Developmental stress impairs song complexity but not learning accuracy in non-domesticated zebra finches (Taeniopygia guttata)

Experimental biology can inform our understanding of food insecurity

Food insecurity is a major public health issue. Millions of households worldwide have intermittent and unpredictable access to food and this experience is associated with greater risk for a host of negative health outcomes. While food insecurity is a contemporary concern, we can understand its effects better if we acknowledge that there are ancient biological programs that evolved to respond to the experience of food scarcity and uncertainty, and they may be particularly sensitive to food insecurity during development. Support for this conjecture comes from common findings in several recent animal studies that have modeled insecurity by manipulating predictability of food access in various ways. Using different experimental paradigms in different species, these studies have shown that experience of insecure access to food can lead to changes in weight, motivation and cognition. Some of these studies account for changes in weight through changes in metabolism, while others observe increases in feeding and motivation to work for food. It has been proposed that weight gain is an adaptive response to the experience of food insecurity as 'insurance' in an uncertain future, while changes in motivation and cognition may reflect strategic adjustments in foraging behavior. Animal studies also offer the opportunity to make in-depth controlled studies of mechanisms and behavior. So far, there is evidence that the experience of food insecurity can impact metabolic efficiency, reproductive capacity and dopamine neuron synapses. Further work on behavior, the central and peripheral nervous system, the gut and liver, along with variation in age of exposure, will be needed to better understand the full body impacts of food insecurity at different stages of development.

Variable ambient temperature promotes song learning and production in zebra finches

Current climate change is leading to increasingly unpredictable environmental conditions and is imposing new challenges to wildlife. For example, ambient conditions fluctuating during critical developmental periods could potentially impair the development of cognitive systems and may therefore have a long-term influence on an individual's life. We studied the impact of temperature variability on zebra finch cognition, focusing on song learning and song quality (N = 76 males). We used a 2 × 2 factorial experiment with two temperature conditions (stable and variable). Half of the juveniles were cross-fostered at hatching to create a mismatch between pre- and posthatching conditions, the latter matching this species' critical period for song learning. We found that temperature variability did not affect repertoire size, syllable consistency, or the proportion of syllables copied from a tutor. However, birds that experienced variable temperatures in their posthatching environment were more likely to sing during recordings. In addition, birds that experienced variable prenatal conditions had higher learning accuracy than birds in stable prenatal environments. These findings are the first documented evidence that variable ambient temperatures can influence song learning in zebra finches. Moreover, they indicate that temperature variability can act as a form of environmental enrichment with net positive effects on cognition.

Mitochondria as the powerhouses of sexual selection: Testing mechanistic links between development, cellular respiration, and bird song

The developmental environment can affect the expression of sexually selected traits in adulthood. The physiological mechanisms that modulate such effects remain a matter of intense debate. Here, we test the role of the developmental environment in shaping adult mitochondrial function and link mitochondrial function to expression of a sexually selected trait in males (bird song). We exposed male zebra finches (Taeniopygia guttata) to corticosterone (CORT) treatment during development. After males reached adulthood, we quantified mitochondrial function from whole red blood cells and measured baseline CORT and testosterone levels, body condition/composition, and song structure. CORT-treated males had mitochondria that were less efficient (FCR_L/R) and used a lower proportion of maximum capacity (FCR_R/ETS) than control males. Additionally, CORT-treated males had higher baseline levels of CORT as adults compared to control males. Using structural equation modelling, we found that the effects of CORT treatment during development on adult mitochondrial function were indirect and modulated by baseline CORT levels, which are programmed by CORT treatment during development. Developmental treatment also had an indirect effect on song peak frequency. Males treated with CORT during development sang songs with higher peak frequency than control males, but this effect was modulated through increased CORT levels and by a decrease in FCR_R/ETS. CORT-treated males had smaller tarsi compared to control males; however, there were no associations between body size and measures of song frequency. Here, we provide the first evidence supporting links between the developmental environment, mitochondrial function, and the expression of a sexually selected trait (bird song).

