Song Behavior Research Articles

Regulatory mechanisms of testosterone-stimulated song in the sensorimotor nucleus HVC of female songbirds

BackgroundIn male birds, influence of the sex steroid hormone testosterone and its estrogenic metabolites on seasonal song behavior has been demonstrated for many species. In contrast, female song was only recently recognized to be widespread among songbird species, and to date, sex hormone effects on singing and brain regions controlling song development and production (song control nuclei) have been studied in females almost exclusively using domesticated canaries (Serinus canaria). However, domesticated female canaries hardly sing at all in normal circumstances and exhibit only very weak, if any, song seasonally under the natural photoperiod. By contrast, adult female European robins (Erithacus rubecula) routinely sing during the winter season, a time when they defend feeding territories and show elevated circulating testosterone levels. We therefore used wild female European robins captured in the fall to examine the effects of testosterone administration on song as well as on the anatomy and the transcriptome of the song control nucleus HVC (sic). The results obtained from female robins were compared to outcomes of a similar experiment done in female domesticated canaries.ResultsTestosterone treatment induced abundant song in female robins. Examination of HVC transcriptomes and histological analyses of song control nuclei showed testosterone-induced differentiation processes related to neuron growth and spacing, angiogenesis and neuron projection morphogenesis. Similar effects were found in female canaries treated with testosterone. In contrast, the expression of genes related to synaptic transmission was not enhanced in the HVC of testosterone treated female robins but was strongly up-regulated in female canaries. A comparison of the testosterone-stimulated transcriptomes indicated that brain-derived neurotrophic factor (BDNF) likely functions as a common mediator of the testosterone effects in HVC.ConclusionsTestosterone-induced singing of female robins correlated with cellular differentiation processes in the HVC that were partially similar to those seen in the HVC of testosterone-treated female canaries. Other modes of testosterone action, notably related to synaptic transmission, appeared to be regulated in a more species-specific manner in the female HVC. Divergent effects of testosterone on the HVC of different species might be related to differences between species in regulatory mechanisms of the singing behavior.Electronic supplementary materialThe online version of this article (doi:10.1186/s12868-014-0128-0) contains supplementary material, which is available to authorized users.

Reversing song behavior phenotype: Testosterone driven induction of singing and measures of song quality in adult male and female canaries (Serinus canaria)

In songbirds, such as canaries (Serinus canaria), the song control circuit has been shown to undergo a remarkable change in morphology in response to exogenous testosterone (T). It is also well established that HVC, a telencephalic nucleus involved in song production, is significantly larger in males than in females. T regulates seasonal changes in HVC volume in males, and exposure to exogenous T in adult females increases HVC volume and singing activity such that their song becomes more male-like in frequency and structure. However, whether there are sex differences in the ability of T to modulate changes in the song system and song behavior has not been investigated in canaries. In this study, we compared the effects of increasing doses of T on singing and song control nuclei volumes in adult male and female American Singer canaries exposed to identical environmental conditions. Males were castrated and all birds were placed on short days (8L:16D) for 8weeks. Males and females were implanted either with a 2, 6 or 12mm long Silastic™ implant filled with crystalline T or an empty 12mm implant as control. Birds were then housed individually in sound-attenuated chambers. Brains were collected from six birds from each group after 1week or 3weeks of treatment. Testosterone was not equally effective in increasing singing activity in both males and females. Changes in song quality and occurrence rate took place after a shorter latency in males than in females; however, females did undergo marked changes in a number of measures of song behavior if given sufficient time. Males responded with an increase in HVC volume at all three doses. In females, T-induced changes in HVC volume only had limited amplitude and these volumes never reached male-typical levels, suggesting that there are sex differences in the neural substrate that responds to T.

Reactive neurogenesis in response to naturally occurring apoptosis in an adult brain.

Neuronal birth and death are tightly coordinated to establish and maintain properly functioning neural circuits. Disruption of the equilibrium between neuronal birth and death following brain injury or pharmacological insult often induces reactive, and in some cases regenerative, neurogenesis. Many neurodegenerative disorders are not injury-induced, however, so it is critical to determine if and how reactive neurogenesis occurs under noninjury-induced neurodegenerative conditions. Here, we used a model of naturally occurring neural degradation in a neural circuit that controls song behavior in Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) and examined the temporal dynamics between neuronal birth and death. We found that during seasonal-like regression of the song, control nucleus HVC (proper name), caspase-mediated apoptosis increased within 2 d following transition from breeding to nonbreeding conditions and neural stem-cell proliferation in the nearby ventricular zone (VZ) increased shortly thereafter. We show that inhibiting caspase-mediated apoptosis in HVC decreased neural stem-cell proliferation in the VZ. In baseline conditions the extent of neural stem-cell proliferation correlated positively with the number of dying cells in HVC. We demonstrate that as apoptosis increased and the number of both recently born and pre-existing neurons in HVC decreased, the structure of song, a learned sensorimotor behavior, degraded. Our data illustrate that reactive neurogenesis is not limited to injury-induced neuronal death, but also can result from normally occurring degradation of a telencephalic neural circuit.

