Song Quality Research Articles

Performance on tests of cognitive ability is not repeatable across years in a songbird

Studies of the cognitive abilities of animals aim to help us understand how they communicate, obtain resources, avoid danger and otherwise thrive in a given environment. But to what extent is cognitive ability a fixed trait in individuals? And can we answer this question by measuring performance on tests of cognitive ability? We tested the same 18 male song sparrows, Melospiza melodia, once yearly, across three consecutive years, with tests of four putative cognitive traits and a test of neophobia. We also tested 19 females twice, once in the first year and once in the third year. All birds were hand-reared and tested in the laboratory. Analyses of both data sets indicate repeatability of neophobia but not of performance on the cognitive tests. In addition, correlations among cognitive performance, neophobia and song quality that were observed in the first year were not observed in subsequent rounds of testing. These results suggest that cognitive ability is not a fixed trait in individuals, or that the tests used do not accurately measure cognitive ability, or both. Conclusions drawn from a single round of cognitive tests should therefore be interpreted with caution in this species and in any species in which repeatability has not been verified.

How does testosterone act to regulate a multifaceted adaptive response? Lessons from studies of the avian song system.

In male songbirds, song functions to attract a mate or to defend a territory; it is therefore often produced in the context of reproduction. Testosterone of gonadal origin increases during the reproductive phase of the annual cycle and significantly enhances song production, as well as song development, via effects on song crystallisation. The neural control of birdsong production and learning is highly modular. We implanted testosterone or androgen antagonists into specific brain regions or in the periphery of castrated male canaries and, in this way, identified how androgen signalling in specific locations regulates a variety of birdsong features. For example, castrated male canaries treated with testosterone in the preoptic area only and exposed to long days sing at high rates compared to castrated male canaries not treated with testosterone. However, these birds with testosterone in the preoptic area still produce songs with substantially lower song stereotypy and amplitude; these features are controlled by testosterone acting in the song control nuclei HVC and robust nucleus of the arcopallium. Specific aspects of the learned singing behaviour are thus regulated by androgens acting at multiple levels in the brain in a non-redundant fashion. The action of testosterone in the preoptic area is related to the hormonal regulation of the motivation to sing but not to various aspects of song performance. Multiple aspects of song quality are instead precisely regulated by steroids acting in distinct song control nuclei. Females exert a strong choice for specific features of male song in canaries and this choice is influenced by the endocrine state of the female. The female song system is also involved in song production, as well as song perception, although the specificity of this hormone action has not yet been investigated.

Effect of shell as natural testosterone boosters in Sprague Dawley rats.

Aim:This study aimed to evaluate the effect of shell supplementation on the regulation of male reproduction in ratsMaterials and Methods:The zinc (Zn) level of shell from blood clam (Anadara granosa), green mussel (Perna viridis), and conch shell (Telescopium telescopium) was analyzed. The highest Zn content shell was fed to male Sprague Dawley rats for 0, 9, 30, and 50 days at the dose of either 0.09 mg/200 g BW or 0.18 mg/200 g BW. To determine the testosterone levels, blood was collected through the infraorbitalis sinus just before the rat was sacrificed. Testicular and brain were also collected for Cyp19 aromatase receptor analysis.Results:The Zn level in the shell of blood clam, green mussel, and conch shell 61.55 mg/kg, 2.78 mg/kg, and 3.93 mg/kg, respectively. The testosterone level of T1 group receiving 0.18 mg/200 g BW for 0, 9, 30, and 50 days was 1.42±0.59, 2.15±1.58, 2.98±2.53, and 8.11±2.03 ng/mL, respectively. The testosterone level of T2 group receiving 0.09 mg/200 g BW for 0, 9, 30, and 50 days was 2.50±0.32, 1.25±0.60, 3.87±3.27, and 3.54±0.23 ng/mL, respectively. The T3 group receiving Na-CMC showed the level of testosterone at days 0, 9, 30, and 50 days was 0.77±0.22, 1.99±1.65, 4.12±0.07, and 2.19±1.30 ng/mL, respectively. Finally, the T4 group receiving Zn showed testosterone levels at days 0, 9, 30, and 50 days was 0.51±0.58, 2.24±3.16, 4.58±1.97, and 2.89±0.20 ng/mL, respectively. There was a significant difference (p<0.05) between the T1 group compared to the other groups. However, the absence of expression of Cyp19 aromatase both in Leydig cells and the brain indicated no conversion of testosterone to estradiol. To add, this finding showed the potential use of the shell to boost the testosterone level in male rats.Conclusion:Shell acted as an aromatase blocker to boost the testosterone level in male rats. This also indicates its promising application in birds to manipulate the quality of song and feather.