Detrimental or beneficial? Untangling the literature on developmental stress studies in birds

Developing animals display a tremendous ability to change the course of their developmental path in response to the environment they experience, a concept referred to as developmental plasticity. This change in behavior, physiology or cellular processes is primarily thought to allow animals to better accommodate themselves to the surrounding environment. However, existing data on developmental stress and whether it brings about beneficial or detrimental outcomes show conflicting results. There are several well-referred hypotheses related to developmental stress in the current literature, such as the environmental matching, silver spoon and thrifty phenotype hypotheses. These hypotheses speculate that the early-life environment defines the capacity of the physiological functions and behavioral tendencies and that this change is permanent and impacts the fitness of the individual. These hypotheses also postulate there is a trade-off among organ systems and physiological functions when resources are insufficient. Published data on avian taxa show that some effects of developmental nutritional and thermal stressors are long lasting, such as the effects on body mass and birdsong. Although hypotheses on developmental stress are based on fitness components, data on reproduction and survival are scarce, making it difficult to determine which hypothesis these data support. Furthermore, most physiological and performance measures are collected only once; thus, the physiological mechanisms remain undertested. Here, we offer potential avenues of research to identify reasons behind the contrasting results in developmental stress research and possible ways to determine whether developmental programming due to stressors is beneficial or detrimental, including quantifying reproduction and survival in multiple environments, measuring temporal changes in physiological variables and testing for stress resistance later in life.

Humpback whale song recordings suggest common feeding ground occupation by multiple populations

Humpback whale males are known to sing on their low-latitude breeding grounds, but it is well established that songs are also commonly produced ‘off-season’ on the feeding grounds or during migration. This opens exciting opportunities to investigate migratory aggregations, study humpback whale behavioral plasticity and potentially even assign individual singers to specific breeding grounds. In this study, we analyzed passive acoustic data from 13 recording positions and multiple years (2011–2018) within the Atlantic sector of the Southern Ocean (ASSO). Humpback whale song was detected at nine recording positions in five years. Most songs were recorded in May, austral fall, coinciding with the rapid increase in sea ice concentration at most recording positions. The spatio-temporal pattern in humpback whale singing activity on Southern Ocean feeding grounds is most likely shaped by local prey availability and humpback whale migratory strategies. Furthermore, the comparative analyses of song structures clearly show a differentiation of two song groups, of which one was solely recorded at the western edge of the ASSO and the other song group was recorded throughout the ASSO. This new finding suggests a common feeding ground occupation by multiple humpback whale populations in the ASSO, allowing for cultural and potentially even genetic exchange among populations.

Like Father Like Son: Cultural and Genetic Contributions to Song Inheritance in an Estrildid Finch

Social learning of vocalizations is integral to song inheritance in oscine passerines. However, other factors, such as genetic inheritance and the developmental environment, can also influence song phenotype. The relative contributions of these factors can have a strong influence on song evolution and may affect important evolutionary processes such as speciation. However, relative contributions are well-described only for a few species and are likely to vary with taxonomy. Using archived song data, we examined patterns of song inheritance in a domestic population of Java sparrows (Lonchura oryzivora), some of which had been cross-fostered. Six-hundred and seventy-six songs from 73 birds were segmented and classified into notes and note subtypes (N = 22,972), for which a range of acoustic features were measured. Overall, we found strong evidence for cultural inheritance of song structure and of the acoustic characteristics of notes; sons’ song syntax and note composition were similar to that of their social fathers and were not influenced by genetic relatedness. For vocal consistency of note subtypes, a measure of vocal performance, there was no apparent evidence of social or genetic inheritance, but both age and developmental environment influenced consistency. These findings suggest that high learning fidelity of song material, i.e., song structure and note characteristics, could allow novel variants to be preserved and accumulate over generations, with implications for evolution and conservation. However, differences in vocal performance do not show strong links to cultural inheritance, instead potentially serving as condition dependent signals.

Chronic exposure to urban noise during the vocal learning period does not lead to increased song frequencies in zebra finches

Abstract

It has often been observed that birds sing at a higher pitch in cities and other areas that are polluted with intense low-frequency noise. How this pattern arises remains unclear though. One prevailing idea is that songbirds adjust song frequencies to environmental noise profiles through developmental plasticity via vocal learning. However, the conclusions of previous studies testing this hypothesis are inconsistent. Here we report the findings from two song learning experiments with zebra finches (Taenopygia guttata), in which we exposed young birds to anthropogenic noise during their sensitive vocal learning period. Unlike previous studies that addressed this issue, we did not use constant synthetic noise but natural urban noise with its typical amplitude fluctuations that was broadcast at realistic sound levels. We found that noise-exposed males in neither experiment developed higher pitched songs compared to control males. This suggests that the natural fluctuations between higher and lower noise levels in cities may allow young birds to exploit relatively quiet moments to hear their tutors and themselves, permitting them to make accurate copies of even low-frequency song elements.