Male mate preferences in mutual mate choice: finches modulate their songs across and within male–female interactions

Male songbirds use song to advertise their attractiveness as potential mates, and the properties of those songs have a powerful influence on female mate preferences. One idea is that males may exert themselves maximally in each song performance, consistent with female evaluation and formation of mate preferences being the primary contributors to mate choice. Alternatively, males may modulate their song behaviour to different degrees in the presence of different females, consistent with both male and female mate preferences contributing to mutual mate choice. Here we consider whether male Bengalese finches, Lonchura striata domestica, express mate preferences at the level of individual females, and whether those preferences are manifest as changes in song behaviour that are sufficient to influence female mate choice. We tested this idea by recording songs performed by individual unmated males during a series of 1 h interactions with each of many unmated females. Across recording sessions, males systematically varied both the quantity and the quality of the songs that they performed to different females. Males also varied their song properties throughout the course of each interaction, and behavioural tests using female birds revealed that songs performed at the onset of each interaction were significantly more attractive than songs performed by the same male later during the same interaction. This demonstration of context-specific variation in the properties of male reproductive signals and a role for that variation in shaping female mate preference reveals that male mate preferences play an important role in mutual mate choice in this species. Because these birds thrive so well in the laboratory and are so amenable to observation and experimentation across generations, these results yield a new model system that may prove especially advantageous in disentangling the role of male and female mate preferences in shaping mutual mate choice and its long-term benefits or consequences.

Dissociable effects of social context on song and doublecortin immunoreactivity in male canaries.

Variation in environmental factors such as day length and social context greatly affects reproductive behavior and the brain areas that regulate these behaviors. One such behavior is song in songbirds, which males use to attract a mate during the breeding season. In these species the absence of a potential mate leads to an increase in the number of songs produced, while the presence of a mate greatly diminishes singing. Interestingly, although long days promote song behavior, producing song itself can promote the incorporation of new neurons in brain regions controlling song output. Social context can also affect such neuroplasticity in these song control nuclei. The goal of the present study was to investigate in canaries (Serinus canaria), a songbird species, how photoperiod and social context affect song and the incorporation of new neurons, as measured by the microtubule-associated protein doublecortin (DCX) in HVC, a key vocal production brain region of the song control system. We show that long days increased HVC size and singing activity. In addition, male canaries paired with a female for 2 weeks showed enhanced DCX-immunoreactivity in HVC relative to birds housed alone. Strikingly, however, paired males sang fewer songs that exhibited a reduction in acoustic features such as song complexity and energy, compared with birds housed alone, which sang prolifically. These results show that social presence plays a significant role in the regulation of neural and behavioral plasticity in songbirds and can exert these effects in opposition to what might be expected based on activity-induced neurogenesis.

Effects of nicotine administration on spectral and temporal features of crystallized song in the adult male zebra finch.

The process through which the zebra finch (Taeniopygia guttata) acquires and produces crystallized song has long been thought of as highly analogous to the process through which humans acquire and produce speech. Nicotinic acetylcholine receptors are present in song nuclei that play important roles in song production and/or acquisition. We studied the effect of in vivo nicotine on temporal and spectral features of crystallized song. We used 16 adult male zebra finches that were exposed to an established 7-day nicotine or saline treatment. Song behavior was monitored for a 2-month period following the cessation of the nicotine/saline treatment. All animals served as their own control in order to determine whether any song characteristics changed over the observed time period compared to the baseline measurement. Inter-syllable duration and Wiener entropy were significantly affected by the in vivo administration of nicotine. These observed changes persisted for a 2-month period following the cessation of nicotine exposure. Similar changes were not observed in the age-matching control group. Nicotine significantly affected tempo and rhythm of the crystallized zebra finch song. We believe that this in vivo nicotine-exposed zebra finch model can not only provide a further understanding of the underlying behavioral mechanisms of the cognitive implications of nicotine dependence but also help in the development of therapeutics targeting cognitive deficits often observed during nicotine withdrawal.