Full life course analysis of birdsong reveals maturation and senescence of highly repeatable song characteristics

AbstractSignalers may benefit in some contexts from advertising their ages, for example in courting potential mates. Receivers in turn may benefit from assessing a signaler’s age, even in cases where their doing so is against the signaler’s interests. Indicators of age contained in signals thus may have important fitness consequences for both signalers and receivers. In birds, males of many species have been shown to display delayed maturation of their songs, resulting in older males singing songs that are higher in quality in one or more characteristics. Conversely, it seems possible that songs might eventually deteriorate with age as an aspect behavioral senescence. Studies of birdsong long enough to test both possibilities are quite uncommon, with nearly all studies aspect of age-dependent changes in birdsong spanning 3 or fewer years of males’ lives. Here, we present the longest longitudinal analysis of male birdsong to date, in which we analyze songs recorded for 4–11 years of the lives of captive male swamp sparrows. We find that males displayed delayed maturation of three song characteristics: song rate, song length, and consistency between songs. Delayed maturation was followed by behavioral senescence of three characteristics: song rate, stereotypy within songs, and consistency between songs. Because song quality declined in males beyond 2 years of age, this evidence is inconsistent with a signaling system in which females both prefer increasingly older males and are able to accurately determine male age through song assessment. Rather, our evidence suggests that swamp sparrows should be able to use song to distinguish intermediate-aged males from 1-year-old and very old males.

Is male condition corrected with song features in Dusky Warblers (Phylloscopus fuscatus)

BackgroundBirdsong is an important form of communication that plays an important role in territorial defense and mate attraction by conveying valuable information. While body-size and song frequency are often negatively correlated among species, this relationship is only found in a few songbirds. Previous studies on the Dusky Warbler (Phylloscopus fuscatus) found that there was a positive correlation between tarsus length and peak frequency. And heavier male Dusky Warblers possess better territories and obtain more opportunities for mating; body condition may be related to reproduction of birds, so females may choose heavier mates or better body condition based on the singing characteristics of males.MethodsWe recorded spontaneous song and measured morphology of 33 male Dusky Warblers in Saihanba Forest Farm area between July 5 and August 10, 2015. We chose body weight as an indicator of body size and defined body condition as residuals from a linear regression between body weight and tarsus length. Frist, we used Pearson correlation to analyze whether date and time of day were correlated with weight, and then we used linear regression to analyze whether sound features could indicate the body weight and body condition. We call body weight and body condition the male condition.ResultsWe found no effect of date and time of day on weight, and we showed a correlation between the male condition and song features in the small songbird, Dusky Warbler. Maximum trill quality and maximum peak frequency of songs were negatively related to male condition; the mean number of syllables of songs and maximum high frequency of songs were positively correlated with body weight and body condition.ConclusionsIn the small songbird, Dusky Warbler, four song parameters, including maximum trill quality, mean number of syllables of songs, maximum peak frequency of songs, maximum high frequency of songs, significantly predicted male condition change of which the most important song characteristic for male condition was maximum trill quality. This study suggested that the extreme song features were more constrained by male condition than mean sound characteristics.

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 14days. 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.

Testosterone or Estradiol When Implanted in the Medial Preoptic Nucleus Trigger Short Low-Amplitude Songs in Female Canaries.

In male songbirds, the motivation to sing is largely regulated by testosterone (T) action in the medial preoptic area, whereas T acts on song control nuclei to modulate aspects of song quality. Stereotaxic implantation of T in the medial preoptic nucleus (POM) of castrated male canaries activates a high rate of singing activity, albeit with a longer latency than after systemic T treatment. Systemic T also increases the occurrence of male-like song in female canaries. We hypothesized that this effect is also mediated by T action in the POM. Females were stereotaxically implanted with either T or with 17β-estradiol (E2) targeted at the POM and their singing activity was recorded daily during 2 h for 28 d until brains were collected for histological analyses. Following identification of implant localizations, three groups of subjects were constituted that had either T or E2 implanted in the POM or had an implant that had missed the POM (Out). T and E2 in POM significantly increased the number of songs produced and the percentage of time spent singing as compared with the Out group. The songs produced were in general of a short duration and of poor quality. This effect was not associated with an increase in HVC volume as observed in males, but T in POM enhanced neurogenesis in HVC, as reflected by an increased density of doublecortin-immunoreactive (DCX-ir) multipolar neurons. These data indicate that, in female canaries, T acting in the POM plays a significant role in hormone-induced increases in the motivation to sing.

