Levels of song sharing vary between different geographical populations of several bird species, and ecological differences often correlate with differences in singing behavior; in particular, males in migratory subspecies often share fewer songs than males in resident subspecies. The song sparrow (Melospiza melodia) appears to fit this pattern: resident song sparrows in western North America generally share 20–40% of their repertoire (of about eight songs) with each neighbor, while migratory subspecies from eastern North America often share 10% or less. We compared song sharing in two populations within a single subspecies of song sparrow (M. m. morphna) in Washington State. These populations, separated by only 120 km, nonetheless differ in migratory tendencies and several other ecological and life history variables. We recorded complete song repertoires from 11 male song sparrows in a high-elevation, migrating population at Gold Creek in west-central Washington, and compared them to two samples (n = 15 and n = 36) from a coastal, resident population at Discovery Park, Seattle, Washington. Despite major differences in habitat, population density, and migratory tendencies, song sharing among Gold Creek males was as high as that among Discovery Park males. In both populations, sharing was highest between immediate neighbors, and declined with distance. We conclude that at the within-subspecies level, neither migration nor population density affect song sharing in song sparrows, a song repertoire species. Received: 26 November 1998 / Received in revised form: 1 May 1999 / Accepted: 29 May 1999     

Female choice for complex song in the European starling: a field experiment

Male European starlings Sturnus vulgaris sing long complex songs that appear to be important in the courtship of females but which also influence competitive interactions between males. We tested the hypothesis that females choose mates on the basis of the complexity of their songs, rather than on the quality of the territories the males defended. In order to determine whether certain territories were preferred over others, the first set of birds to settle in the experimental nest-boxes was removed and a second set allowed to settle. Consistent preferences for certain nest-boxes were indicated by correlations between the settlement patterns of the first and second sets of birds. However, males with the most complex song did not necessarily occupy the most preferred nest sites. Males with more complex song acquired mates faster. This relationship remained significant when nest-site preference was statistically controlled, indicating that female starlings chose males with complex song rather than those that defended preferred nest sites. A number of morphological variables were also found to be uncorrelated with female choice. Song complexity in European starlings increases with age, and the evolution of song complexity in this species is consistent with an age-indicator model of sexual selection. Males with larger repertoires were also in better condition, indicating that females obtain high-quality mates by choosing on the basis of male song. Received: 29 April 1995/Accepted after revision: 9 September 1995     

Developmental stress affects the attractiveness of male song and female choice in the zebra finch (Taeniopygia guttata)

Developmental stress has recently been shown to have adverse effects upon adult male song structure in birds, which may well act as an honest signal of male quality to discriminating females. However, it still remains to be shown if females can discriminate between the songs of stressed and non-stressed males. Here we use a novel experimental design using an active choice paradigm to investigate preferences in captive female zebra finches (Taeniopygia guttata). Nine females were exposed to ten pairs of songs by previously stressed and non-stressed birds that had learned their song from the same tutor. Song pairs differed significantly in terms of song complexity, with songs of stressed males exhibiting lower numbers of syllables and fewer different syllables in a phrase. Song rate and peak frequency did not differ between stressed and non-stressed males. Females showed a significant preference for non-stressed songs in terms of directed perching activity and time spent on perches. Our results therefore indicate that developmental stress affects not only the structure of male song, but that such structural differences are biologically relevant to female mate choice decisions.     

Changes in singing behavior of male black-capped chickadees (Parus atricapillus) following mate removal

We removed the mates of ten male black-capped chickadees (Pares atricapillus) during the nest-building period to determine the effect of female presence on dawn singing. During the first dawn chorus following mate removal, males sang significantly longer, increased movement within their territory, and increased the percentage of their territory covered while singing. After the female was returned, these parameters returned to the pre-removal values. Males did not alter the frequency range or modal frequency of their songs when the mate was removed, nor did they change the degree of frequency shifting in the fee-bee song. We conclude that dawn singing in the black-capped chickadee acts, in part, as an intersexual signal, and that the behavior of frequency shifting in the song may be directed more toward rival males than females. Correspondence to: K. Otter     

Badge size in the house sparrow Passer domesticus

Summary I studied female mate choice in house sparrows Passer domesticus in relation to the size of the black throat patch of males (badge size), which is a signal of dominance status, and to territory quality. Males with large badges obtained a mate earlier in spring than males with small badges. Males which remained unmated during the entire breeding season had smaller badges than mated males, even when controlling for the effect of other morphological traits and age. Largebadged males had territories with more breeding sites than small-badged males. Territories defended by males with large badges primarily had hole nest sites, which were safe from predators, and nestlings rarely fell from hole nests. Females were implanted with estradiol to induce copulation solicitation displays. Females responded more strongly to a male taxidermic mount and song than to song alone, and they responded more strongly and frequently to male mounts with large badges. Female house sparrows chose mates on the basis of male badges and perhaps on the basis of the quality of the nesting territories offered.     

