Michel Kreutzer

Female canaries are sexually responsive to special song phrases

The sexual responsiveness of female canaries, Serinus canaria, to six different types of male song phrases extracted from natural song was tested. Copulation solicitation displays were used as an index of female sexual response. Playbacks were performed several days before and during egg laying (a period of natural sexual responsiveness of the females to song). Female canaries were especially responsive to particular short phrases whose essential features were abrupt frequency fall and short silences. This differential responsiveness occurred whatever the serial position (beginning, middle or end) of the phrase in the song and its serial relationship to other different conspecific phrases as well as the general song context (conspecific or heterospecific phrases). Influences such as early experience or ‘sensory bias’ that may lead to a particular sexual sensitivity of female canaries to these types of song phrases are discussed.

Directional female preference for an exaggerated male trait in canary (Serinus canaria) song.

Motor constraints on vocal production impose a trade–off between trill rate and frequency bandwidth within birdsong. We tested whether domesticated canary (Serinus canaria) females, reared either in acoustic isolation or in aviary conditions, had a preference for broad bandwidth songs with artificially increased syllable rates. The copulation solicitation display (CSD) was used as an index of female preference. As predicted, both naive and experienced females were especially responsive to syllables with a broad bandwidth emitted at an artificially increased rate. Female preference for supernormal stimuli provide support for the honest–signalling hypothesis and our results are consistent with recent findings indicating that production of song phrases maximizing both bandwidth and syllable rate may be a reliable indicator of male physical or behavioural qualities. We suggest that female preference for vocal emissions, which simultaneously maximize these two parameters, could be a widespread pattern within songbirds.

Female canaries produce eggs with greater amounts of testosterone when exposed to preferred male song

Male birdsong has a great influence in the stimulation of female reproduction. However, female physiological responsiveness to song may depend on the degree of complexity of male song. This is expected because females of iteroparous organisms may increase their fitness by matching their reproductive investment to the predicted value of each reproductive attempt. To the extent that the expression of male ornaments is a signal of male quality, we expect females to increase their investment when paired to highly ornamented males. However, female investment may be cryptic and difficult to detect, such as androgen content in the eggs. In this study, we exposed female canaries (Serinus canaria) to attractive and unattractive song repertoires using a crossover design. As predicted, females invested greater concentrations of testosterone in their eggs when exposed to attractive repertoires than when exposed to unattractive repertoires. This implies that song repertoires convey important information about the reproductive value of a given male and suggests that testosterone deposition in egg yolk may be costly.

The selectivity of sexual responses to song displays: effects of partial chemical lesion of the HVC in female canaries

By stimulating female canaries with computer edited songs, we investigated the involvement of the caudal nucleus of the ventral hyperstriatum or high vocal center (HVC) in the selectivity of sexual responsiveness to different kinds of conspecific songs. Due to the fact that the types of conspecific song phrases act as relevant cues to give song its sexual potency, we compared courtship responses to two conspecific songs, highly sexually-stimulating and weakly sexually-stimulating song, before and after the partial ibotenate lesion of the HVC. Sexual responses to heterospecific song were also tested. Copulation solicitation displays were used as an index of female responses. The partial chemical lesions of the HVC whatever the HVC portion damaged affected female bird behavior; they responded more strongly to weakly sexually-stimulating song and to heterospecific song than before the lesions. However, the conspecific sexually attractive song continued to elicit the highest level of sexual displays. None of the control birds ever altered their pattern of responses to the three song types. The results suggest that the HVC is part of the neural network engaged in the control of sexual preferences to conspecific song displays.

In a songbird, the black redstart, parents use acoustic cues to discriminate between their different fledglings

Several studies on parental investment in territorial songbirds have reported the existence of brood division. This is a type of postfledging care in which each parent has long-term feeding preferences for different young within a brood, creating two family units. Recent theoretical work indicates that conflicts between individuals should select for brood division. However, little is known about the mechanisms involved in the onset and maintenance of this behavioural strategy. Given the high rate of fledglings’ begging calls, we hypothesized that acoustic discrimination could explain the stability of feeding preferences at a proximate level. In a 3-year field study, we recorded the responses of parent black redstarts, Phoenicurus ochruros, a territorial songbird, to playback of the begging calls of fledglings fed by the male and by the female. Parents responded more to the calls of the fledglings that they preferentially fed. A principal component analysis of the calls suggested that parents may recognize individual offspring. To our knowledge, this study provides the first evidence that a bird can acoustically discriminate between two categories of its own offspring: those that it preferentially feeds and those fed by the other parent.

Obtaining copulation solicitation displays in female canaries without estradiol implants

Female domesticated canaries (Serinus canaria) respond to conspecific song with copulation solicitation display (CSD) between 22 and 27 days after their first offspring has hatched. This period could be used to investigate the acoustical preferences of female canaries. This non-invasive method respects the natural reproductive cycle and could be an alternative to the invasive method of estradiol implants.

