Annual variation in vocal performance and its relationship with bill morphology in Lincoln's sparrows, Melospiza lincolnii

Morphology may affect behavioural performance through a direct, physical link or through indirect, secondary mechanisms. Although some evidence suggests that the bill morphology of songbirds directly constrains vocal performance, bill morphology may influence vocal performance through indirect mechanisms also, such as one in which morphology influences foraging and thus the ability to perform some types of vocal behaviour. This raises the possibility for ecologically induced variation in the relationship between morphology and behaviour. To investigate this, I used an information theoretic approach to examine the relationship between bill morphology and several measures of vocal performance in Lincoln’s sparrows (Melospiza lincolnii). I compared this relationship between two breeding seasons that differed markedly in ambient temperatures, phenology of habitat maturation, and food abundance. I found a strong curvilinear relationship between bill shape (height/width) and vocal performance in the seemingly less hospitable season but not in the other, leading to a difference between seasons in the population’s mean vocal performance. Currently, I do not know the cause of this annual variation. However, it could be due to the effects of bill shape on foraging and therefore on time budget, energy balance, or some other behavioural or physiological response that manifests mostly under difficult environmental conditions or, alternatively, to associations between male quality and both vocal performance and bill shape. Regardless of the cause, these results suggest the presence of an indirect, ecologically mediated link between morphology and behavioural performance, leading to annual variation in the prevailing environment of acoustic signals

Facultative Altitudinal Movements by Mountain White-Crowned Sparrows (Zonotrichia Leucophrys Oriantha) in the Sierra Nevada

Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) winter in Mexico and often arrive in the vicinity of their breeding grounds in the Sierra Nevada well before nesting is possible. Arrival at Tioga Pass, California (elevation 3,030 m), usually occurs in early May, but residual winter snow and adverse weather can delay nesting for weeks. We used radiotelemetry to determine whether prebreeding Mountain White-crowned Sparrows engaged in weather-related altitudinal movements during the waiting period between the end of spring migration and onset of breeding during 1995-2001, with a range of residual winter snowpacks. Interannual variation in arrival date and onset of egg laying was 18 and 41 days, respectively. We tracked females for two years and males for all seven years. During spring snowstorms (which occurred in four years), radiomarked individuals moved to lower elevation sites, where they often remained for several days. Departing birds left Tioga Pass by early afternoon and returned early in the morning after storms. More frequent storms during tracking increased the likelihood of facultative altitudinal movements, but heavier residual winter snowpack did not. Warm days increased the likelihood of birds returning to Tioga Pass from low elevation. This study demonstrates that facultative altitudinal movement behavior can be a common feature of spring arrival biology in montane-breeding birds. Received 1 November 2002, accepted 30 June 2004.Integrative Biolog

Sex Differences in Forebrain Monoaminergic Response to Song Performance

In many species, successful reproduction is dependent on the ability to adjust social behavior in response to an ever-changing social environment. Because a sexual signal's value and meaning can differ between females and males, responses to those signals should also differ. One way individuals can modulate social behavior is through experience-dependent modulation of the sensory systems that process social signals. Central monoamines (norepinephrine, dopamine, serotonin) modulate neural sensitivity to social stimuli and are key regulators of experience-dependent neuroplasticity in vertebrate sensory systems. However, few studies have examined how exposure to different sexual signals influences monoaminergic activity in female compared to male sensory systems. We used Lincoln's sparrows (Melospiza lincolnii) to examine sex differences in how variation in the trill performance of song influences central monoaminergic activity in the auditory telencephalon. Trill performance measures the rate at which a song syllable is produced relative to the syllable's frequency bandwidth and is thought to reflect the difficulty with which songs are produced. High-performance trills are more threatening to males but more attractive to females. We found that the effects of trill performance on monoaminergic activity were sex-dependent. Relative to the response to low-performance songs, exposure to high-performance songs decreased noradrenergic activity in the caudomedial nidopallium, and tended to decrease serotoninergic activity in the caudomedial mesopallium and caudomedial nidopallium of the auditory telencephalon in females, but in males, the monoamine measurements were indistinguishable between song treatments. These results suggest that the mechanisms underlying sensory processing of male sexual signals differ between the sexes

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

Independent effects of song quality and experience with photostimulation on expression of the immediate, early gene ZENK (EGR-1) in the auditory telencephalon of female European starlings

