Effects of Song Experience and Song Quality on Immediate Early Gene Expression in Female Canaries (Serinus canaria)

Female songbirds are thought to make mate choices based on aspects of male song quality. Male canaries (Serinus canaria) produce songs with “special” syllables that have been shown to be highly salient to female listeners – eliciting high rates of sexual displays and enhanced immediate early gene (IEG) expression. Immunohistochemistry for the IEG ZENK was used to examine the effects of experience with these syllables on activity in the caudal mesopallium (CMM) and nidocaudal mesopallium (NCM), two auditory areas important in processing conspecific song. Photostimulated female canaries were housed in sound attenuated chambers and played pseudosongs containing either three special syllables or three non‐special syllables, an intro, and an outro sequence. Females that heard special syllable pseudosongs exhibited higher ZENK expression in CMM. To assess the effects of experience, photostimulated females were pair housed and exposed to playback of song with or without special syllables for 14 days. After transfer to individual housing, birds were played one of the aforementioned stimuli or silence. ZENK expression in CMM and NCM was equivalent for song with and without special syllables, but significantly lower for silence. Females who experienced song with special syllables had lower plasma estradiol concentrations after final song playback. This study indicates that CMM exhibits an IEG response bias to special syllables in limited acoustic contexts, but not in full song, which may contain additional biologically relevant information. Furthermore, estradiol concentrations may mediate changes in song responses, serving as a mechanism for modulating mate choice in differing song environments.     

Copulation-solicitation Displays in Female Canaries (Serinus canaria): are Oestradiol Implants Necessary?

The aim of this study was twofold: 1. To study the timing of copulation-solicitation displays (CSD) in female canaries during a natural breeding cycle; 2. To address the question of the adequacy of invasive methods such as oestradiol treatment. Towards these ends, we compared seven oestradiol-implanted and eight control females. Moreover, temporal relationships between reproductive behaviour and plasma concentrations of luteinizing hormone and oestradiol were investigated. The results showed that: 1. CSD appeared about 3 d before egg laying, after the peak of nest building. The maximum number of CSD was observed at the beginning of egg laying. CSD disappeared when the last egg was laid, at the very beginning of incubation; 2. No significant difference was found between the two groups for any behavioural criterion, particularly CSD. No significant difference appeared between control and oestradiol-treated females for luteinizing hormone concentrations. In contrast, oestradiol-implanted females presented higher levels of oestradiol during nest building and during egg laying, 9–13 d after implantation (median 2.53 and 1.47 ng/ml for implanted females vs 0.57 ng/ml and undetectable levels for controls). Implantation had no effect on the progress of nest building, CSD exhibition, egg laying and incubation. Our results suggest that implantation with oestradiol is not necessary in female canary to obtain CSD since they breed readily in captivity and already have enough oestradiol. The similar results in both groups lead one to question the necessity of oestradiol priming in some female choice experiments.     

Female Canaries (Serinus canaria) Associate more with Males that Contrast Strongly against the Background

Male birds with bright plumage colors which entail production costs and increased predation risks should be able to emphasize the handicap function of their ornaments when they present themselves against a contrasting background. Contrast with the background may accentuate the signal's costliness and make the male more conspicuous to predators. Both effects should contribute to increase male attractiveness. It is therefore conceivable that the extent to which the male plumage contrasts against the background modifies female choice behavior as it improves the discrimination of mates. We tested this hypothesis in domesticated canaries (Serinus canaria). In the first experiment, yellow females could choose between two yellow males presented in front of a yellow and a white background, respectively. In the second experiment we replaced the yellow males with white ones. In experiment 1 females associated significantly more with yellow males which contrasted strongly against the white background. In experiment 2 there was at least a trend for preferred associations with the white male in front of the yellow background. We found no support that male properties per se were chosen. We could further clarify that females associated with the contrasting male and not with a particular background color. Thus, our study demonstrates that not only inherent properties of the sender but also the interaction of bird color with the signaling environment may influence mate choice.     

