Vocal mimicry of the paraside whydahs (Vidua) and response of female whydahs to the songs of their hosts (Pytilia) and their mimics

Parasitic paradise whydahs (Vidua paradisaea) mimic the vocalizations of their hosts, Pytilia melba. Photostimulated female whydahs isolated in large aviaries responded to broadcasts of recorded song. Approach occurred significantly more often to songs of the host species P. melba than to the similar P. phoenicoptera. Females approached with equal frequency the songs recorded from their hosts and the mimetic songs of the male whydahs. No significant differences were found between the responses of females to songs of sympatric and allopatric forms of their host. It is suggested that mimetic songs of males and the responses of females are behavioural isolating mechanisms among species of whydahs.     

The behavioural basis of overdominance in competitive mating success at the ebony locus of Drosophila melanogaster

Male files homozygous for the gene ebony¹¹ are partially blind, and at a disadvantage in competitive mating. The courtship of the mutant males is deficient in wing vibration stimulation, which is characterized by a low proportion of sine song and a high intra-pulse frequency. Males heterozygous for ebony have normal vision, but show an increase in courtship song, and are superior in competitive mating to wild type males. The auditory characteristics of courtship song produced by heterozygous males are indistinguishable from those of wild type, and their superiority in competitive mating success is due to overdominance involving this specific element of male courtship behaviour.     

Effects of long-acting testosterone treatment on freeliving pied flycatchers, Ficedula hypoleuca, during the breeding period

Breeding behaviour and spermatogenesis of all males in a population of pied flycatchers, Ficedula hypoleuca, were experimentally prolonged by long-acting testosterone. The behaviour of these birds was compared with that of birds from an untreated population and a population where the males were given the vehicle only. The testosterone treatment prolonged territorial behaviour, and a higher percentage of nests without a feeding male during the nestling period was found in the experimental area. The proportion of polygamous males did not however differ between the experimental and control areas. The feeding activity of those testosterone-treated males returning to their home territories was markedly depressed. The female of such a pair did not compensate for the male's low feeding activity, but fed the nestlings as she would have done with a normal untreated male at the nest. On the other hand, females without a male present during the nestling period compensated for their mates' absence by increasing their own feeding frequency. It was also shown that the song of the male pied flycatcher is dependent upon androgens. The testosterone-treated males produced fewer fledglings than the control males.     

Female proximity stimulates development of male competition in juvenile brown-headed cowbirds, Molothrus ater

We investigated how individual variation in social behaviour among group members interacts to affect social structure and development of reproductive skills. We randomly assigned juvenile male and juvenile and adult female cowbirds to four aviaries and observed patterns of singing and social assortment in each. Although social composition of each aviary was the same, juvenile males in one aviary engaged in more intra- and intersexual affiliation and singing interactions. We designed a series of rotations of individuals among the aviaries to determine which individual traits were responsible for the observed group differences. First, we rotated groups of three males from a less interactive aviary into a more interactive aviary, replacing interactive males. Within 4 days, the rotated males changed their behaviour to match the aviary into which they had been moved (i.e. interactive males became less interactive and vice versa). Next, we rotated juvenile females through the aviaries. After this rotation, the behaviour of the juvenile females remained the same, but the behaviour of the resident males changed, becoming like the males in the females' former aviaries (i.e. when juvenile females were moved from an interactive aviary into a noninteractive aviary, the males in the new aviary became more interactive and vice versa). Across the aviaries, the amount of female-male associations correlated positively with male-male competition. During the breeding season, males that had experienced more competition over the year received more copulations than males that had experienced little competition. Furthermore, more eggs were produced in aviaries containing competitive males than in aviaries containing less competitive males. Past work has shown that females can influence male vocal development; here we show that they can also influence male social development. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Female response song in the ephippigerines Steropleurus stali and Platystolus obvius (Orthoptera,Tettigoniidae)

Stridulation by females of Steropleurus stali and Platystolus obvius in response to the calling song of the males was observed and recorded. The response has only been stimulated by the appropriate male song, either directly or from a recording. The structure of the files and the form of stridulation in both sexes is described. The male song of S. stali is remarkable in that only a few teeth on the file are struck in each wing movement. It is also notable that both opening and closing wing strokes contribute more or less equally to the syllable. The female song is similar but distinct. The song of P. obvius male is a single chirp involving nearly all the teeth on the file and with the main emphasis on the closing syllable. The response song of the female is a very brief chirp. These species are only sporadic singers, but when the female responds they are stimulated into greater activity. They thus contrast with reiterative singers like Ephippiger in which there is no female response. The implications of these contrasting behavioural patterns is 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.     