Age influences behavioral decisions such as reproductive timing and effort. In photoperiodic species, such age effects may be mediated, in part, by the individual's age-accrued experience with photostimulation. In female European starlings (Sturnus vulgaris) that do not differ in age, experimental manipulation of photostimulation experience (photoexperience) affects hypothalamic, pituitary, and gonadal activity associated with reproductive development. Does photoexperience also affect activity in forebrain regions involved in processing a social cue, the song of males, which can influence mate choice and reproductive timing in females? Female starlings prefer long songs over short songs in a mate-choice context, and, like that in other songbird species, their auditory telencephalon plays a major role in processing these signals. We manipulated the photoexperience of female starlings, photostimulated them, briefly exposed them to either long or short songs, and quantified the expression of the immediate-early gene ZENK (EGR-1) in the caudomedial nidopallium as a measure of activity in the auditory telencephalon. Using an information theoretic approach, we found higher ZENK immunoreactivity in females with prior photostimulation experience than in females experiencing photostimulation for the first time. We also found that long songs elicited greater ZENK immunoreactivity than short song did. We did not find an effect of the interaction between photoexperience and song length, suggesting that photoexperience does not affect forebrain ZENK-responsiveness to song quality. Thus, photoexperience affects activity in an area of the forebrain that processes social signals, an effect that we hypothesize mediates, in part, the effects of age on reproductive decisions in photoperiodic songbirds

Estradiol-dependent modulation of serotonergic markers in auditory areas of a seasonally breeding songbird.

Because no organism lives in an unchanging environment, sensory processes must remain plastic so that in any context, they emphasize the most relevant signals. As the behavioral relevance of sociosexual signals changes along with reproductive state, the perception of those signals is altered by reproductive hormones such as estradiol (E2). We showed previously that in white-throated sparrows, immediate early gene responses in the auditory pathway of females are selective for conspecific male song only when plasma E2 is elevated to breeding-typical levels. In this study, we looked for evidence that E2-dependent modulation of auditory responses is mediated by serotonergic systems. In female nonbreeding white-throated sparrows treated with E2, the density of fibers immunoreactive for serotonin transporter innervating the auditory midbrain and rostral auditory forebrain increased compared with controls. E2 treatment also increased the concentration of the serotonin metabolite 5-HIAA in the caudomedial mesopallium of the auditory forebrain. In a second experiment, females exposed to 30 min of conspecific male song had higher levels of 5-HIAA in the caudomedial nidopallium of the auditory forebrain than birds not exposed to song. Overall, we show that in this seasonal breeder, (1) serotonergic fibers innervate auditory areas; (2) the density of those fibers is higher in females with breeding-typical levels of E2 than in nonbreeding, untreated females; and (3) serotonin is released in the auditory forebrain within minutes in response to conspecific vocalizations. Our results are consistent with the hypothesis that E2 acts via serotonin systems to alter auditory processing

Contrast influences female attraction to performance-based sexual signals in a songbird

Animals do not make decisions in a bubble but often refer to previous experience when discriminating between options. Contrast effects occur when the value of a stimulus affects the response to another value of the stimulus, and the changes in value and response are in the same direction. Although contrast effects appear irrational, they could benefit decision makers when there is spatial or temporal variation and autocorrelation in the value of stimuli that elicit decisions. Here, we examined whether contrasts influence female evaluation of male performance-based sexual signals. We exposed female Lincoln's sparrows (Melospiza lincolnii) to one week of songs that we had experimentally reduced or elevated in performance, followed by a novel song of intermediate performance. We found that high-performance songs were more attractive to females than low-performance songs. Moreover, the intermediate songs were more attractive following exposure to low- than to high-performance songs. These results indicate that contrast can influence evaluation of performance-based sexual stimuli. By examining contrast effects in the ecologically relevant context of mate choice for performance, we can better understand both the adaptive value of comparative evaluation as well as the mechanisms that underlie variation in mate choice and sexual selection

Song environment affects singing effort and vasotocin immunoreactivity in the forebrain of male Lincoln's sparrows

Male songbirds often establish territories and attract mates by singing, and some song features can reflect the singer’s condition or quality. The quality of the song environment can change, so male songbirds should benefit from assessing the competitiveness of the song environment and appropriately adjusting their own singing behavior and the neural substrates by which song is controlled. In a wide range of taxa social modulation of behavior is partly mediated by the arginine vasopressin or vasotocin (AVP/AVT) systems. To examine the modulation of singing behavior in response to the quality of the song environment we compared the song output of laboratory-housed male Lincoln’s sparrows (Melospiza lincolnii) exposed to one week of chronic playback of songs categorized as either high or low quality, based on song length, complexity and trill performance. To explore the neural basis of any facultative shifts in behavior, we also quantified the subjects’ AVT immunoreactivity (AVT-IR) in three forebrain regions that regulate socio-sexual behavior: the medial bed nucleus of the stria terminalis (BSTm), the lateral septum (LS) and the preoptic area. We found that high quality songs increased singing effort and reduced AVT-IR in the BSTm and LS, relative to low quality songs. The effect of the quality of the song environment on both singing effort and forebrain AVT-IR raises the hypothesis that AVT within these brain regions plays a role in the modulation of behavior in response to competition that individual males may assess from the prevailing song environment