Male Song Quality, Egg Size and Offspring Sex in Captive Canaries (Serinus canaria)

Life history theory predicts that females should vary their investment in offspring according to the quality of their mate. In birds, several studies have now shown that females do vary investment according to perceived male quality, by producing larger eggs, investing more in parental care or by manipulating the sex of their offspring. In a captive breeding colony of canaries, we first show that under normal conditions larger eggs in a clutch are more likely to hatch male offspring. In canaries, male song functions in female attraction and females respond more to complex structures in male song called sexy syllables. In a series of experiments, we go on to show first, that females exposed to playback of male song produce larger eggs than those who heard no song. Next, using synthetic songs, we show that females exposed to playback of more attractive songs containing sexy syllables, produced larger eggs than those exposed to simpler songs containing no sexy syllables. However, in a final analysis, we found no evidence from our experiments that females exposed to playback of more attractive songs also produced more male offspring.     

Sex Differences in Plasma Steroid Concentrations and Singing Behaviour during Ontogeny in Canaries (Serinus canaria)

The relationship between the ontogenetic pattern of sex steroids and the differentiation of sexually dimorphic song in canaries of both sexes was studied. Songs were recorded to assess the temporal course of different developmental stages. Song parameters such as length and frequency of tours were measured. Parallel to behavioural observations, all birds were bled regularly every 20–30 days from the age of 15 days to day 235. The plasma samples were analyzed by RIA to measure testosterone (T), dihydrotestosterone (DHT) and estradiol-17β (E₂). The following results were obtained: 1) In young male canaries we distinguish three different stages of song development: subsong, starting at the age of 30 days, plastic song, and juvenile autumnal song finally giving way to the rigid and stable utterances of the reproductive period in next spring. During ontogeny the length and frequency of tours increase gradually. Female canaries were not observed singing regularly during their first year of life, whereas males sing very frequently. 2) Both sexes show tendencies to elevated titres of testosterone before the onset of juvenile moult. These titres correspond to those of paired males during the reproductive cycle. Song development is not correlated with the ontogenetic pattern of testosterone: the process of crystallization from the amorphic songs uttered by juveniles progresses gradually to the autumnal song in late autumn, when the titres of T in males are low (< 200 pg/ml). Female T and DHT levels during ontogeny correspond to those of the males. 3) There are sex differences in the estradiol pattern. Males show higher titres in several stages of development than females.     

The effect of auditory distractors on song discrimination in male canaries (Serinus canaria)

Male songbirds such as canaries produce complex learned vocalizations that are used in the context of mate attraction and territory defense. Successful mate attraction or territorial defense requires that a bird be able to recognize individuals based on their vocal performance and identify these songs in a noisy background. In order to learn more about how birds are able to solve this problem, we investigated, with a two-alternative choice procedure, the ability of adult male canaries to discriminate between conspecific song segments from two different birds and to maintain this discrimination when conspecific songs are superimposed with a variety of distractors. The results indicate that male canaries have the ability to discriminate, with a high level of accuracy song segments produced by two different conspecific birds. Song discrimination was partially maintained when the stimuli were masked by auditory distractors, but the accuracy of the discrimination progressively declined as a function of the number of masking distractors. The type of distractor used in the experiments (other conspecific songs or different types of artificial white noise) did not markedly affect the rate of deterioration of the song discrimination. These data indicate that adult male canaries have the perceptual abilities to discriminate and selectively attend to one ongoing sound that occurs simultaneously with one or more other sounds. The administration of a noradrenergic neurotoxin did not impair markedly the discrimination learning abilities although the number of subjects tested was too small to allow any firm conclusion. In these conditions, however, the noradrenergic lesion significantly increased the number failures to respond in the discrimination learning task suggesting a role, in canaries, of the noradrenergic system in some attentional processes underlying song learning and processing.     