Intraspecific acoustical interference in the white-throated sparrow (Zonotrichia albicollis)

Intraspecific acoustical interference was studied in the white-throated sparrow (Zonolrichia albicollis). It was found that individuals avoid singing during a song of a conspecific. The effect is significantly greater with neighbours that are closer to them. The evolutionary implications of this phenomenon for the properties of song in Z. albicollis are discussed.     

Imprinting and the origin of parasite-host species associations in brood-parasitic indigobirds, Vidua chalybeata

Brood-parasitic village indigobirds, Vidua chalybeata, were bred in captivity and foster-reared by their normal host species, the red-billed firefinch, Lagonosticta senegala, or by an experimental foster species, the Bengalese finch, Lonchura striata. Captive-reared female indigobirds were tested as adults for mate choice and for host choice. In tests of mate choice, female indigobirds responded preferentially towards mimicry songs of male indigobirds that were similar to those of the females' own foster parents. Females reared by Bengalese finches responded to male songs that mimicked Bengalese finch song rather than to male songs that mimicked their normal host species, the firefinch. In tests of host choice, females reared by Bengalese finches laid in the nests of Bengalese finches, and females reared by firefinches laid in the nests of firefinches. Wild-caught females showed the same behaviours as captive-bred females reared by firefinches. A female indigobird's social companions (firefinch or Bengalese) following her independence of her foster parents had no effect on her sexual response to male mimicry song or her choice of a host species in brood parasitism. The results support the predictions of a model of imprinting-like behaviour development in which young indigobirds focus their attention on their foster parents, rather than a model of innate bias for songs and nests of their normal host species, or a null model of nonspecific brood parasitism and differential survival. The results provide experimental support for the recent origin of brood parasite-host associations and the significance of imprinting in speciation in these brood parasites. Copyright 2000 The Association for the Study of Animal Behaviour.     

Acoustic preference functions and sexual selection on the male calling song in the grasshopper Chorthippus biguttulus

Male courtship songs have two functions in species recognition and intraspecific mate choice. Female preference might thus exert different types of selection pressure on male song traits. We used a combination of acoustic mate choice experiments and statistical analyses to examine how traits of the calling songs of male nightingale grasshoppers,Chorthippus biguttulus , are influenced by different sexual selection pressures. We recorded calling songs of males and tested their attractiveness to females in acoustic mate choice experiments. The attractiveness values were a good estimate of the potential male mating success. In experiments with a pair of males, females copulated significantly more often with the male that had the higher attractiveness value. To detect directional, stabilizing, disruptive or correlative selection acting on male song properties we used linear and nonlinear regressions between male song traits and female response behaviour. Three signal traits were revealed to be under directional selection: song loudness, pause to syllable ratio and the mean duration of gaps within syllables. A nonlinear regression testing for correlative selection showed that a fourth song trait, rhythm, in combination with mean gap duration was also important for female mate choice. With these traits and trait combinations we were able to explain 42% of the variance in attractiveness between males. Since we found no evidence for stabilizing selection, but ample evidence for directional selection, we conclude that selection on the traits examined is related to mate choice mainly in the context of intraspecific sexual selection and probably less so in species recognition. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Latent song type memories are accessible through auditory stimulation in a hand-reared songbird

The production of learned vocalizations such as in birdsong is often used to judge whether stimuli had been memorized upon their presentation. However, failures in the imitation of certain song patterns may also reflect impaired development of motor programmes or impaired memory retrieval rather than failures in stimulus memorization during auditory acquisition. To study this issue, we confronted adult hand-reared nightingales, Luscinia megarhynchos, with interactive playback experiments and used vocal matching as a behavioural tool to investigate their song type memories. Vocal matching is a common pattern-specific response that songbirds use in territorial countersinging. We distinguished two forms of pattern-specific matching: (1) song type matching (i.e. a bird replied with the same song type as the stimulus song), and (2) song group matching (i.e. the bird replied with a different song type which was, however, sequentially associated with the playback song presented earlier, i.e. during the tutoring). Some subjects used both song type and song group matching in response to song types they had not imitated from the tutor programme prior to the playback experiments. Our results indicate that nightingales store more song types in their sensory phase than they spontaneously recall from memory as adults. That is, memories of song types that were not performed in overt behaviour could be activated by vocal interactions, here induced by the interactive playback. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Species and sex-specific songs and courtship behaviour in the genus Zaprionus (Diptera-Drosophilidae)