Mate choice plasticity in the field cricket <Emphasis Type="Italic">Teleogryllus oceanicus</Emphasis>: effects of social experience in multiple modalities

Social experience can elicit phenotypically plastic changes in mate choice, but little is known about the degree to which social information from one modality can influence mating decisions based on information from a different modality. I used the field cricket Teleogryllus oceanicus to test whether experience of chemical cues mimicking a high density of sexually mature males causes changes in mate choice based on acoustic signals. T. oceanicus males produce long-range calling songs to attract females for mating, but they also produce waxy, non-volatile hydrocarbons on their cuticle (CHCs) which, when deposited on a substrate, can be detected by females and may provide demographic information. I manipulated female experience of substrate-bound male CHCs and then performed acoustic mate choice trials. When CHCs were present on the substrate during trials, females showed greater motivation to respond to male calling song. This effect diminished with repeated exposure to male songs, demonstrating that the importance of olfactory cues in altering acoustic mate choice decreased with increasing exposure to acoustic signals. However, the temporal nature of CHC experience mattered: previous experience of CHCs did not alter subsequent female choice for male calling song traits. Exposure to male song increased the threshold of mate acceptance over time, and individuals varied considerably in overall levels of responsiveness. Taken together, the results demonstrate that mate choice is dependent on social context mediated by multiple modalities in T. oceanicus, but they do not support the idea that prior experience of social cues in one modality necessarily influences later mating decisions based on other signalling modalities.     

Song length variation serves multiple functions in the white-crowned sparrow

A wide variety of hypotheses has been proposed to explain the structural diversity in bird song repertoires. Song diversity is frequently described in terms of song “types” or within-type “variants.” Male Puget Sound white-crowned sparrows, Zonotrichia leucophrys pugetensis, produce variants of their single adult song type by altering the number of repetitions of syllables in the terminal trill. We tested whether variation in trill length correlated with distance to the receiver and with signaling context as predicted by the eavesdropping avoidance hypothesis and the strategic signaling hypothesis. In accordance with the eavesdropping avoidance hypothesis, males sang variants with shorter trills, and sang quieter and less frequently when near their mate during the incubation phase than during spontaneous singing while unpaired. Males also sang variants with short trills, but at a high rate and variable amplitude when within 10 m of an opponent during close male–male territorial interactions. In agreement with the strategic signaling hypothesis, males decreased trill length immediately before chasing an opponent, but did not change length consistently prior to flight. We conclude that the occurrence of short quiet songs sung near the mate agrees with predictions of the eavesdropping avoidance hypothesis, while short songs sung near other males are best explained by the strategic signaling hypothesis. Trill length variation may be a conventional signal of aggressive intentions in male–male contests stabilized by receiver-imposed retaliation costs.     

Use of trace element analysis of feathers as a tool to track fine-scale dispersal in birds

Tracking dispersal and migratory movements of animals over small and large spatial scales is a challenge. In birds, a promising yet underutilized tool is the trace elemental composition of feathers. The elemental profile of a feather may reveal information about the geographic origin of a bird provided that molting occurs on the breeding grounds and that elemental differences exist between breeding areas. Here, we explore the use of trace elemental composition in body feathers of the Puget Sound white-crowned sparrow Zonotrichia leucophrys pugetensis as a tool (1) to discriminate among birds collected in four different song dialect populations along a 400-km stretch of the Pacific Northwest coast and (2) to assign males singing nonlocal dialects in one population to potential natal populations. Inductively coupled plasma mass spectrometry detected 34 trace elements in sampled feathers and in a discriminant function analysis seven of these elements differed among the four source populations. Half of the six nonlocal dialect singers, who were likely to have immigrated into the focal population, were assigned to a population that matched their song dialect. Our study suggests that feather microchemistry is a promising tool for identifying geographic origins of dispersing birds over small geographic scales and in combination with other markers, such as song, may give insight into ecological and evolutionary processes.     