Significance statement

If animals are to persist in urban habitats, they often must adjust their behavior to the altered conditions. Birds in cities are often observed to sing at a higher pitch, but we are largely ignorant of how this phenomenon arises. We investigated whether low-frequency traffic noise interferes with the song learning of birds so that they develop higher pitched songs. Accordingly, we played back natural traffic noise from urban bird habitats to young birds during their learning period and then analyzed their adult songs. We found that birds that learned their songs in noise did not sing at higher frequencies compared to control males that learned their song with no noise exposure. Our results show that typical traffic noise in cities may not be sufficient to interfere with vocal learning in a way that birds develop higher-pitched songs.

Learning strategies and the social brain: Missing elements in the link between developmental stress, song and cognition?

Bird songs may advertise aspects of cognition because song learning and learning speed in cognitive tasks are both affected by early-life environments. However, such relationships remain ambiguous in the literature. Here, I discuss 2 lines of research that may help to demystify links between song learning and cognition. First, learning strategies should be considered when assessing performance to ensure that individual differences in learning ability are not masked by individual differences in learning strategies. Second, song characteristics should be associated with social behavior because songs have a social purpose and, consequently, should be strongly related at functional and neural levels. Finally, if song learning and cognitive abilities are correlated because they develop concurrently and/or share or compete for the same resources, I discuss ways glucocorticoids may link early-life stress, song learning and cognitive ability, focusing particularly on oxidative stress as a potential mechanism.

Stress hormones, social associations and song learning in zebra finches

The use of information provided by others is a common short-cut adopted to inform decision-making. However, instead of indiscriminately copying others, animals are often selective in what, when and whom they copy. How do they decide which 'social learning strategy' to use? Previous research indicates that stress hormone exposure in early life may be important: while juvenile zebra finches copied their parents' behaviour when solving novel foraging tasks, those exposed to elevated levels of corticosterone (CORT) during development copied only unrelated adults. Here, we tested whether this switch in social learning strategy generalizes to vocal learning. In zebra finches, juvenile males often copy their father's song; would CORT-treated juveniles in free-flying aviaries switch to copying songs of other males? We found that CORT-treated juveniles copied their father's song less accurately as compared to control juveniles. We hypothesized that this could be due to having weaker social foraging associations with their fathers, and found that sons that spent less time foraging with their fathers produced less similar songs. Our findings are in line with a novel hypothesis linking early-life stress and social learning: early-life CORT exposure may affect social learning indirectly as a result of the way it shapes social affiliations.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.

Early life conditions that impact song learning in male zebra finches also impact neural and behavioral responses to song in females

Early life stressors can impair song in songbirds by negatively impacting brain development and subsequent learning. Even in species in which only males sing, early life stressors might also impact female behavior and its underlying neural mechanisms, but fewer studies have examined this possibility. We manipulated brood size in zebra finches to simultaneously examine the effects of developmental stress on male song learning and female behavioral and neural response to song. Although adult male HVC volume was unaffected, we found that males from larger broods imitated tutor song less accurately. In females, early condition did not affect the direction of song preference: all females preferred tutor song over unfamiliar song in an operant test. However, treatment did affect the magnitude of behavioral response to song: females from larger broods responded less during song preference trials. This difference in activity level did not reflect boldness per se, as a separate measure of this trait did not differ with brood size. Additionally, in females we found a treatment effect on expression of the immediate early gene ZENK in response to tutor song in brain regions involved in song perception (dNCM) and social motivation (LSc.vl, BSTm, TnA), but not in a region implicated in song memory (CMM). These results are consistent with the hypothesis that developmental stressors that impair song learning in male zebra finches also influence perceptual and/or motivational processes in females. However, our results suggest that the learning of tutor song by females is robust to disturbance by developmental stress. © 2018 Wiley Periodicals, Inc. Develop Neurobiol, 2018.