Courtship behaviour and songs of six Zaprionus species show differences not only between species but also between sexes. Courtship behaviour differs from that in the related genus Drosophila. In most species, males produce two song types which may alternate or be repeated. Singing occurs during courtship displays, mounting, after copulation and briefly during male-to-male interactions. Females produce a loud whine and body rocking movements in refusal but have a species-specific pulsed song produced during normal courtship which differs from the conspecific male song. One species produces an irregular male song but a regular female song. Sex-specific songs may have selective advantages but pose problems for the sensory template hypothesis.     

The role of auditory stimuli in the courtship of Drosophila melanogaster

Simulated courtship song of male Drosophila melanogaster was played to males or females of this species. Upon receiving the song males increase their locomotor activity and start courting each other, whereas females reduce their locomotor activity. In wingless males the locomotor activity difference between the silent control and the experimental sound situation is much larger than in winged males, due to the inactivity of wingless males in the control situation. Males which had been kept singly up to the time of the experiment exhibit higher locomotor and sexual activity than group housed males. A second component of the male courtship song ‘sine song’ is described, together with experiments which investigate the sensory basis of the effect male courtship song has on males.     

Reproductive activity and physiological status of the calanoid copepods Calanus helgolandicus and Calanoides carinatus under food-limiting conditions

The reproductive activity and the physiological state of the calanoid copepods Calanus helgolandicus and Calanoides carinatus were investigated off the coast of NW Spain during autumn to evaluate the effect of short food resources on both populations. Phytoplankton biomass was low, and neither phytoplankton size distribution nor composition was suitable to support high reproductive rates. Accordingly, egg production rates (EPR) were much lower than maximum rates for both species, pointing to food limitation. The reproductive index (RI), which represents the proportion of females with mature gonads, was < 50% at each of the three zones into which the sampling area was divided (coast, shelf and ocean). Potential recruitment rates were very low except at some nearshore stations, where the highest concentrations of chlorophyll-a (Chl-a), diatoms, dinoflagellates and large cells were found. EPR of C. helgolandicus and C. carinatus were correlated with phytoplankton biomass and unaffected by temperature. Phytoplankton carbon ingestion explained ca. 50% of the variability in EPR for both species. At most of the stations, herbivory was insufficient to cover the carbon requirements for reproduction and respiration, so females probably fed on heterotrophic prey to meet their demands. However, given the low fecundity observed, this omnivorous diet did not seem to be optimum for reproduction, and a severe food limitation is thus suggested. Furthermore, the high C/N values measured point to a notable lipid storage, but given the low EPR found, lipid reserves were probably invested into female maintenance rather than into gonad maturation. C. helgolandicus and C. carinatus populations did not mirror phytoplankton biomass distribution, but they correlated well when considering only copepodites V (CV). The CV could be preparing for the overwintering, storing lipid reserves to ensure a successful diapause, and they could also be advected by the poleward current detected during the study. Females showed a diel feeding rhythm, with highest ingestion rates during night. From our results, it follows that C. helgolandicus and C. carinatus females did not perform diel vertical migrations. We suggest that this behaviour is likely due to the food-limiting conditions, which make it more advantageous to remain at the surface during daytime.     

Courtship songs and genetic control of their acoustic characteristics in sibling species of the Drosophila melanogaster subgroup

Six sibling species of the melanogaster subgroup differ in their wing displays and in the acoustic characteristics of their courtship songs. D. melanogaster, D. simulans and D. mauritiana have distinct but similar courtship songs. D. mauritiana, which is allopatric to the others, produces, an ambivalent song with sine song frequency and intrapulse frequency like simulans and modal interpulse interval like melanogaster. These three species appear to be behaviourally more closely similar to each other than to the three African species D. yakuba, D. teissieri and D. erecta. The acoustic characteristics of the songs of interspecific hybrids, indicate that the interpulse interval and intrapulse frequency are quantitatively controlled by genes located on the autosomes. The ability to generate sine song may be controlled by one or more genes located on the X-chromosome, but an alternative possibility, of autosomal dominant inheritance, cannot be excluded.     

The function of pulse song and sine song in the courtship of Drosophila melanogaster

Drosophila melanogaster females were subjected to pulse song before being allowed to mix with males. Sine song increases female receptivity, pulse song does not. Pulse song does however increase receptivity if the females are subjected to it while being courted by males which are deaf and which cannot produce any auditory stimulation themselves. It is suggested that sine song is summated and has a priming effect on female receptivity whereas pulse song functions as a species recognition signal in a trigger-like fashion.     