Song output and stimulation of the female in white-throated sparrows

Summary We investigated the importance of song length and singing rate in stimulating female white-throated sparrows, Zonotrichia albicollis. In November 1988 ten female and one male white-throated sparrow were captured during the fall migration. To enhance the expression of sexual receptivity, the females were implanted with 17-beta-estradiol silastic pellets. Using the visual stimulus of a non-singing male to further enhance the expression of sexual receptivity in the females, we found that females gave a greater response, in the form of copulation displays, to a five-note versus a two-note version of a typical male white-throated sparrow song. Each version was played back at four songs per minute. In May 1990 birds were captured and treated as before, except that the two-note song was played at ten songs per minute and the five-note song at four songs per minute. Therefore, each female heard twenty notes per minute. In the second experiment, the females did not show a statistical difference in response to the two- and five-note song playbacks. We interpret the results of the second experiment as indicating the song rate as well as song length is important in stimulating female white-throated sparrows because increasing the rate of the two-note song brought the response up to the level of response we obtained to the five-note song played at the slower rate. We conclude that in white-throated sparrows, song output is important for female stimulation.     

Song of the humpback whale — Population comparisons

Summary Humpback whale songs recorded on tropical calving grounds exhibit different dialects depending on the oceanic basin. Songs sampled simultaneously from two populations in the North Pacific (Hawaii and Mexico) were essentially identical. These North Pacific songs were clearly different from the song type shared by two populations in the North Atlantic (Cape Verde Islands and West Indies). Songs from the Southern Hemisphere (Tonga) represent a third distinct dialect. Our evidence shows that, despite annual change in song organization, significant differences in humpback song occur between isolated ocean basins, while only subtle differences exist within an oceanic population (Hawaii and Pacific Mexico).     

Trade-off between mate guarding and mate attraction in the polygynous great reed warbler

Summary In a Swedish population of the polygynous great reed warbler Acrocephalus arundinaceus, about 40% of the males formed pairs with more than one female. Males sang two completely separated types of song: (1) long song when they tried to attract mates and (2) short shong when they guarded a fertile female. As soon as a male had attracted a female he immediately switched from long to short song and apparently guarded her for at least 3 days. Most males left their female and started singing long several days before her fertile period ended. This behavior probably increased the risk of cuckoldry. By assuming that males of polygynous species maximize their fitness over the whole breeding season (i.e., maximize fitness rate), we predicted longer mate guarding periods when the probability of attracting a second female was low and the risk of cuckoldry was high. These predictions were supported by observations. The probability of attracting a second female decreased during the breeding season and, in accordance, the number of days that males sang long song during the primary female's fertile period was negatively correlated with the time of the season. This trend held also for individual males when comparing mating periods of their primary and secondary female. The increasing rate of male intrusions with season may also have contributed to the increasing mate guarding periods. Offprint requests to: D. Hasselquist     

Song-type sharing in song sparrows: implications for repertoire function and song learning

One hypothesis for the function of song repertoires is that males learn multiple song types so that they may share songs with neighbors, allowing them to match during territorial interactions. In at least one song sparrow population, in Washington, territorial males share a high proportion of song types with their neighbors and use these shared songs in matching. We recorded song sparrows in Pennsylvania and quantified sharing of whole songs and song segments. We found that song sharing is an order of magnitude less common in the Pennsylvania population. We found sharing of song segments to be significantly more common than the sharing of whole songs in three of the five fields we examined, while we found no significant differences between whole and partial song sharing in the remaining two fields. Finally, we found no evidence that sharing is greater between birds in the same field compared to birds in different fields. Taken with the data from Washington song sparrows, these results provide evidence for intraspecific geographic variation in the organization of song repertoires, and suggest that song sharing has not been a strong selective force in the evolution of song repertoires in song sparrows as a species. Furthermore, Washington and Pennsylvania song sparrows differ in how they learn song, in that Washington birds copy whole songs, while Pennsylvania birds appear to copy and recombine song segments, as has been found in laboratory studies of song learning. Thus both song learning and the function of song repertoires differ between populations of song sparrows. Such intraspecific geographic variation offers a unique opportunity to explore the ecological and historical factors which have influenced the evolution of song. Received: 30 June 1997 / Accepted after revision: 8 March 1998