Mate choice decision rules: Trait synergisms and preference shifts

An important and understudied question in sexual selection is how females evaluate information from multiple secondary sexual traits (SSTs), particularly when expression of traits is phenotypically uncorrelated. We performed mate choice experiments on zebra finches (Taeniopygia guttata castanotis Gould) to evaluate two hypotheses: preference shifts (obstacles to choice using one trait increase chooser reliance on others) and trait synergisms (choice based on the sum/product of two or more independently varying traits). The first experiment, which employed males raised on diets that impact SST expression, supported the trait synergism hypothesis: overall, male pairing success was best predicted by synergisms involving beak color and cheek patch size. Results did not support the preference shift hypothesis. Results of a follow-up experiment that included males reared on a single diet, and in which male beak color and cheek patch size were manipulated, were also consistent with the trait synergism hypothesis. Results have implications for understanding the long-term persistence of multiple SSTs in populations and for the measurement of repeatability and heritability of mate preferences.

Early life stress increases testosterone and corticosterone and alters stress physiology in zebra finches

Early life stress has enduring effects on behavior and physiology. However, the effects on hormones and stress physiology remain poorly understood. In the present study, parents of zebra finches of both sexes were exposed to an increased foraging paradigm from 3 to 33days post hatching. Plasma and brains were collected from chicks at 3 developmental time points: post hatching days 25, 60 and adulthood. Plasma was assayed for testosterone (T), estradiol (E2), and corticosterone (CORT). The paraventricular nucleus of the hypothalamus was assessed for corticotrophin releasing factor (CRH) and glucocorticoid receptor (GR) expression. As expected, body mass was lower in nutritionally stressed animals compared to controls at multiple ages. Nutritionally stressed animals overall had higher levels of CORT than did control and this was particularly apparent in females at post hatching day 25. Nutritionally stressed animals also had a higher number of cells expressing CRH and GR in the paraventricular nucleus of the hypothalamus than did controls. There was an interaction, such that both measures were higher in control animals at PHD 25, but higher in NS animals by adulthood. Females, regardless of treatment, had higher circulating CORT and a higher number of cells expressing CRH than did males. Nutritionally stressed animals also had higher levels of T than did control animals, and this difference was greatest for males at post hatching day 60. There were no effects of nutritional stress on E2. These findings suggest that nutritional stress during development has long-lasting effects on testosterone and stress physiology.

Experimental exposure to urban and pink noise affects brain development and song learning in zebra finches (Taenopygia guttata)

Recently, numerous studies have observed changes in bird vocalizations-especially song-in urban habitats. These changes are often interpreted as adaptive, since they increase the active space of the signal in its environment. However, the proximate mechanisms driving cross-generational changes in song are still unknown. We performed a captive experiment to identify whether noise experienced during development affects song learning and the development of song-control brain regions. Zebra finches (Taeniopygia guttata) were bred while exposed, or not exposed, to recorded traffic urban noise (Study 1) or pink noise (Study 2). We recorded the songs of male offspring and compared these to fathers' songs. We also measured baseline corticosterone and measured the size of song-control brain regions when the males reached adulthood (Study 1 only). While male zebra finches tended to copy syllables accurately from tutors regardless of noise environment, syntax (the ordering of syllables within songs) was incorrectly copied affected by juveniles exposed to noise. Noise did not affect baseline corticosterone, but did affect the size of brain regions associated with song learning: these regions were smaller in males that had been had been exposed to recorded traffic urban noise in early development. These findings provide a possible mechanism by which noise affects behaviour, leading to potential population differences between wild animals occupying noisier urban environments compared with those in quieter habitats.