Behavioural insensitivity to supplementary testosterone during the parental phase in the chestnut-collared longspur,Calcarius ornatus

In seasonally breeding male birds that show paternal care, plasma testosterone (T) peaks in the early spring coincident with territory establishment and pair bonding. Once nests are initiated, T declines precipitously and remains low as nestlings hatch and males become parental. A growing body of evidence suggests there is a trade-off between a male's level of T and his expression of paternal care: high T enhances sexual behaviour but reduces paternal care. Male chestnut-collared longspurs show high levels of paternal care. They feed and brood young, act as nest sentries and aggressively defend the nest against predators. We experimentally altered males' plasma levels of T such that the early spring T peak was extended through the parental phase. T enhanced song behaviour typical of the sexual phase and decreased nest sentry behaviour during incubation, but did not reduce brooding or feeding of nestlings. Thus, males responded behaviourally to T during incubation, but, unlike most other temperate-breeding birds studied, did not respond to T after eggs hatched. Based on these data and similar results in an Arctic passerine, we suggest that the pattern of males' reduced responsiveness to T during the nestling phase may reflect the relative importance of male care to nest success in this species, or a phylogenetic constraint common to the genusCalcarius . Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

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.     

Defensive behaviour and its inheritance in the anabantoid fish, Macropodus opercularis and Macropodus opercularis concolor

In this preliminary study defense behaviour patterns (fear responses) are described in two closely related, behaviourally different inbred labyrinth fish subspecies and in their F₁ generation. The subspecies M. opercularis (characterized briefly by “active escape”) and M. opercularis concolor (characterized by “passive escape”) showed specific differences in the manifestation of certain defense behaviour patterns. In the F₁ hybrid generation dominance and overdominance of M. opercularis was found in most defense behaviour patterns. Analysing the frequencies and sequences of movement patterns it could be shown that defensive behaviour is not a random or entirely “plastic” process but that there is sequential linkage between the patterns and they form characteristic clusters. Our results suggest that manifestations of different patterns are under genetic control and presumably, genetic determination of certain patterns is not very complex. Attempts were made to determine whole brain noradrenaline, serotonine and dopamine levels of the two subspecies and a significant difference was found in the noradrenaline content.     

The function of courtship song rhythms in Drosophila

The courtship songs of Drosophila are produced by the male's wing vibration and consist of a series of pulses, with an inter-pulse interval (IPI) of 34 ms for D. melanogaster and 48 ms for D. simulans. The IPI's are not constant in length during courtship, but oscillate sinusoidally with 55-s cycles in the former species and 35-s cycles in the latter. We have stimulated D. melanogaster females with artificially generated courtship songs, and have observed that they mate fastest when the song incorporates a 55-s oscillation superimposed on a 34-ms IPI. D. simulans females, on the other hand, mate fastest with a 48-ms IPI and a 35-s oscillation period. Consequently these newly-discovered song cycles produce significant mating enhancement in these species, with the females showing a preference for songs which carry both the species-specific IPI and the species-specific IPI rhythm.     

Captive Rearing Experiments Confirm Song Development without Learning in a Tracheophone Suboscine Bird

The origin of vocal learning in animals has long been the subject of debate, but progress has been limited by uncertainty regarding the distribution of learning mechanisms across the tree of life, even for model systems such as birdsong. In particular, the importance of learning is well known in oscine songbirds, but disputed in suboscines. Members of this diverse group (∼1150 species) are generally assumed not to learn their songs, but empirical evidence is scarce, with previous studies restricted to the bronchophone (non-tracheophone) clade. Here, we conduct the first experimental study of song development in a tracheophone suboscine bird by rearing spotted antbird (Hylophylax naevioides) chicks in soundproofed aviaries. Individuals were raised either in silence with no tutor or exposed to standardized playback of a heterospecific tutor. All individuals surviving to maturity took a minimum of 79 days to produce a crystallized version of adult song, which in all cases was indistinguishable from wild song types of their own species. These first insights into song development in tracheophone suboscines suggest that adult songs are innate rather than learnt. Given that empirical evidence for song learning in suboscines is restricted to polygamous and lek-mating species, whereas tracheophone suboscines are mainly monogamous with long-term social bonds, our results are consistent with the view that sexual selection promotes song learning in birds.