Geographic variation in songs of the Common Yellowthroat

ABSTRACT The Common Yellowthroat (Geothlypis trichas) exhibits widespread geographic variation in plumage, morphology, migratory behavior, and song. In addition, researchers recently found evidence that the Common Yellowthroat has three genetically distinct groups across its North American range: eastern, western, and southwestern. These groups are more genetically similar to other Geothlypis species than to each other, which suggests relatively long-term isolation. I hypothesized that geographic variation in song behavior should reflect these genetic differences. To test this hypothesis, I examined spatial patterns of variation in both note types and acoustic characteristics of song. Consistent with the hypothesis, I found significant differences among the three groups, particularly in frequency measures, internote duration, notes per phrase, and note elaborateness. Within the eastern and western groups, I also found significant song differences among historically recognized subspecies. When comparing we...

The role of the pineal gland in the photoperiodic control of bird song frequency and repertoire in the house sparrow, Passer domesticus

Temperate zone birds are highly seasonal in many aspects of their physiology. In mammals, but not in birds, the pineal gland is an important component regulating seasonal patterns of primary gonadal functions. Pineal melatonin in birds instead affects seasonal changes in brain song control structures, suggesting the pineal gland regulates seasonal song behavior. The present study tests the hypothesis that the pineal gland transduces photoperiodic information to the control of seasonal song behavior to synchronize this important behavior to the appropriate phenology. House sparrows, Passer domesticus, expressed a rich array of vocalizations ranging from calls to multisyllabic songs and motifs of songs that varied under a regimen of different photoperiodic conditions that were simulated at different times of year. Control (SHAM) birds exhibited increases in song behavior when they were experimentally transferred from short days, simulating winter, to equinoctial and long days, simulating summer, and decreased vocalization when they were transferred back to short days. When maintained in long days for longer periods, the birds became reproductively photorefractory as measured by the yellowing of the birds' bills; however, song behavior persisted in the SHAM birds, suggesting a dissociation of reproduction from the song functions. Pinealectomized (PINX) birds expressed larger, more rapid increases in daily vocal rate and song repertoire size than did the SHAM birds during the long summer days. These increases gradually declined upon the extension of the long days and did not respond to the transfer to short days as was observed in the SHAM birds, suggesting that the pineal gland conveys photoperiodic information to the vocal control system, which in turn regulates song behavior.

Testosterone influences song behaviour and social dominance – But independent of prenatal yolk testosterone exposure

In the last two decades, maternally derived yolk androgens have been shown to significantly alter offspring development, and a number of these effects persist into adulthood. However, little is known about their underlying mechanisms. Mechanisms that have been suggested are changes in the endogenous androgen production post-hatching or changes in the sensitivity towards circulating androgens.We tested the effects of yolk testosterone on the plasma testosterone levels and the sensitivity to testosterone in 5months old male canaries that hatched from eggs that were either injected with testosterone (yT-males) or with a control solution (yC-males). Changes in sensitivity were investigated via the behavioural response to an experimental elevation of the plasma testosterone levels. We performed the experiment in fall (low endogenous testosterone production), focusing on testosterone dependent response traits (aggression and song).Before implantation, there was a non-significant trend that the plasma testosterone levels were lower in yT-males than in yC-males. Elevating the plasma testosterone concentrations increased aggressiveness, song bout length and similarity of repeated song elements (=consistency), with the latter likely being a consequence of testosterone-driven song crystallization. However, these effects were not different among yT- or yC-males in any of the parameters. Thus, our findings render it unlikely that changes in the sensitivity to testosterone post-hatching would form the main underlying mechanism of hormone-mediated maternal effects in birds. Further experiments are urgently needed in order to understand the nature of the phenotypic effects resulting from embryonic exposure to maternal yolk testosterone.