Progesterone inhibits female courtship behavior in domestic canaries (Serinus canaria)

We studied copulation solicitation display (CSD) responses to playback in photostimulated female canaries given systemic injections of progesterone. Eight females received injections of 0.1 mg of progesterone dissolved in olive oil during their first breeding cycle and were untreated during their second breeding cycle; eight females received only the oil vehicle during their first breeding cycle and received no treatment during their second breeding cycle. The injections were performed every second day during 15 days, after the onset of nest building. Progesterone treatment resulted in a significant increase of plasma progesterone which in turn provoked an inhibition of females' CSDs and decreased the size of the clutch. During the first breeding cycle, progesterone-treated females had lower CSDs and egg-laying scores than did control females. During the second breeding cycle, when females received no treatment, no differences emerged between the two groups. The suppressive effect of progesterone on female sexual responses was observed as soon as 48 h after the beginning of the treatment. We propose that progesterone plays a key role in mediating the transition from active female courtship behavior to sexual refractoriness in this species. Suppressive effects of progesterone on female sexual behavior have been previously described in lizards as well as in rodents. Our data are consistent with the hypothesis of Godwin et al. (J. Godwin, V. Hartman, M. Grammer, and D. Crews, Horm. Behav. 30, 138-144, 1996) which proposed that the decrease in sexual behavior following plasma progesterone increase represents an evolutionarily conserved mechanism in the regulation of female sexual behavior.     

Isospora canaria Box, 1975 (Apicomplexa: Eimeriidae) from canaries Serinus canaria Linnaeus (Passeriformes: Fringillidae) in Brazil

Isospora canaria Box, 1975 (Protozoa, Apicomplexa, Eimeriidae) is reported and described from canaries Serinus canaria (Linnaeus) in southeast Brazil. Its oöcysts are subspheroidal to ellipsoidal, 24.4 × 22.2 μm, with smooth, bilayered wall, ~1.2 μm. The micropyle and the oöcyst residuum are absent, but a polar granule is present. The sporocysts are lemon-shaped, 17.6 × 10.6 μm. The Stieda body is nipple-like, and substieda body is prominent and homogeneous. The sporocyst residuum is composed of scattered granules. The sporozoite has anterior and posterior refractile bodies and a nucleus. The report of this coccidium recovered from exotic canaries in South America is relevant to native passerines, mainly to Carduelis yarrellii, which are listed as vulnerable species by IUCN (International Union for Conservation of Nature and Natural Resources).     

Mate preferences in female canaries (Serinus canaria) within a breeding season

Divorce and remating in birds can be described as strategies used to enhance reproductive success. Mate switching often occurs because pairs failed to brood at least one chick during the previous breeding season. In the present study, we evaluated the influence of reproductive success on female preferences in domesticated canaries (Serinus canaria). For that purpose, females previously paired and having reared young were placed in a choice test situation: They were allowed to choose between their previous mate and a familiar male (a male neighbor during the breeding period). During these choice tests, females tended to stay near their previous mate longer than near a male neighbor when their reproductive success was “good” (at least two chicks). On the other hand, females with “poor” reproductive success (one chick) did not show a preference for their previous mate. Furthermore, in the present study, we observed that during choice tests males reacted to the presence of their previous mate in a particular way, by gathering nest material. This behavior was more scarcely observed in neighbor males which, on the contrary, sang significantly more than previous mates did.     

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.     

Multisensory non-photoperiodic cue advances the onset of seasonal breeding in Island canaries (Serinus canaria)

In most temperate zone vertebrates, photoperiodic change plays the major role in the timing of seasonal breeding. However, direct environmental stimuli such as temperature, rainfall, or availability of food are thought to be important for fine-tuning breeding activities. Building on evidence from wild Island canaries (Serinus canaria), the authors had shown advancing effects of green vegetation on breeding under captive, short-day conditions. So far, the precise, sensory modalities of this stimulatory cue are unknown. Here the authors present new data that confirm advanced breeding activities in the presence of green vegetation and narrow its stimulatory components. They found that direct exposure of the birds to fresh green vegetation represented the strongest stimulus and advanced breeding by up to 2 months compared to controls. In contrast, access to artificial green vegetation, extracts from green vegetation, or olfactory components alone had no such effects. This is, to the best of the authors' knowledge, the first experiment that examines sensory components of an effective, supplementary, non-photoperiodic cue in a temperate zone species. The data suggest that in order to use non-photoperiodic information to time breeding, birds must be able to integrate and process multisensory stimuli. Single non-photoperiodic sensory cues are insufficient to affect the timing of seasonal breeding.     