Rapid testosterone-induced growth of the medial preoptic nucleus in male canaries

Testosterone activates singing within days in castrated male songbirds but full song quality only develops after a few weeks. Lesions of the medial preoptic nucleus (POM) inhibit while stereotaxic testosterone implants into this nucleus increase singing rate suggesting that this site plays a key role in the regulation of singing motivation. Testosterone action in the song control system works in parallel to control song quality. Accordingly, systemic testosterone increases POM volume within 1–2 days in female canaries, while the increase in volume of song control nuclei takes at least 2 weeks. The current study tested whether testosterone action is associated with similar differences in latencies in males. Photosensitive castrated male canaries were implanted with testosterone-filled Silastic™ implants and control castrates received empty implants, while simultaneously the photoperiod was switched from short- to long-days. Brains were collected from all subjects two days later. Plasma testosterone was elevated in testosterone-treated but not in controls. HVC volumes were not affected, but testosterone significantly increased the POM volume as identified by the dense group of aromatase-immunoreactive neurons, the number and somal area of these neurons and the fractional area they cover in POM. Testosterone-treated females from a previous experiment had a smaller POM volume in similar conditions suggesting the existence of a stable sex difference potentially affecting singing behavior. Thus testosterone induces male POM growth and aromatase expression in this nucleus within two days without affecting HVC size, further supporting the notion that testosterone increases singing motivation via its action in POM.

The effect of early life conditions on song traits in male dippers (Cinclus cinclus).

Song complexity and singing frequency in male birds are shaped by female choice; they signal male quality because song is costly to develop and produce. The timing of song learning and the development of the brain structures involved occur during a period when chicks are exposed to a number of potential stressors. The quality and quantity of song produced by adults may therefore reflect the level of stress experienced during early life, a theory known as the ‘developmental stress hypothesis’. We tested this hypothesis using song recordings and life-history data from an individually marked, long-term study population of wild dippers (Cinclus cinclus). The extent to which early life conditions predict adult song traits was investigated using natal brood size as a measure of sibling competition; the rate of provisioning by parents as a proxy for nutritional stress; and residuals of the linear regression between body mass and tarsus length as a measure of nestling condition. The syllable diversity in the songs of adult males was positively correlated with their body condition as nestlings, but there was no significant correlation with either provisioning rate or brood size. Provisioning rate did, however, predict song rate; males in relatively poor condition as nestlings or those raised in smaller broods which were fed more frequently by their parents sang at a higher rate in adulthood. These results support the developmental stress hypothesis and provide some of the first evidence from a wild bird of how the conditions experienced during early life impact adult song. Song traits may therefore provide females with information regarding both the current condition and developmental history of males.

Singing activity‐driven Arc expression associated with vocal acoustic plasticity in juvenile songbird

Learned vocalization, including birdsong and human speech, is acquired through self‐motivated vocal practice during the sensitive period of vocal learning. The zebra finch (Taeniopygia guttata) develops a song characterized by vocal variability and crystallizes a defined song pattern as adulthood. However, it remains unknown how vocal variability is regulated with diurnal singing during the sensorimotor learning period. Here, we investigated the expression of activity‐dependent neuroplasticity‐related gene Arc during the early plastic song phase to examine its potential association with vocal plasticity. We first confirmed that multiple acoustic features of syllables in the plastic song were dramatically and simultaneously modulated during the first 3 hr of singing in a day and the altered features were maintained until sleep. In a concurrent manner, Arc was intensely induced during morning singing and a subsequent attenuation during afternoon singing in the robust nucleus of the arcopallium (RA) and the interfacial nucleus of the nidopallium (NIf). The singing‐driven Arc expression was not altered by circadian rhythm, but rather reduced during the day as juveniles produced more songs. Song stabilization accelerated by testosterone administration in juveniles was accompanied with attenuation of Arc induction in RA and NIf. In contrast, although early‐deafened birds produced highly unstable song even at adulthood, singing‐driven Arc expression was not different between intact and early‐deafened adults. These results suggest a potential functional link between Arc expression in RA and NIf and vocal plasticity during the sensorimotor phase of song learning. Nonetheless, Arc expression did not reflect the quality of bird's own song or auditory feedback.

