Browsing by Author "Peters, S"

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    Are song sequencing rules learned by song sparrows?
    (Animal Behaviour, 2022-10-01) Peters, S; Soha, J; Searcy, WA; Nowicki, S
    Although the effects of learning on song structure have been extensively studied in songbirds, little attention has been given to the learning of syntax at the level of song sequences. Here we investigate song syntax learning in two cohorts of hand-reared song sparrows, Melospiza melodia: an isolate group, consisting of four males raised with no exposure to external song models, and a trained group, consisting of 17 males exposed to recorded song sequences during the sensitive period for song learning. The isolate males followed three syntactical rules previously described for field-recorded song sparrows: (1) they produced their song type repertoires with eventual variety, repeating a song type multiple times before switching to another; (2) they cycled through their repertoires using close to the minimum number of bouts; and (3) they showed consistent preferences for singing certain of their song types more than others. The trained males were tutored with sequences with exaggerated eventual variety and cycling patterns and no usage preferences, but their syntax was little affected by any of these training features. One syntactical pattern that was affected by external experience was the rule that long bouts of a song type are followed by long recurrence intervals before that type is produced again. Isolate males showed no bout length/recurrence interval correlations while trained males showed reduced correlations relative to field-recorded males, implicating learning in the development of the normal pattern. Other songbird species have been found to preferentially use song type transitions as adults that they were tutored with as juveniles, but the trained song sparrows in this study showed no evidence of such effects.
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    Female swamp sparrows do not show evidence of discriminating between the songs of peak-aged and senescent males
    (Ethology, 2021-01-01) Zipple, MN; Peters, S; Searcy, WA; Nowicki, S
    Sexual selection theory predicts that females face contrasting selection pressures when choosing the age of their mate. On the one hand, older males have demonstrated their ability to survive and they may be more experienced than younger males. At the same time, however, younger males are expected to have accumulated fewer deleterious mutations in their germline as compared to older males. These contrasting pressures on female preference may result in a preference for intermediate-aged males. A preference for males of a particular age can only be expressed, however, if females are able to identify males of different ages. We have previously shown that male swamp sparrows display age-related changes in vocal quality, such that males display sharp increases in vocal quality in early adulthood, followed by gradual senescent declines thereafter. We have also shown that territorial males discriminate these within-individual differences, giving stronger aggressive responses to songs of peak-aged males than to those of senescent males. Here, we use a copulation solicitation assay to test whether females also discriminate these within-signaler markers of senescence in song. Contrary to our prediction, females did not show any evidence of discriminating between songs recorded from peak-aged males as compared to songs from the same males following song senescence. We suggest that this difference in demonstrated discrimination between males and females may be the result of the two sexes attending to different song characteristics.
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    Maturational changes in song sparrow song
    (Journal of Avian Biology, 2022-01-01) Kochvar, KH; Peters, S; Zipple, MN; Nowicki, S
    Age-related changes in the production of sexually selected assessment signals have been identified across a diverse range of taxa, and in some cases, these changes have been shown to affect receiver response to those signals. One important type of change occurs even after a signaler reaches breeding age, a phenomenon known as delayed maturation. Delayed maturation has been observed in the songs of several bird species, with potential fitness consequences for males as a byproduct of female choosiness or male competition. Here, we analyzed songs recorded across the first three years of life in a cohort of hand-reared song sparrows Melospiza melodia to detect early-life age-related changes in song. We focused on three measures of song complexity, including within song type variation, the average number of notes and the number of unique note types for the most common variant of each song type, and five measures of song production patterns, including singing rate, time interval between songs within a bout of the same song type, time interval between bouts (i.e. when the song type changes), within-song stereotypy and between-song consistency. All measures of song complexity and most measures of song production patterns (excluding within-song stereotypy) changed significantly within individuals as birds aged from one to two years as well as from one to three years (excluding within-bout time interval), whereas no significant changes occurred from two to three years of age. Based on these features, a linear discriminant model could distinguish between the song of young (age 1) and older (age 2 and 3) adult males, providing support that song could serve as an indicator of age in this species. We discuss potential implications of these results for mate choice and male–male competition in song sparrows.
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    Neural correlates of categorical perception in learned vocal communication.
    (Nat Neurosci, 2009-02) Prather, JF; Nowicki, S; Anderson, RC; Peters, S; Mooney, RA
    The division of continuously variable acoustic signals into discrete perceptual categories is a fundamental feature of vocal communication, including human speech. Despite the importance of categorical perception to learned vocal communication, the neural correlates underlying this phenomenon await identification. We found that individual sensorimotor neurons in freely behaving swamp sparrows expressed categorical auditory responses to changes in note duration, a learned feature of their songs, and that the neural response boundary accurately predicted the categorical perceptual boundary measured in field studies of the same sparrow population. Furthermore, swamp sparrow populations that learned different song dialects showed different categorical perceptual boundaries that were consistent with the boundary being learned. Our results extend the analysis of the neural basis of perceptual categorization into the realm of vocal communication and advance the learned vocalizations of songbirds as a model for investigating how experience shapes categorical perception and the activity of categorically responsive neurons.