Preferences and predispositions of female canaries (Serinus canaria) for loud intensity of male sexy phrases

In the present study, we tested the effect of song amplitude on intersexual relationships. To evaluate preferences and predispositions of female canaries for amplitude levels of male song, we conducted two experiments using both females raised in acoustic isolation and females raised in an aviary under 'normal' acoustic conditions. The songs used in both experiments followed the same pattern: one reactive phrase surrounded by two nonreactive phrases. The first experiment consisted of testing female preferences for weak, normal, or loud amplitudes of the reactive phrase (i.e. these reactive phrases provoke sexual stimulation in females). In a second experiment, we tested female preferences for weak, normal, or loud amplitudes of the nonreactive phrases. These two experiments allowed us to evaluate female preferences for intensity levels of reactive and nonreactive phrases. In the first experiment, all females significantly prefered loud and normal reactive phrases, whereas the second experiment showed that loud nonreactive phrases do not necessarily provoke more responses than other nonreactive phrases. Female canaries were, thus, more stimulated by the intensity level of a particular part of the song. Both females raised in acoustic isolation and in normal acoustic conditions responded in the same way. We can therefore suppose that learning, through acoustic experience, has little influence on preference development for amplitude levels.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 808–814.     

Syllable repertoire and the size of the song control system in captive canaries (Serinus canaria)

In songbirds, there is considerable interest in relationships between song structure and the size of the song control system in the forebrain. In male canaries, earlier studies have reported that repertoire size increased with age, and positive correlations were obtained between repertoire size and the volume of song control nuclei such as high vocal center (HVC). Here we investigate whether age has an effect upon both the song structure and the morphology of two song control nuclei [HVC and robustus archistriatalis (RA)] that are important in song production. We recorded songs from an aviary population of 1- and 2-year-old male domesticated canaries. We found that repertoire size, number of sexually attractive (sexy) syllables, and size of song nuclei did not differ between 1- and 2-year-old males. Neither did we find significant correlations between syllable repertoire size and the size of the song control nuclei. However, HVC size was positively correlated with the proportion of sexy syllables in the repertoires of 2-year-old males. Some older males may enhance vocal performance by modifying the control of syllables rather than by increasing repertoire size or neural space.     

Coordinated and dissociated effects of testosterone on singing behavior and song control nuclei in canaries (Serinus canaria)

Temperate zone songbirds that breed seasonally exhibit pronounced differences in reproductive behaviors including song inside and outside the breeding season. Springlike long daylengths are associated with increases in plasma testosterone (T) concentrations, as well as with increases in singing and in the volume of several brain nuclei known to control this behavior. The mechanisms whereby T can induce changes in behavior and brain, and whether or not these effects are differentially regulated, have recently begun to be examined, as has the question of the relative contributions of T and its androgenic and estrogenic metabolites to the regulation of this seasonal behavioral and neural plasticity. In this experiment, we examined the effects of T, 5alpha-dihydrotestosterone, or 17beta-estradiol treatment on castrated male canaries housed on short days and compared neural and behavioral effects in these males to similarly-housed males given only blank implants. We observed that only T treatment was effective in eliciting significant increases in singing behavior after 11 days of hormone exposure. In addition, T alone was effective in increasing the volume of a key song production nucleus, HVC. However, at this time, none of the steroids had any effects on the volumes of two other song control nuclei, Area X of the medial striatum and the robust nucleus of the arcopallium (RA), that are efferent targets of HVC, known to be regulated by androgen in canaries and also to play a role in the control of adult song. T can thus enhance singing well before concomitant androgen-induced changes in the song control system are complete.     