Behavioral evidence for sex steroids hypersensitivity in castrated male canaries

In seasonally breeding songbirds such as canaries, singing behavior is predominantly under the control of testosterone and its metabolites. Short daylengths in the fall that break photorefractoriness are followed by increasing daylengths in spring that activate singing via both photoperiodic and hormonal mechanisms. However, we observed in a group of castrated male Fife fancy canaries maintained for a long duration under a short day photoperiod a large proportion of subjects that sang at high rates. This singing rate was not correlated with variation in the low circulating concentrations of testosterone. Treatment of these actively singing castrated male canaries with a combination of an aromatase inhibitor (ATD) and an androgen receptor blocker (flutamide) only marginally decreased this singing activity as compared to control untreated birds and did not affect various measures of song quality. The volumes of HVC and of the medial preoptic nucleus (POM) were also unaffected by these treatments but were relatively large and similar to volumes in testosterone-treated males. In contrast, peripheral androgen-sensitive structures such as the cloacal protuberance and syrinx mass were small, similar to what is observed in castrates. Together these data suggest that after a long-term steroid deprivation singing behavior can be activated by very low concentrations of testosterone. Singing normally depends on the activation by testosterone and its metabolites of multiple downstream neurochemical systems such as catecholamines, nonapeptides or opioids. These transmitter systems might become hypersensitive to steroid action after long term castration as they probably are at the end of winter during the annual cycle in seasonally breeding temperate zone species.

Bidirectional scaling of vocal variability by an avian cortico-basal ganglia circuit.

Behavioral variability is thought to be critical for trial and error learning, but where such motor exploration is generated in the central nervous system is unclear. The zebra finch songbird species offers a highly appropriate model in which to address this question. The male song is amenable to detailed measurements of variability, while the brain contains an identified cortico‐basal ganglia loop that underlies this behavior. We used pharmacogenetic interventions to separately interrogate cortical and basal ganglia nodes of zebra finch song control circuitry. We show that bidirectional manipulations of each node produce near mirror image changes in vocal control: Cortical activity promotes song variability, whereas basal ganglia activity promotes song stability. Furthermore, female conspecifics can detect these pharmacogenetically elicited changes in song quality. Our results indicate that cortex and striatopallidum can jointly and reciprocally affect behaviorally relevant levels of vocal variability, and point to endogenous mechanisms for its control.

Song is not a reliable signal of general cognitive ability in a songbird

Learned aspects of song affect female mating preferences in a number of species of songbirds, including swamp sparrows, Melospiza georgiana. One explanation for why female songbirds attend to such song features is that these song attributes convey information on the general cognitive ability of singers. The fact that song attributes and cognitive ability are affected during development by the same stressors makes a connection between the two plausible. Here we test the hypothesis that song is a signal of cognitive ability by relating five measures of song quality to five measures of cognitive performance in 49 captive male swamp sparrows. The five song measures are repertoire size, mean and minimum vocal deviation (measures of vocal performance), and mean and maximum typicality (measures of song learning). Cognitive performance was measured as the speed with which five cognitive tasks were mastered: a novel foraging task, a colour association, a colour reversal, a spatial learning problem and a detour-reaching test. In general linear mixed models controlling for neophobia, none of the song measures were predictive of any of the cognitive performance measures. Thus the results do not support the hypothesis that song attributes signal general cognition in swamp sparrows.

Negative impact of urban noise on sexual receptivity and clutch size in female domestic canaries

AbstractIn oscines, male song stimulates female reproduction and females are known to adjust both their sexual preferences and their maternal investment according to song quality. Female domestic canaries are especially responsive to wide frequency bandwidth (4 kHz) male songs emitted with a high‐repetition syllable rate and low minimal frequencies (1 kHz). We previously showed that low‐frequency urban noise decreases female sexual responsiveness for these low‐frequency songs (1–5 kHz) through auditory masking. Based on the differential allocation hypothesis, we predicted that urban noise exposure will equally affect female maternal investment. Using a crossover design, we broadcast low‐frequency songs to females either in an overlapping noise condition or in an alternating noise condition. Females decreased both their sexual responsiveness and their clutch size in the overlapping noise treatment relative to the alternative noise treatment. No differences were found concerning egg size or egg composition (yolk and albumen mass, testosterone concentration). Due to our experimental design, we can exclude a general impact of noisy conditions and thereby provide evidence for a detrimental effect through masking on avian courtship and reproductive output. These results suggest that noisy conditions may also affect avian communication in outdoor conditions, which may partly explain field reports on noise‐dependent breeding success and reduced breeding densities at noisy sites.

