Avian vocal mimicry has been studied for decades, but little is known about its function or requi... more Avian vocal mimicry has been studied for decades, but little is known about its function or requirements for accurate imitation. Furthermore, progress is hampered by the difficulty in identifying which vocalizations are indeed mimetic. We tested historical claims of vocal mimicry in the brown thornbill, Acanthiza pusilla, using a combination of human and computer methods to identify mimicry, followed by comparisons of acoustic similarity with model vocalizations. We recorded vocalizations of brown thornbills and sympatric heterospecifics while undisturbed and during mist net capture or the presence of natural or model predators. We then cross-validated human classification of mimicry with computer classification based on spectrographic measurements and spectral cross-correlation. Finally, we quantified the accuracy of the most common imitations. Brown thornbills predominantly imitated alarm calls given by heterospecifics towards aerial predators, which function in these models to provoke immediate flight by receivers. Human and computer-based methods produced consistent results when identifying and classifying mimicry. Mimicked aerial alarms were not perfect imitations of their corresponding model alarms, but did retain specific acoustic properties previously shown to be important for provoking immediate alarm responses. Although less accurate mimicry may reflect physiological constraints, we suggest that mimetic function, perhaps startling predators, only requires mimicry to retain features of model alarms that provoke immediate alarm responses by receivers. Understanding what factors influence the acoustic structure of mimetic vocalizations is essential in understanding the evolution of vocal mimicry, particularly with accumulating evidence that mimetic function does not always require perfect resemblance in other sensory modalities.► We evaluated vocal mimicry in the brown thornbill. ► Brown thornbills predominantly imitated other species' aerial alarm calls. ► Imitations were similar but not identical to corresponding model alarms. ► Inaccurate imitations retained features important for immediate alarm response. ► We suggest alarm calls may not require perfect imitation for function.
Subtle sexual dimorphism and its perception in apparently monomorphic bird species warrant assess... more Subtle sexual dimorphism and its perception in apparently monomorphic bird species warrant assessment of how birds identify the sex of conspecifics, particularly of prospective mates. Visual sensitivity and its potential co-variation with cryptic sexual dichromatism are still uninvestigated in most avian taxa. Using molecular sexing, reflectance spectrometry and perceptual modelling based on the sequencing of short wavelength visual pigments, we assessed the sex-specificity of coloration and colour perception in the red-tailed tropicbird Phaethon rubricauda. We also measured morphological dimorphism at a previously unstudied breeding locality for this species. Our data are in line with both physical and avian-perceived monochromatism with a potential indication of achromatic sex differences in plumage reflectance. The moderate extent of size dimorphism is consistent with reports from other Pacific breeding populations, and morphological measurements from live specimens in this study are in line with reports on museum specimens from the same sample location. Potential differences between individuals of the same sex in size and coloration warrant the assessment of sexual dimorphism in larger sample sizes of this species.
ABSTRACT The study of avian eggshell structure, including composition, pigmentation, thickness, a... more ABSTRACT The study of avian eggshell structure, including composition, pigmentation, thickness, and strength, has important ecological and economic implications. Previous investigators have used a variety of techniques to derive either direct measures or indirect estimates of eggshell thickness. Assessing the repeatability and method agreement of different techniques is necessary to permit comparison of eggshell thickness values from different studies on various genetic stocks, populations, and species. We recorded and analyzed measurements of eggshell thickness using two methods, micrometers and scanning electron microscopy (SEM), for several Palaeognathae and Neognathae taxa, including nonpasserines and passerines. Applying a tolerance-interval approach, we found that repeatability of measurements for eggs with thinner shells (<300 μm, all Neognathae taxa) was worse than for eggs with thicker shells (Palaeognathae taxa), but was still statistically and biologically reasonable given that the relative magnitude of intramethod agreements was <11%. Our results support previous predictions that measurements made using a micrometer are comparable to those made using SEM. This finding is particularly important given the relative ease and cost efficiency of the