Effects of early-developmental stress on growth rates, body composition and developmental plasticity of the HPG-axis

In altricial songbirds, food restriction in early development has adverse effects on various physiological systems. When conditions improve birds can accelerate growth, but this compensatory strategy is associated with long-term adverse consequences. One system affected by altered growth rates is the hypothalamic-pituitary-gonadal (HPG) axis. Here, we subjected European starlings, Sturnus vulgaris, to an unpredictable food manipulation from 35 to 115days of age. We assessed the effects of the treatment by measuring overall body mass and body composition during and following the treatment period (i.e., accelerated growth). In adulthood, we measured the long-term effects of the treatment on overall body mass, testis volume, and HPG axis function in both sexes by quantifying androgen levels before and after a gonadotropin-releasing hormone (GnRH) challenge. During the treatment period, treatment birds had less body fat than controls. Following the treatment period, treatment birds weighed more than controls, but these gains were attributed to changes in lean mass. In adulthood, treatment males had lower baseline androgen levels, but there was no difference in peak androgen levels compared to controls. Treatment females did not differ from controls on any of the androgen measures. However, females that accelerated growth faster following the termination of the treatment had lower integrated androgen levels. When faced with limited developmental resources, birds may alter the developmental trajectory of physiological systems as a compensatory strategy. Such a strategy may have long-term consequences on endocrine regulation that could affect courtship and reproductive behaviors.

Song repertoire size, not territory location, predicts reproductive success and territory tenure in a migratory songbird

In territorial animals occupying environments that vary in quality over the landscape, high-quality individuals are predicted to monopolize high-quality territories. Thus, in many cases it may be difficult to disentangle the relative effects of individual quality from those of territory quality on long-term fitness. We used a 9-year field data set from a migratory population of Eastern Song Sparrows (Melospiza melodia melodia (A. Wilson, 1810)) to evaluate the relative contributions of male song quality (as measured by song repertoire size) and territory location to fitness components including annual reproductive success, overwinter return rates, and between-year territory tenure. Song repertoire size did not predict territory location, allowing us to evaluate territory location and song quality separately. Song repertoire size, but not territory location, predicted annual reproductive success. Moreover, males with larger repertoires moved smaller distances between subsequent breeding seasons, suggesting more successful territory tenure. There was no effect of either repertoire size or territory location on overwinter return. We conclude that intrinsic male phenotype, indicated by song repertoire size, is an important predictor of male fitness, independent of breeding-territory location in this migratory population, and that the value of specific territories may depend largely on previous experience.

No Trade-Offs between Lipid Stores and Structural Growth in Juvenile Zebra Finches Undergoing Nutritional Stress during Development

Nutritional conditions during development can affect both structural growth and body fat deposition. Body size and body fat each have significant consequences for fitness, yet few studies have investigated how young birds balance resource allocation between structural growth and fat reserves. We raised zebra finches (Taeniopygia guttata) in consistently high- or low-food conditions until posthatch day 35 (PHD 35). From this age until PHD 62, half of the birds in each condition were switched to the other treatment, while the rest were maintained on the same conditions. Body mass, lean mass, body fat, and tarsus length were measured before (PHD 25) and after (PHD 55) nutritional independence. Precise measures of body composition were obtained noninvasively at both ages using quantitative magnetic resonance analysis. At PHD 25, birds in the high treatment had more body mass and lean mass than birds in the low treatment, but nutritional treatments did not affect body fat at this age. Unexpectedly, the strategic response of birds that experienced deteriorating food availability was to maintain body mass by increasing body fat and decreasing lean mass. Birds that experienced an improvement in food availability significantly increased body mass by increasing lean mass and not body fat. Birds maintained on a low diet throughout did not significantly increase body mass, lean mass, or body fat. Tarsus length was not affected by nutritional manipulations. These findings indicate that nutritional stress did not affect the relationship between skeletal growth and body fat deposition because lean mass, body fat, and tarsus length can be independently regulated at different developmental periods depending on nutritional conditions.

Effects of nutritional stress during different developmental periods on song and the hypothalamic-pituitary-adrenal axis in zebra finches

In songbirds, developmental stress affects song learning and production. Altered hypothalamic-pituitary-adrenal (HPA) axis function resulting in elevated corticosterone (CORT) may contribute to this effect. We examined whether developmental conditions affected the association between adult song and HPA axis function, and whether nutritional stress before and after nutritional independence has distinct effects on song learning and/or vocal performance. Zebra finches (Taeniopygia guttata) were raised in consistently high (HH) or low (LL) food conditions until post-hatch day (PHD) 62, or were switched from high to low conditions (HL) or vice versa (LH) at PHD 34. Song was recorded in adulthood. We assessed the response of CORT to handling during development and to dexamethasone (DEX) and adrenocorticotropic hormone (ACTH) challenges during adulthood. Song learning and vocal performance were not affected by nutritional stress at either developmental stage. Nutritional stress elevated baseline CORT during development. Nutritional stress also increased rate of CORT secretion in birds that experienced stress only in the juvenile phase (HL group). Birds in the LL group had lower CORT levels after injection of ACTH compared to the other groups, however there was no effect of nutritional stress on the response to DEX. Thus, our findings indicate that developmental stress can affect HPA function without concurrently affecting song.