Flightin maintains myofilament lattice organization required for optimal flight power and courtship song quality in Drosophila.

The indirect flight muscles (IFMs) of Drosophila and other insects with asynchronous flight muscles are characterized by a crystalline myofilament lattice structure. The high-order lattice regularity is considered an adaptation for enhanced power output, but supporting evidence for this claim is lacking. We show that IFMs from transgenic flies expressing flightin with a deletion of its poorly conserved N-terminal domain (flnΔN62 ) have reduced inter-thick filament spacing and a less regular lattice. This resulted in a decrease in flight ability by 33% and in skinned fibre oscillatory power output by 57%, but had no effect on wingbeat frequency or frequency of maximum power output, suggesting that the underlying actomyosin kinetics is not affected and that the flight impairment arises from deficits in force transmission. Moreover, we show that flnΔN62 males produced an abnormal courtship song characterized by a higher sine song frequency and a pulse song with longer pulses and longer inter-pulse intervals (IPIs), the latter implicated in male reproductive success. When presented with a choice, wild-type females chose control males over mutant males in 92% of the competition events. These results demonstrate that flightin N-terminal domain is required for optimal myofilament lattice regularity and IFM activity, enabling powered flight and courtship song production. As the courtship song is subject to female choice, we propose that the low amino acid sequence conservation of the N-terminal domain reflects its role in fine-tuning species-specific courtship songs.

Quantity and quality of available mates alters female responsiveness but not investment in the Pacific field cricket, Teleogryllus oceanicus

An individuals’ experience with conspecific signaling during development can lead to variation in their mating signals and behavior later in life. It is unclear whether experience with sexual signals also alters receivers’ fitness through changes in investment in offspring. Male field crickets attract mates using a long-distance calling song. To determine how developmental experience with calling song quality and quantity alters mating responsiveness and fitness, we raised juvenile female Teleogryllus oceanicus in five acoustic environments. These environments mimicked two mate quantities (high and low) crossed with two mate qualities (high and low), and a silent control. At adulthood, we measured females’ responsiveness in phonotaxis trials. Following phonotaxis, females were offered opportunities to mate and lay eggs. We measured egg number and proportion hatching as components of fitness and reproductive investment. Corroborating previous research in this system, female crickets raised in silence approached a broadcast calling song nearly 45% faster than their counterparts reared hearing a high-quantity/high-quality combination of calling song. Additionally, females adjusted other aspects of phonotaxis behavior in response to the quantity, but not quality of song. We found no evidence that females adjusted mating rates or investment in offspring. Regardless of acoustic experience, females laid equivalent numbers of eggs that had equivalent hatching success. Our results show that female mating behavior responds to juvenile experience mimicking a lack of mating opportunities, but is less responsive to variation in mate quality. Furthermore, reproductive investment may be less plastic than mating behavior. Social experience can inform organisms about current environmental conditions and lead to changes in behavior. Existing work suggests that field crickets in the genus Teleogryllus change their mating behavior in response to acoustic environments that mimic varied mate availabilities and qualities. However, we do not know if females alter their investment in offspring under similar circumstances. Variable investment could speed evolutionary change when combined with behavioral plasticity. We found that although female mating behavior is sensitive to variation in acoustic experience, reproductive investment is not. The number of eggs laid and the percent hatching did not depend on acoustic experience. We discuss evolutionary explanations for these patterns, including the possibility that investment is less plastic than mating behavior.

Experimentally increased prebreeding male social behaviour has no effect on female breeding phenology and performance

In the context of breeding phenology, social behaviour (especially song) has long been considered an important ‘supplemental cue’ that females integrate with other environmental information to determine timing of egg laying. However, to our knowledge, no studies have experimentally manipulated song in the wild in the context of female breeding phenology and performance. We studied natural variation in, and response to experimental manipulation of, prebreeding song and social behaviour in European starlings, Sturnus vulgaris, to determine whether male behaviour acts as a phenological cue determining female timing of egg laying and subsequent, postlaying breeding performance. In our highly synchronous system, natural variation in prebreeding male song quality and singing effort was surprisingly high, and singing increased slightly closer to egg-laying date. There was a strong prebreeding response of both males and females to the playback treatment, but no effect on female breeding phenology (egg-laying date) or performance (nestbox occupancy, egg size, clutch size, total chicks hatched, total chicks fledged or double-brooding behaviour). Our 3-year study finds no evidence that male prebreeding song is a cue determining female breeding phenology or performance in starlings.