Sexually dimorphic perineuronal net expression in the songbird

Sexual dimorphism of song behavior and its underlying brain architecture characterizes the vocal learning system of many songbirds (Nottebohm and Arnold [1] and Ball and MacDougall-Shackleton [2]). Females do not sing and their neural song control system is reduced compared to males. However, females do learn to discriminate male song during a sensitive period (Clayton [3] and Nelson et al. [4]). We reasoned that any song nuclei that might store developmental social learning in female zebra finches would be marked by extracellular perineuronal nets (PNNs), which limit plasticity at the ends of critical periods (Hockfield et al. [5] and Hensch [6]), stabilize learning (Wang and Fawcett [7]), and demarcate all song nuclei in male finches (Balmer et al. [8]). PNN expression patterns in four brain areas were compared in males and females: the Lateral Magnocellular Nucleus (LMAN) and a basal ganglia region that contains Area X in males, which together constitute an anterior cortical-basal ganglia pathway necessary for male song plasticity, and HVC and the Robust Nucleus of the Arcopallium (RA), which together form a posterior pathway that is critical for song production in males. We found a dichotomy of PNN expression in the female song system: the anterior cortical-basal ganglia pathway was highly enriched for PNNs and indistinguishable from males, whereas the posterior pathway was essentially devoid of PNNs. These data indicate that social signaling in the female song system may undergo a true critical period, similar to sensory systems, and that limiting this critical period selectively involves the song cortical-basal ganglia pathway.

MiR-9 and miR-140-5p TargetFoxP2and Are Regulated as a Function of the Social Context of Singing Behavior in Zebra Finches

Mutations in the FOXP2 gene cause speech and language impairments, accompanied by structural and functional abnormalities in brain regions underlying speech-related sensory-motor processing, including the striatum and cerebellum. The sequence and expression patterns of FOXP2 are highly conserved among higher vertebrates. In the zebra finch brain, FoxP2 is expressed in Area X, a striatal nucleus required for vocal learning, and reduced FoxP2 expression impairs dendritic development and vocal learning. The FoxP2 gene encodes a transcription factor that controls the expression of many downstream genes. However, how FOXP2 gene expression is regulated is not clearly understood. miRNAs regulate gene expression post-transcriptionally by targeting the 3'-untranslated regions (UTRs) of mRNAs, leading to translational suppression or mRNA degradation. In this study, we identified miR-9 and miR-140-5p as potential regulators of the FoxP2 gene. We show that both miR-9 and miR-140-5p target specific sequences in the FoxP2 3'-UTR and downregulate FoxP2 protein and mRNA expression in vitro. We also show that the expression of miR-9 and miR-140-5p in Area X of the zebra finch brain is regulated during song development in juvenile zebra finches. We further show that in adult zebra finches the expression of miR-9 and miR-140-5p in Area X is regulated as a function of the social context of song behavior in males singing undirected songs. Our findings reveal a post-transcriptional mechanism that regulates FoxP2 expression and suggest that social vocal behavior can influence the basal ganglia circuit controlling vocal learning via a miRNA-FoxP2 gene regulatory network.

Parental Provisioning by Carolina Wrens

We studied nestling provisioning and male song behavior associated with provisioning by Carolina Wrens (Thryothorus ludovicianus) throughout the nestling period. Overall, males and females (n = 14 pairs) provisioned at similar rates throughout four nestling stages although males tended to provision more at the earliest nest stage (1–3 days). Males and females increased their rate of provisioning progressively over the nestling period. Parents brought one food item at a time to the nest and load sizes were similar between males and females, and between early and late nest stages. Males sang 34% of the time on arrival at nests to provision and 49% on leaving nests after provisioning. There was no relationship between male song and age of the nestlings. Males sang more after provisioning nestlings when females were not present (55%) than when females were present (33%) at the nest. The function of male song during provisioning may be to communicate the male's location to the female and to indicate he has recently provisioned the nestlings but this requires further study.

How social experience shapes song representation in the brain of starlings

Birdsong, like speech, is a learned behaviour whose critical function is to communicate with others and whose development critically depends on social influences. Song learning is a complex phenomenon that involves not only the development of species-specific vocalisations, but also the development of the ability to organise these vocalisations and to use them in an appropriate context. Although the fact that interactions with adult experienced models are essential for song production to develop properly has been well established, far less is known about song perception and processing. The fact that songbirds learn to vocalise and to use their vocalisations selectively through interactions with adults questions whether such interactions are also required for songbirds to perceive and process their vocalisations selectively and whether social interactions may shape song perception and processing as they shape song production. In order to address these questions, our team uses an original neuroethological approach to study the neural bases of song behaviour in a highly social songbird species: the European starlings. We provide here a synthesis of the results we have obtained using this approach over the last decade. Our results show that direct social experience with adult experienced models not only shapes song behaviour but also shapes these songbirds’ brains and their ability to perceive and to process acoustic signals whose communicative value, as well as their acoustic structure, have to be learned.