Effects of housing condition and early corticosterone treatment on learned features of song in adult male zebra finches

Early developmental stress can have long-term physiological and behavioral effects on an animal. Developmental stress and early corticosterone (Cort) exposure affect song quality in many songbirds. Early housing condition can act as a stressor and affect the growth of nestlings and adult song, and improvements in housing condition can reverse adverse effects of early stress exposure in rodents. However, little is known about this effect in songbirds. Therefore, we took a novel approach to investigate if housing condition can modify the effects of early Cort exposure on adult song in male zebra finches. We manipulated early housing conditions to include breeding in large communal flight cages (FC; standard housing condition; with mixed-sex and mix-aged birds) versus individual breeding cages (IBC, one male-female pair with small, IBC-S, or large clutches, IBC-L) in post-hatch Cort treated male birds. We found that Cort treated birds from IBC-S have higher overall song learning scores (between tutor and pupil) than from FC but there is no difference between these groups in the No-Cort treated birds. When examining the effects of Cort within each housing condition, overall song learning scores decreased in Cort treated birds from flight cages but increased in birds from IBC-S compared to controls. Likewise, the total number of syllables and syllable types increased significantly in Cort treated birds from IBC-S, but decreased in FC-reared birds though this effect was not statistically significant. These findings suggest that the effects of early Cort treatment on learned features of song depend on housing condition.

Juvenile nutritional stress affects growth rate, adult organ mass, and innate immune function in zebra finches (Taeniopygia guttata)

Developmental conditions may influence many aspects of adult phenotype, including growth and immune function. Whether poor developmental environments impair both growth and immune function or induce a trade-off between the two processes is inconclusive, and the impact of the timing of stress in determining this relationship has so far been overlooked. We tested the hypothesis that the long-term effects of nutritional stress on growth, body composition, and immune function in zebra finches (Taeniopygia guttata) are different depending on whether stress is experienced during an early or a juvenile phase (i.e., before or after nutritional independence, respectively). We raised birds on high (H) or low (L) food conditions until posthatch day (PHD) 35 and switched treatments for half of the birds in each of the H and L groups from PHD 36 to 61. We found that unfavorable juvenile conditions (PHD 36-61) increased somatic growth rates and liver mass, body fat, and some aspects of immune function. We also observed a positive relationship between growth and immune function, as individuals that grew faster as juveniles also had better innate immune responses as adults. There was no effect of treatment on basal metabolic rate. These findings demonstrate the importance of juvenile developmental conditions in shaping multiple aspects of the adult phenotype.

Habitat quality affects early physiology and subsequent neuromotor development of juvenile black-capped chickadees

In songbirds, the ability to learn and render the species-specific song is influenced by the development of both the song nuclei in the brain and the syrinx (bird's vocal apparatus) early in the bird's life. In black-capped chickadees (Poecille atricapillus), habitat quality is known to affect song structure, with birds in high-quality habitat (mature forest) having a higher song consistency than birds in low-quality habitat (young forest). Although this difference is suspected to stem from differences in development, the developmental status of juvenile birds in either habitat remains unexplored. In this study, we used ptilochronology and feather corticosterone to compare the conditional state of juvenile chickadees in young and mature forest during two distinct periods of song learning - the sensory phase, which occurs prior to settlement, and the sensorimotor phase, which occurs post-settlement. A sample of juvenile males was captured and euthanized several weeks prior to their first breeding season to compare the development of song center nuclei and syrinx in both habitats. The corticosterone levels of natally-grown feathers were greater among birds that settled in mature than young forests - as these feathers were grown pre-settlement, they reflect differences in physiology during the sensory phase. This difference in conditional state is reflected by differences in syrinx and song center nuclei development later during the sensorimotor phase - birds in young forest have smaller syrinx, and moderately-larger RA, than birds in mature forest. Those differences could be responsible for the difference in consistency in song structure observed across habitats. The difference in physiological state across habitats, combined with potential compounding effect of differences in winter resources between habitats, could influence the difference in syrinx and neural development seen in juvenile males during the early spring, and influence the male's ability to learn and render their species-specific song.