Social context affects testosterone-induced singing and the volume of song control nuclei in male canaries (Serinus canaria)

The contribution of social factors to seasonal plasticity in singing behavior and forebrain nuclei controlling song, and their interplay with gonadal steroid hormones are still poorly understood. In many songbird species, testosterone (T) enhances singing behavior but elevated plasma T concentrations are not absolutely required for singing to occur. Singing is generally produced either to defend a territory or to attract a mate and it is therefore not surprising that singing rate can be influenced by the sex and behavior of the social partner. We investigated, based on two independent experiments, the effect of the presence of a male or female partner on the rate of song produced by male canaries. In the first experiment, song rate was measured in dyads composed of one male and one female (M-F) or two males (M-M). Birds were implanted with T-filled Silastic capsules or with empty capsules as control. The number of complete song bouts produced by all males was recorded during 240 min on week 1, 2, 4, and 8 after implantation. On the day following each recording session, brains from approximately one-fourth of the birds were collected and the volumes of the song control nuclei HVC and RA were measured. T increased the singing rate and volume of HVC and RA but these effects were affected by the social context. Singing rates were higher in the M-M than in the M-F dyads. Also, in the M-M dyads a dominance-subordination relationship soon became established and dominant males sang at higher rates than subordinates in T-treated but not in control pairs. The differences in song production were not reflected in the size of the song control nuclei: HVC was larger in M-F than in M-M males and within the M-M dyads, no difference in HVC or RA size could be detected between dominant and subordinate males. At the individual level, the song rate with was positively correlated with RA and to a lower degree HVC volume, but this relationship was observed only in M-M dyads, specifically in dominant males. A second experiment, carried out with castrated males that were all treated with T and exposed either to another T-treated castrate or to an estradiol-implanted female, confirmed that song rate was higher in the M-M than in the M-F condition and that HVC volume was larger in heterosexual than in same-sex dyads. The effects of T on singing rate and on the volume of the song control nuclei are thus modulated by the social environment, including the presence/absence of a potential mate and dominance status among males.     

Hatching asynchrony aggravates inbreeding depression in a songbird (Serinus canaria): An inbreeding–environment interaction

Understanding how the intensity of inbreeding depression is influenced by stressful environmental conditions is an important area of enquiry in various fields of biology. In birds, environmental stress during early development is often related to hatching asynchrony; differences in age, and thus size, impose a gradient in conditions ranging from benign (first hatched chick) to harsh (last hatched chick). Here, we compared the effect of hatching order on growth rate in inbred (parents are full siblings) and outbred (parents are unrelated) canary chicks (Serinus canaria). We found that inbreeding depression was more severe under more stressful conditions, being most evident in later hatched chicks. Thus, consideration of inbreeding‐environment interactions is of vital importance for our understanding of the biological significance of inbreeding depression and hatching asynchrony. The latter is particularly relevant given that hatching asynchrony is a widespread phenomenon, occurring in many bird species. The exact causes of the observed inbreeding‐environment interaction are as yet unknown, but may be related to a decrease in maternal investment in egg contents with laying position (i.e. prehatching environment), or to performance of the chicks during sibling competition and/or their resilience to food shortage (i.e. posthatching environment).     

No Correlation Between Song and Circulating Testosterone Levels During Multiple Broods in the Domesticated Canary (Serinus canaria)

In anticipation of the breeding season male songbirds of the temperate zones undergo gonadal recrudescence in early spring that lead to elevated circulating testosterone (T) levels, positively correlated with an increase in aggressive and song behaviour. However, besides seasonal changes there are also marked fluctuations of T levels and song production within the breeding season. In many species, T levels and singing activity drop after pairing or after the first clutch is laid. Domesticated canaries (Serinus canaria) are multiple‐brooded with an extended breeding season, and males continue to sing after egg‐laying. So far, studies have mainly focused on the seasonality of T levels and song behaviour whereas the pattern of change throughout the breeding period is unknown. Here, we focused on the first and on the last brood of the breeding season. We measured plasma T levels in males at the different breeding stages and assessed song characteristics of males at both times. T levels fluctuated significantly throughout brood 1, being highest during the nest building stage compared with egg‐laying and feeding of young. No such changes occurred during the last brood. Temporal song characteristics changed between brood 1 and brood 3 with song length being the main contributor to explain these changes. Our data suggest that T mainly plays a role in mate attraction and initial nesting site selection but that elevated levels are not necessary for subsequent breeding attempts. Furthermore, temporal song characteristics are maintained independently of T levels, suggesting a threshold effect. Our results demonstrate behavioural and physiological plasticity of domesticated canaries during the breeding season and are consistent with previous findings in wild songbirds.