Songs of two starling species: common traits versus adaptations to the social environment

We analysed, for the first time, songs of the African Red-winged Starling Onychognathus morio and compared their general characteristics with those of the European Starling Sturnus vulgaris. Both species are gregarious during the non-breeding season, but European Starlings tend to nest in colonies, form unstable pair-bonds and are occasionally polygynous, whereas Red-winged Starlings form long-term pair-bonds and occupy exclusive nesting territories. Red-winged Starlings produced the same basic song categories as European Starlings: warbles and whistles. These two categories appeared to be involved in similar social interactions in the two species. However, several aspects of song behaviour differed between the two species: Red-winged Starlings, breeding in isolated nests, preferentially used whistles for long-distance communication and showed a simpler organization of warbling song. Whistles in the Red-winged Starling were mostly shared between birds and, in contrast to the European Starling, were not indicators of individual identity. Also in contrast to the European Starling, female song in Red-winged Starlings appeared very important throughout the breeding period. Our results suggest that some song characteristics in the two species are phylogenetically conserved whereas others are affected by the distinct social systems of the two species.

Testosterone-dependency of male solo song in a duetting songbird — Evidence from females

For male songbirds of the temperate zone there is a tight link between seasonal song behaviour and circulating testosterone levels. Such a relationship does not seem to hold for tropical species where singing can occur year-round and breeding seasons are often extended. White-browed sparrow weavers (Plocepasser mahali) are cooperatively breeding songbirds with a dominant breeding pair and male and female subordinates found in eastern and southern Africa. Each group defends an all-purpose territory year-round. While all group members sing duets and choruses, the most dominant male additionally sings a solo song that comprises a distinct and large syllable repertoire. Previous studies suggested this type of song being associated with reproduction but failed to support a relationship with males' circulating testosterone levels. The present study aimed to investigate the steroid hormone sensitivity of the solo song in more detail. We found that dominant males had significantly higher circulating testosterone levels than subordinates during the early and late breeding seasons. No changes in solo song characteristics were found between both time points. Further, experimental implantation of captive adult females with exogenous testosterone induced solo singing within one week of treatment. Such females produced male-typical song regarding overall structure and syllable composition. Sex differences existed, however, concerning singing activity, repertoire size and temporal organisation of song. These results suggest that solo singing in white-browed sparrow weavers is under the control of gonadal steroid hormones. Moreover, the behaviour is not male-specific but can be activated in females under certain conditions.

Song in the cold is ‘hot’: memory of and preference for sexual signals perceived under thermal challenge

The environmental conditions under which signals are perceived can affect receiver responses. Many songbird populations produce a song chorus at dawn, when, in cold habitats, they would experience thermal challenge. We recorded temperature and the song activity of Lincoln's sparrows (Melospiza lincolnii) on a high-elevation meadow, and determined that song behaviour is concentrated around the coldest time of the day, at dawn. We hypothesized that this is because male song in the cold is more attractive to females than song in the warm. To test this, we exposed laboratory-housed Lincoln's sparrow females to songs at 1°C and 16°C, which they naturally experience in the wild. Females spent 40 per cent more time close to the speaker during playback at 1°C than at 16°C. When tested at 16°C 1-2 days later, females biased their movement towards the speaker playing songs previously heard at 1°C over 16°C. Thus, female Lincoln's sparrows remembered and affiliated with songs they heard under thermal challenge, indicating that the thermal environment can affect the attractiveness of a sexual signal.

Male great tit song perch selection in response to noise‐dependent female feedback

Summary1. Anthropogenic noise can affect intra‐pair communication and therefore interfere with reproductive success. However, many animals have various signal strategies to cope with noise, although it is unclear whether they rely on direct auditory feedback from their own perception of noise or signal‐to‐noise level or on indirect social feedback from receivers.2. We studied the role of social feedback on male great tit (Parus major) song adjustment by exclusively exposing females to artificial traffic noise inside their nest box.3. We found a delay in female response latencies to male song in the noisy condition compared to the control condition on the first day of noise exposure. Males from the noise treatment group, not directly exposed to noise themselves, sang closer to the nest box within 3 days after the start of exposure.4. The male's closer proximity to the nest box most likely led to the observed higher song amplitudes at the noisy nest boxes compared to quiet control nest boxes, and explains why the inside signal‐to‐noise ratios were restored to equal levels between treatment and control nest boxes after several days of exposure.5. The initial difference between treatment groups in female response latencies at the start of exposure also disappeared accordingly.6. Our results strongly suggest an active role for female birds in steering male song behaviour under noisy conditions. Males did not receive direct exposure during intra‐pair communication, but adjusted their behaviour in the predicted direction. These data are important to understand the mechanisms related to communication in noise and reveal the critical role of ecology in shaping animal interactions.