Song performance and elaboration as potential indicators of male quality in Java sparrows

Bird songs have evolved under sexual selection pressure. Songs include multiple features that are subject to female preference, but recent comparative research has indicated evolutionary tradeoffs between song performance and complexity in some species. Trill, a repetition of the same sound, is a performance-related song trait; higher trill performance can be achieved at the cost of song complexity at the among-species or population level. The aim of this study was to examine whether such tradeoffs also account for within-species variation in Java sparrow songs, which include both multiple trill types and non-trill parts. We found a great individual variation in trill proportion, trill performance, and song complexity. A positive association between trill performance and body size suggested that trills can serve as an indicator of male quality. However, contrary to the tradeoffs predicted by previous studies based on other passerine species, trill performance and song complexity, i.e., note repertoire, were positively correlated: males in better condition can sing songs with larger note repertoires and higher trill performance, which may explain how trills and non-trill notes are both maintained and have co-evolved by sexual selection in Java sparrow songs.

Trill performance components vary with age, season, and motivation in the banded wren

Acoustic displays with difficult-to-execute sounds are often subject to strong sexual selection, because performance levels are related to the sender's condition or genetic quality. Performance may also vary with age, breeding stage, and motivation related to social context. We focused on within-male variation in four components of trill performance in banded wren (Thryophilus pleurostictus) songs: note consistency, frequency bandwidth, note rate and vocal deviation. The latter is a composite measure reflecting deviation from the performance limit on simultaneously maximizing both frequency bandwidth and note rate. We compared the changes in these song parameters at three time scales: over the course of years, across the breeding season, and at different times of the day with contrasting agonistic contexts. Vocal deviation decreased and note consistency increased over years, suggesting that experience may improve individual proficiency at singing trills. Consistency also increased across the season, confirming that practice is important for this parameter. Although there was no significant seasonal change in vocal deviation, one of its components, note rate, increased during the season. Neither vocal deviation nor consistency varied with agonistic context. However, note rate increased during playback experiments simulating territorial intrusions compared to dawn chorus singing. The magnitude of a male's increase in note rate was positively correlated with his aggressive behavior during the playback experiment. Thus consistency, bandwidth, and vocal deviation indicate age, whereas trill rate flexibly indicates the singer's aggressive motivation. We also found evidence of a within-male trade-off between vocal deviation and consistency.

Comparative analysis of mineralocorticoid receptor expression among vocal learners (Bengalese finch and budgerigar) and non-vocal learners (quail and ring dove) has implications for the evolution of avian vocal learning

Mineralocorticoid receptor is the receptor for corticosteroids such as corticosterone or aldosterone. Previously, we found that mineralocorticoid receptor was highly expressed in song nuclei of a songbird, Bengalese finch (Lonchura striata var. domestica). Here, to examine the relationship between mineralocorticoid receptor expression and avian vocal learning, we analyzed mineralocorticoid receptor expression in the developing brain of another vocal learner, budgerigar (Melopsittacus undulatus) and non-vocal learners, quail (Coturnix japonica) and ring dove (Streptopelia capicola). Mineralocorticoid receptor showed vocal control area-related expressions in budgerigars as Bengalese finches, whereas no such mineralocorticoid receptor expressions were seen in the telencephalon of non-vocal learners. Thus, these results suggest the possibility that mineralocorticoid receptor plays a role in vocal development of parrots as songbirds and that the acquisition of mineralocorticoid receptor expression is involved in the evolution of avian vocal learning.