micrometer method. Importantly, these new analyses can be used to validate the use of published data from previous studies of micrometer-based eggshell thickness for both intra- and interspecific comparisons.El estudio de la estructura del cascarón de los huevos de aves, incluyendo su composición, pigmentación, grosor y fortaleza, tiene implicaciones ecológicas y económicas de importancia. Los trabajos que se han publicado sobre el grosor del cascarón utilizan una amplia variedad de técnicas para determinar directamente el grosor o hacer estimados indirectos. La forma de poder repetir las medidas y el método a seleccionarse, entre diferentes técnicas, es necesario para poder comparar el grosor del cascarón en diferentes estudios ya sea de diferentes grupos genéticos, poblaciones o especies. Nosotros tomamos y analizamos las medidas del grosor de cascarones de huevos utilizando dos métodos: el uso del micrómetro y un microscopio electrónico de barrido (MEB). Estos se utilizaron tanto en Palaeognathae y Neognathae, incluyendo paserinos, como no-paserinos. Aplicando un enfoque de intérvalo de tolerancia, encontramos que el repetir una medida para huevos con cascarón fino (<300 μm, todos de Neognathae), era peor que para huevo con cascarón más gruesos (Palaeognathae), aunque biológico y estadísticamente razonables, dado el caso de que la magnitud relativa de armonía entre métodos, fue <11%. Nuestros resultados apoyan predicciones previas de que las medidas tomadas usando un micrómetro son comparables a aquellas tomadas con un MEB. Esto es particularmente importante por que el método del micrómetro es fácil y costo efectivo. Más importante aún es que este estudio comparativo permite el validar los datos publicados en estudios previos utilizando micrómetros para determinar el grosor de los huevos, tanto en estudios intra- como inter-específicos.
The known chemical basis of diverse avian eggshell coloration is generated by the same two classe... more The known chemical basis of diverse avian eggshell coloration is generated by the same two classes of tetrapyrrole pigments in most living birds. We aimed to extend the evolutionary scope of these patterns by detecting pigments from extinct birds’ eggs. In our samples biliverdin was successfully extracted from subfossil shell fragments of the blue-green egg-laying upland moa Megalapteryx didinus, while protoporphyrin was extracted from the beige eggs of two other extinct moa species. Our data on pigment detection from eggshells of other extant paleognath birds, together with published information on other modern lineages, confirm tetrapyrroles as ubiquitous and conserved pigments contributing to diverse eggshell colours throughout avian evolution.
Avian vocal mimicry has been studied for decades, but little is known about its function or requi... more Avian vocal mimicry has been studied for decades, but little is known about its function or requirements for accurate imitation. Furthermore, progress is hampered by the difficulty in identifying which vocalizations are indeed mimetic. We tested historical claims of vocal mimicry in the brown thornbill, Acanthiza pusilla, using a combination of human and computer methods to identify mimicry, followed by comparisons of acoustic similarity with model vocalizations. We recorded vocalizations of brown thornbills and sympatric heterospecifics while undisturbed and during mist net capture or the presence of natural or model predators. We then cross-validated human classification of mimicry with computer classification based on spectrographic measurements and spectral cross-correlation. Finally, we quantified the accuracy of the most common imitations. Brown thornbills predominantly imitated alarm calls given by heterospecifics towards aerial predators, which function in these models to provoke immediate flight by receivers. Human and computer-based methods produced consistent results when identifying and classifying mimicry. Mimicked aerial alarms were not perfect imitations of their corresponding model alarms, but did retain specific acoustic properties previously shown to be important for provoking immediate alarm responses. Although less accurate mimicry may reflect physiological constraints, we suggest that mimetic function, perhaps startling predators, only requires mimicry to retain features of model alarms that provoke immediate alarm responses by receivers. Understanding what factors influence the acoustic structure of mimetic vocalizations is essential in understanding the evolution of vocal mimicry, particularly with accumulating evidence that mimetic function does not always require perfect resemblance in other sensory modalities.► We evaluated vocal mimicry in the brown thornbill. ► Brown thornbills predominantly imitated other species' aerial alarm calls. ► Imitations were similar but not identical to corresponding model alarms. ► Inaccurate imitations retained features important for immediate alarm response. ► We suggest alarm calls may not require perfect imitation for function.