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    Song performance improves with continued singing across the morning in a songbird
    (Animal Behaviour, 2020-09-01) Dinh, JP; Peters, S; Nowicki, S
    Vocal performance – an animal's ability to produce physically challenging vocalizations – can reflect a signaller's overall condition and can be a reliable signal of quality. It has been suggested recently that songbirds improve vocal performance through recent practice during intense dawn singing. We tested whether recent practice improves vocal performance in swamp sparrows, Melospiza georgiana, a species for which the biomechanical constraints and biological implications of vocal performance are well established. We measured vocal deviation – a measure of performance – in 1527 songs recorded from 11 captive swamp sparrows, four of which were developmentally stressed as juveniles. Vocal performance improved across the morning as a function of both the cumulative number of songs previously performed and the time of day. Song types with introductory syllables showed greater improvement than more typical song types composed solely of trilled syllables, and across all song types, as song output increased, the average improvement in vocal performance also increased. However, males with high song output exhibited greater variability in vocal performance, suggesting that some individuals might experience fatigue in song production. Furthermore, birds that had been developmentally stressed as juveniles showed greater improvement over the morning than birds that were not stressed. If conspecifics attend to within-individual variation in vocal performance, then improvement in vocal performance over the course of a day may drive birds to sing early and often, although fatigue may limit the extent to which this advantage may be gained.
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    Sounds of senescence: Male swamp sparrows respond less aggressively to the songs of older individuals
    (Behavioral Ecology, 2021-01-01) Zipple, MN; Peters, S; Searcy, WA; Nowicki, S
    Age-related changes in assessment signals occur in a diverse array of animals, including humans. Age-related decline in vocal quality in humans is known to affect perceived attractiveness by potential mates and voters, but whether such changes have functional implications for nonhuman animals is poorly understood. Most studies of age-related change in animal signals focus on increases in signal quality that occur soon after the age of first breeding (“delayed maturation”), but a few have shown that signal quality declines in older individuals after a mid-life peak (“behavioral senescence”). Whether other individuals are able to detect this senescent decline of assessment signals has not previously been tested. Here we use playback experiments to show that wild male swamp sparrows (Melospiza georgiana) respond more aggressively to songs from 2-year-old males as compared with songs from the same males when they are 10 years old. Senescence in signals that, like birdsong, affect reproductive success through intrasexual competition or mate choice may be of evolutionary significance. Lay Summary: Using playback experiments with wild swamp sparrows (Melospiza georgiana), we demonstrate that listeners both detect and respond to age-related declines in vocal quality. Two previous studies have shown that some song characteristics deteriorate with age later in life in songbirds, but to our knowledge this is the first demonstration outside of humans that such deterioration affects receiver response. Discrimination of songs from males of different ages may have evolutionary implications.
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    Variation in carotenoid-containing retinal oil droplets correlates with variation in perception of carotenoid coloration
    (Behavioral Ecology and Sociobiology, 2020-07-01) Caves, EM; Schweikert, LE; Green, PA; Zipple, MN; Taboada, C; Peters, S; Nowicki, S; Johnsen, S
    © 2020, The Author(s). Abstract: In the context of mate choice, males may vary continuously in their expression of assessment signals, typically reflecting information about variation in mate quality. Similarly, females may exhibit variation in mate preference, which could be due to differences in how individual females perceive signals. The extent to which perception varies across individuals, however, and whether differences in sensory physiology underlie perceptual differences is poorly understood. Carotenoid pigments create the orange-red coloration of many assessment signals, and they also play a role in color discrimination in many vertebrates via their presence in retinal oil droplets. Here, we link variation in oil droplet carotenoid concentration with the ability of female zebra finches (Taeniopygia guttata) to discriminate an orange-red color continuum that parallels variation in male beak color, a mate assessment signal. We have shown previously that zebra finch females perceive this color range categorically, meaning they label color stimuli from this continuum as belonging to two categories and exhibit better discrimination between colors from different categories as compared with equally different colors from within a category. We quantified behavioral color discrimination and R-type (red) cone oil droplet spectral absorption, a proxy for carotenoid concentration. Oil droplet absorption was strongly predictive of variation in behavioral color discrimination ability. In particular, higher carotenoid concentration in oil droplets correlated with increased discrimination of colors from different sides of the previously identified category boundary. These data show that differences in the sensory periphery can correlate with individual variation in perception of a signal-relevant color range. Significance statement: Signal receivers vary in their preferences for signaling traits, but whether this is due to variation in how different receivers perceive signals is not well-understood. We show that variation between individual zebra finch females in perception of an orange-red continuum range correlates with the carotenoid concentration of retinal oil droplets. These data provide the first direct evidence that individual variation in oil droplet carotenoid concentration can lead to variation in color discrimination ability. Linking variation in signal-relevant color discrimination ability with variation in retinal physiology suggests a potential mechanism contributing to individual variation in signal assessment.