Understanding consumer preferences and demography in order to reduce the domestic trade in wild-caught birds

The wildlife trade is now one of the greatest threats to biodiversity, and birds are among the most commonly traded groups worldwide. The demand for pet birds is especially high in Indonesia, a country with many exploited, imperiled bird species. Finding solutions to the threat that trade poses for birds, and wildlife in general, requires an understanding of its socioeconomic dimensions. We examined consumer demography and preferences of 762 bird owners in Medan, Sumatra, focusing on the differences among owners of birds taken from the wild versus birds bred in captivity. We found that the vast majority of bird owners have at least one wild-caught bird. However, wild-caught bird ownership is not uniformly distributed across Medan; rather, there are distinct hotspots with high proportions of people with wild-caught birds. The main reasons for owning wild-caught birds are lack of access to and the high cost of captive-bred birds, and a perception that captive-bred birds do not sing as well as wild-caught ones. We conclude that captive-breeding programs could reduce the pressure on wild populations, especially if suppliers are able to produce relatively cheap captive-bred birds. However, the perceived poorer song quality of captive-bred individuals might be a problem for the captive breeding of some species, notably the White-rumped Shama, Copsychus malabaricus. Since many owners of this species compete in bird song competitions, establishing competition categories specifically for captive-bred shamas could promote captive-bred bird ownership. Tackling the problem of the wild bird trade in Indonesia and elsewhere will require consideration of both the economic and the social factors that underlie pet ownership.

Testosterone-induced neuroendocrine changes in the medial preoptic area precede song activation and plasticity in song control nuclei of female canaries.

Testosterone plays a key role in the control of seasonal changes in singing behavior and its underlying neural circuitry. After administration of exogenous testosterone, song quality and song control nuclei volumes change over the course of weeks, but song rate increases within days. The medial preoptic nucleus (POM) controls sexual motivation and testosterone action in POM increases sexually motivated singing. In this study, we investigated the time course of testosterone action in the song control nuclei and POM, at the gross anatomical and cellular level. Photosensitive female canaries were injected with BrdU to label newborn neurons. One day later they were transferred to a long-day photoperiod and implanted with testosterone-filled or empty implants. Brains and blood were collected 1, 2, 9 or 21days later. Testosterone increased POM volume within 1day, whereas the volume of song control nuclei increased significantly only on day 21 even if a trend was already observed for HVC on day 9. The density of newborn neurons in HVC, labeled by Bromodeoxyuridine (BrdU) and doublecortin, was increased by testosterone on days 9 and 21 although a trend was already detectable on day 2. In POM, testosterone increased the number and size of aromatase-immunoreactive neurons already after 1day. This rapid action of testosterone in POM supports its proposed role in controlling singing motivation. Although testosterone increased the number of newborn neurons in HVC rapidly (9, possibly 2days), it is unlikely that these new neurons affect singing behavior before they mature and integrate into functional circuits.

Hatching asynchrony impacts cognition in male zebra finches

Conditions experienced early in life can shape brain development and later cognition. Altricial songbirds are particularly vulnerable to early environmental perturbations. Research on "Developmental Stress" in songbirds has addressed how early-life conditions may impair song learning and has been extended to consider other components of adult phenotype. Early-life challenges ranging from ectoparasites to competition with siblings have been shown to compromise song learning and other measures of cognition, as well as behavioral strategy. Here, we examined both the effects of hatching asynchrony and early-life immune system challenge with lipopolysaccharide (LPS) on neophobia, song learning, motoric learning, and spatial cognition in male zebra finches (Taeniopygia guttata). We found that hatch order had a significant impact on motoric and spatial learning, such that later hatched males performed better than first and second hatched birds. In contrast, LPS treatment only impacted motoric learning and neither hatch order nor immune system challenge impacted song quality, song learning accuracy, or neophobia. These results are consistent with a growing body of evidence that conditions early in life can improve cognitive performance at adulthood. Moreover, these findings indicate that hatch order is an important factor to consider in developmental studies in asynchronously hatching birds.