Getting a head start: diet, sub-adult growth, and associative learning in a seed-eating passerine

Developmental stress, and individual variation in response to it, can have important fitness consequences. Here we investigated the consequences of variable dietary protein on the duration of growth and associative learning abilities of zebra finches, Taeniopygia guttata, which are obligate graminivores. The high-protein conditions that zebra finches would experience in nature when half-ripe seed is available were mimicked by the use of egg protein to supplement mature seed, which is low in protein content. Growth rates and relative body proportions of males reared either on a low-protein diet (mature seed only) or a high-protein diet (seed plus egg) were determined from body size traits (mass, head width, and tarsus) measured at three developmental stages. Birds reared on the high-protein diet were larger in all size traits at all ages, but growth rates of size traits showed no treatment effects. Relative head size of birds reared on the two diets differed from age day 95 onward, with high-diet birds having larger heads in proportion to both tarsus length and body mass. High-diet birds mastered an associative learning task in fewer bouts than those reared on the low-protein diet. In both diet treatments, amount of sub-adult head growth varied directly, and sub-adult mass change varied inversely, with performance on the learning task. Results indicate that small differences in head growth during the sub-adult period can be associated with substantial differences in adult cognitive performance. Contrary to a previous report, we found no evidence for growth compensation among birds on the low-protein diet. These results have implications for the study of vertebrate cognition, developmental stress, and growth compensation.

Expression patterns of mineralocorticoid and glucocorticoid receptors in Bengalese finch (Lonchura striata var. domestica) brain suggest a relationship between stress hormones and song-system development

Much evidence suggests that song traits function as an honest signal of male quality during mate choice in songbirds. Because songbirds learn vocalizations during the juvenile stage, development of the song system and song traits is affected by stressful conditions. However, it remains unknown how stressful conditions affect later song traits during development. To explore the relationship between glucocorticoids and song-system development, we performed in situ hybridization analysis of the glucocorticoid and mineralocorticoid receptors in juvenile and adult brains. The glucocorticoid receptor showed weak expression in song nuclei and strong expression in the hypothalamus, whereas the mineralocorticoid receptor showed strong song-nuclei-related expression. Thus, it appears that glucocorticoids are involved in song development directly by binding to receptors in song nuclei or indirectly by regulating sex hormones through hypothalamic hormones.

No heightened condition dependence of zebra finch ornaments--a quantitative genetic approach

The developmental stress hypothesis offers a mechanism to maintain honesty of sexually selected ornaments, because only high quality individuals will be able to develop full ornamentation in the face of stress during early development. Experimental tests of this hypothesis have traditionally involved the manipulation of one aspect of the rearing conditions and an examination of effects on adult traits. Here, we instead use a statistically powerful quantitative genetic approach to detect condition dependence. We use animal models to estimate environmental correlations between a measure of early growth and adult traits. This way, we could make use of the sometimes dramatic differences in early growth of more than 800 individually cross-fostered birds and measure the effect on a total of 23 different traits after birds reached maturity. We find strong effects of environmental growth conditions on adult body size, body mass and fat deposition, moderate effects on beak colour in both sexes, but no effect on song and plumage characters. Rather surprisingly, there was no effect on male attractiveness, both measured in mate choice trials and under socially complex conditions in aviaries. There was a trend for a positive effect of good growth conditions on the success at fertilizing eggs in males breeding in aviaries whereas longevity was not affected in either sex. We conclude that zebra finches are remarkably resilient to food shortage during growth and can compensate for poor growth conditions without much apparent life-history trade-offs. Our results do not support the hypothesis that sexually selected traits show heightened condition dependence compared to nonsexually selected traits.

Developmental stress affects song learning but not song complexity and vocal amplitude in zebra finches

Several recent studies have tested the hypothesis that song quality in adult birds may reflect early developmental conditions, specifically nutritional stress during the nestling period. Whilst all of these earlier studies found apparent links between early nutritional stress and song quality, their results disagree as to which aspects of song learning or production were affected. In this study, we attempted to reconcile these apparently inconsistent results. Our study also provides the first assessment of song amplitude in relation to early developmental stress and as a potential cue to male quality. We used an experimental manipulation in which the seeds on which the birds were reared were mixed with husks, making them more difficult for the parents to obtain. Compared with controls, such chicks were lighter at fledging; they were thereafter placed on a normal diet and had caught up by 100 days. We show that nutritional stress during the first 30 days of life reduced the birds' accuracy of song syntax learning, resulting in poorer copies of tutor songs. Our experimental manipulations did not lead to significant changes in song amplitude, song duration or repertoire size. Thus, individual differences observed in song performance features probably reflect differences in current condition or motivation rather than past condition.