Morphology of axonal projections from the high vocal center to vocal motor cortex in songbirds

Only birds that learn complex vocalizations have telencephalic brain regions that control vocal learning and production, including HVC (high vocal center), a cortical nucleus that encodes vocal motor output in adult songbirds. HVC projects to RA (robust nucleus of the arcopallium), a nucleus in motor cortex that in turn projects topographically onto hindbrain neurons innervating vocal muscles. Individual neurons projecting from HVC to RA (HVC(RA) ) fire sparsely to drive RA activity during song production. To advance understanding of how individual HVC neurons encode production of learned vocalizations, we reconstructed single HVC axons innervating RA in adult male zebra finches. Individual HVC(RA) axons were not topographically organized within RA: 1) axon arbors of HVC cell bodies located near each other sent branches to different subregions of RA, and 2) branches of single HVC axons terminated in different locations within RA. HVC(RA) axons also had a simple, sparse morphology, suggesting that a single HVC neuron activates a limited population of postsynaptic RA neurons. These morphological data are consistent with previous work showing that single HVC(RA) neurons burst sparsely for a brief period of time during the production of a song, indicating that ensembles of HVC(RA) neurons fire simultaneously to drive small temporal segments of song behavior. We also examined the morphology of axons projecting from HVC to RA cup, a region surrounding RA that receives input from auditory cortex. Axons projecting to RA cup also sent some branches into RA, suggesting direct integration between the sensory and motor circuits for song control.

Striatal dopamine modulates song spectral but not temporal features through D1 receptors

The activity of midbrain dopaminergic neurons and their projection to the basal ganglia (BG) are thought to play a critical role in the acquisition of motor skills through reinforcement learning, as well as in the expression of learned motor behaviors. The precise role of BG dopamine (DA) in mediating and modulating motor performance and learning, however, remains unclear. In songbirds, a specialized portion of the BG is responsible for song learning and plasticity. Previously we found that DA acts on D1 receptors in Area X to modulate the BG output signal and thereby trigger changes in song variability. Here, we investigate the effect of D1 receptor blockade in the BG on song behavior in the zebra finch. We report that this manipulation abolishes social context-dependent changes in variability not only in harmonic stacks, but also in other types of syllables. However, song timing seems not to be modulated by this BG DA signal. Indeed, injections of a D1 antagonist in the BG altered neither song duration nor the change of song duration with social context. Finally, D1 receptor activation in the BG was not necessary for the modulation of other features of song, such as the number of introductory notes or motif repetitions. Together, our results suggest that activation of D1 receptors in the BG is necessary for the modulation of fine acoustic features of song with social context, while it is not involved in the regulation of song timing and structure at a larger time scale.

Testosterone stimulates the expression of male-typical socio-sexual and song behaviors in female budgerigars (Melopsittacus undulatus): An experimental study

The hormonal control of sex differences in behavior has been extensively studied, particularly in mammals and birds. Studies have shown that the activational potential of the androgenic sex steroid testosterone (T) on male-typical behaviors in females seems to be species- as well as behavior-specific in birds. It is therefore important to study the activational effects of T in a great variety of bird species and on a wide range of behaviors, preferably in social conditions that favor their expression. Here, we investigated the activational effects of T on vocal, socio-sexual (i.e. affiliative and non-vocal courtship behaviors), aggressive and approach behavior in females of the budgerigar, Melopsittacus undulatus, a highly social monogamous parrot species. We experimentally supplemented T-females with male-like plasma T levels compared to controls. First, we observed females when they were individually housed. We found that T-females performed male-like levels of warbling song, sang significantly longer, but not more song bouts and produced more socio-sexual behaviors than controls. Then, we consecutively confronted females with a female, a dummy, and a male conspecific. T-females showed a significantly shorter latency to interact in all three social contexts. In both intrasexual and intersexual contexts, T-females performed significantly higher levels of approach and socio-sexual behavior, including “mounting (attempts)”, a strictly male behavior, which was not observed in control females. Aggression in a non-reproductive context did not appear to be sensitive to T supplementation. Our data indicate that in the budgerigar even marked sex differences in socio-sexual behavior may depend on the activational effects of T, while this is generally not the case in other species.