Effects of fadrozole on sexual displays and reproductive activity in the female canary

We used fadrozole, a potent inhibitor of the aromatization of androgens to estrogens, to investigate the influence of estradiol on copulation solicitation displays (CSD) and reproductive activity in female canaries (Serinus canaria). Systemic injections of fadrozole during 10 consecutive days were effective in reducing plasma estradiol concentrations in adult female canaries submitted to photostimulation. Fadrozole provides a powerful tool for limiting an individuals exposure to estradiol, and the results of this study emphasize the influence of estradiol secretion in the regulation of behavioral transitions along the reproductive cycle of the female canary. When females were injected at the beginning of photostimulation, the emergence of copulation solicitation displays in response to conspecific songs was delayed. When females were injected later, after they were sexually active, the fadrozole treatment did not affect sexual displays. These results are consistent with the hypothesis that a threshold level of estradiol is critical to activate the neural circuitry mediating the copulation solicitation displays response in the female canary. They also suggest that the magnitude of sexual response is not related in a dose-dependent manner to estrogen concentrations observed during the period of sexual responsiveness. When females were injected at the beginning of photostimulation, egg-laying was delayed; when females were injected later, after they were sexually active, the fadrozole treatment dramatically reduced egg-laying and prevented incubation.

Parental care and brood division in a songbird, the black redstart

Sexual conflict over parental care can be mediated through differences in male and female overall feeding rates, brood division or both. At present, it is not clear whether post-fledging brood division occurs due to sexual conflict over parental investment or is due to bi-parental cooperation, e.g. increase offspring fitness. We provide evidence suggesting that brood division in the black redstart, Phoenicurus ochruros is due to sexual conflict. Males and females had similar feeding contributions during the nestling stage, which is common for most passerine species. After fledging, each parent showed long-term feeding preferences for particular chicks within the brood. In most cases (74%; 17/23) both parents provided care but males tended to feed less fledglings than females did and in about a quarter of cases (26%; 6/23) females fed the whole brood by themselves. The relative amount of male to female post-fledging feedings showed a significant negative relationship with the proportion of fledglings cared for exclusively by the male. These results suggest (1) a close link between the amount of parental care and brood division; (2) sexual conflict can be mediated through brood division; (3) female redstarts appear to loose this conflict more often than male redstarts, with in the extreme cases males showing post-fledging brood desertion. A literature review shows brood division to occur in at least a dozen of songbird species but male black redstarts have the lowest relative post-fledging parental investment, expressed either as feeding rates or number of chicks in care.

Early tutoring and adult reproductive behaviour in female domestic canary (Serinus canaria)

Abstract We studied the effect of early tutoring on the subsequent sexual preferences and reproductive activity of female domestic canaries (Serinus canaria). Young female canaries were exposed during the first 4 months of life to songs of either domestic or wild canaries. When adult, these females were again exposed to domestic or wild songs. In the first experiment, the sexual responses of the females to unfamiliar domestic and wild songs were quantified with the copulation solicitation display (CSD) assay. In the second experiment, the same females were tested again with modified tutoring songs. In the third experiment, song stimulation of nest-building and egg-laying was studied. Domestic-strain-tutored females gave more CSDs to domestic than to wild songs. In contrast, wild-strain-tutored females showed no sexual preference. We propose that the sexual preference of adult domestic-strain-tutored female canaries for domestic songs is the consequence of learning and categorisation processes. The discrepancy between the results of the domestic-strain-tutored females and those of the wild-strain-tutored females suggests that female canaries have a predisposition to learn songs of their own strain rather than songs of an alien strain. In the third experiment nest-building and egg-laying activities appeared to be unaffected by early tutoring conditions: there was no significant differential effect of the different tutoring and exposure conditions on nest-building and egg-laying scores. Mate attraction and stimulation of females’ reproductive activity appear to be two separate functions of male song, which may have been shaped by different evolutionary constraints.

Social stimulation modulates the use of the 'A' phrase in male canary songs

The songs of male canaries are composed of different phrases; a phrase is defined as a segment of song composed by the repetition of the same syllable. When singing alone or in the presence of a male or female conspecific, the number and duration of the songs of male domestic canaries are similar. Despite these similarities, there are differences in the production of phrases between confrontations with conspecifics and singing alone. The presence of another canary, either male or female, induced songs which were characterized by longer strings of A phrases. We have previously demonstrated that this particular phrase elicited many more copulation sollicitation displays in female canaries than other kinds of phrases in the canary repertoire. Thus, the phrase A may be used by the singing males so as to affirm their readiness to interact. By singing A phrases male canaries may communicate both intrasexually (e.g. challenge to male competitors) and intersexually (e.g. courtship of the female). Thus two functions can be linked together in the same signal, the male or female receiver either having different perceptions or giving different senses to the same vocalization.