Subtle sexual dimorphism and its perception in apparently monomorphic bird species warrant assess... more Subtle sexual dimorphism and its perception in apparently monomorphic bird species warrant assessment of how birds identify the sex of conspecifics, particularly of prospective mates. Visual sensitivity and its potential co-variation with cryptic sexual dichromatism are still uninvestigated in most avian taxa. Using molecular sexing, reflectance spectrometry and perceptual modelling based on the sequencing of short wavelength visual pigments, we assessed the sex-specificity of coloration and colour perception in the red-tailed tropicbird Phaethon rubricauda. We also measured morphological dimorphism at a previously unstudied breeding locality for this species. Our data are in line with both physical and avian-perceived monochromatism with a potential indication of achromatic sex differences in plumage reflectance. The moderate extent of size dimorphism is consistent with reports from other Pacific breeding populations, and morphological measurements from live specimens in this study are in line with reports on museum specimens from the same sample location. Potential differences between individuals of the same sex in size and coloration warrant the assessment of sexual dimorphism in larger sample sizes of this species.
ABSTRACT The study of avian eggshell structure, including composition, pigmentation, thickness, a... more ABSTRACT The study of avian eggshell structure, including composition, pigmentation, thickness, and strength, has important ecological and economic implications. Previous investigators have used a variety of techniques to derive either direct measures or indirect estimates of eggshell thickness. Assessing the repeatability and method agreement of different techniques is necessary to permit comparison of eggshell thickness values from different studies on various genetic stocks, populations, and species. We recorded and analyzed measurements of eggshell thickness using two methods, micrometers and scanning electron microscopy (SEM), for several Palaeognathae and Neognathae taxa, including nonpasserines and passerines. Applying a tolerance-interval approach, we found that repeatability of measurements for eggs with thinner shells (<300 μm, all Neognathae taxa) was worse than for eggs with thicker shells (Palaeognathae taxa), but was still statistically and biologically reasonable given that the relative magnitude of intramethod agreements was <11%. Our results support previous predictions that measurements made using a micrometer are comparable to those made using SEM. This finding is particularly important given the relative ease and cost efficiency of the micrometer method. Importantly, these new analyses can be used to validate the use of published data from previous studies of micrometer-based eggshell thickness for both intra- and interspecific comparisons.El estudio de la estructura del cascarón de los huevos de aves, incluyendo su composición, pigmentación, grosor y fortaleza, tiene implicaciones ecológicas y económicas de importancia. Los trabajos que se han publicado sobre el grosor del cascarón utilizan una amplia variedad de técnicas para determinar directamente el grosor o hacer estimados indirectos. La forma de poder repetir las medidas y el método a seleccionarse, entre diferentes técnicas, es necesario para poder comparar el grosor del cascarón en diferentes estudios ya sea de diferentes grupos genéticos, poblaciones o especies. Nosotros tomamos y analizamos las medidas del grosor de cascarones de huevos utilizando dos métodos: el uso del micrómetro y un microscopio electrónico de barrido (MEB). Estos se utilizaron tanto en Palaeognathae y Neognathae, incluyendo paserinos, como no-paserinos. Aplicando un enfoque de intérvalo de tolerancia, encontramos que el repetir una medida para huevos con cascarón fino (<300 μm, todos de Neognathae), era peor que para huevo con cascarón más gruesos (Palaeognathae), aunque biológico y estadísticamente razonables, dado el caso de que la magnitud relativa de armonía entre métodos, fue <11%. Nuestros resultados apoyan predicciones previas de que las medidas tomadas usando un micrómetro son comparables a aquellas tomadas con un MEB. Esto es particularmente importante por que el método del micrómetro es fácil y costo efectivo. Más importante aún es que este estudio comparativo permite el validar los datos publicados en estudios previos utilizando micrómetros para determinar el grosor de los huevos, tanto en estudios intra- como inter-específicos.
The known chemical basis of diverse avian eggshell coloration is generated by the same two classe... more The known chemical basis of diverse avian eggshell coloration is generated by the same two classes of tetrapyrrole pigments in most living birds. We aimed to extend the evolutionary scope of these patterns by detecting pigments from extinct birds’ eggs. In our samples biliverdin was successfully extracted from subfossil shell fragments of the blue-green egg-laying upland moa Megalapteryx didinus, while protoporphyrin was extracted from the beige eggs of two other extinct moa species. Our data on pigment detection from eggshells of other extant paleognath birds, together with published information on other modern lineages, confirm tetrapyrroles as ubiquitous and conserved pigments contributing to diverse eggshell colours throughout avian evolution.
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