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20 results for “bill size”
Data from: Shorebirds are shrinking and shape-shifting: Declining body size and lengthening bills in the past half-century
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Spatial variation in avian bill size is associated with temperature extremes in a major radiation of Australian passerines
<p>Morphology is integral to body temperature regulation. Recent advances in understanding of thermal physiology suggest a role of the avian bill in thermoregulation. To explore the adaptive significance of bill size for thermoregulation we characterized relationships between bill size and climate extremes. Most previous studies have focussed on climate means, ignoring extremes, and do not reflect thermoregulatory costs experienced over shorter time scales. Using 79 species (9,847 museum specimens), we explore how bill size variation is associated with temperature extremes in a large and diverse radiation of Australasian birds, Meliphagides. Overall, across the continent, bill size variation was associated with both climate extremes and means and was most strongly associated with winter temperatures; associations at the level of climate zones differed from continent-wide associations, were complex and non-linear, yet consistent with physiology and a thermoregulatory role for avian bills. We provide strong evidence that climate extremes have contributed to the evolution of bill morphology in relation to thermoregulation and demonstrate the importance of including extremes to understand fine-scale trait variation across space. Increasing frequency and intensity of climate extremes, a signature of climate change, may lead to changes in bill size, but this is yet to be tested.</p>
Measuring avian bill size: Comparing and evaluating 3D surface scanning with traditional size estimates in Australian birds
<p>Unidimensional measurements for estimating bill size, like length and width, are commonly used in ecology and evolution, but can be criticised due to issues with repeatability and accuracy. Furthermore, formula-based estimates of bill surface area tend to assume uniform bill shapes across species, which is rarely the case. 3D surface scanning can potentially help overcome some such issues by collecting detailed external morphology and direct measurements of surface area, rather than composite estimates of size. Here, we evaluate the use of 3D surface scanners on avian museum specimens to test the repeatability of 3D-based measurements and compare these to traditional formula-based methods of estimating bill size from unidimensional measurements. Using 28 Australian bird species, we investigate inter-observer repeatability of surface area measurements from 3D surface scans. We then compare 3D-based size estimates to formula-based size estimates to infer the accuracy and precision of formula-based measurements of bill surface area. We find that morphometric measurements from 3D surface scans are highly repeatable between observers, without the need for extensive training, demonstrating an advantage over unidimensional measuring methods, like callipers. When comparing 3D-based measurements to formula-based estimates of bill surface area, most formulae for estimating size consistently underestimate surface area, and with considerable variation between species. Where 3D scanning is not possible, we find that a commonly used cone formula for estimating bill size is most precise across diverse bill shapes, therefore supporting its use in interspecific contexts. However, we find that incorporating an additional unidimensional measure of bill curvature into formulae improves the accuracy of the calculated area. Our results reveal the high potential for 3D surface scanners in avian morphometric research, especially for studies necessitating large sample sizes collected by multiple observers, and gives suggestions for formula-based approaches to estimate bill size.</p>
Relationship between Channel Island Melospiza melodia (Song Sparrow) bill size and vegetation, seed extraction time, bite force, and climate (2014-2016)
<p>Inferring the environmental selection pressures responsible for phenotypic variation is a challenge in adaptation studies as traits often have multiple functions and are shaped by complex selection regimes. We provide indirect evidence that morphology of the multifunctional avian bill is primarily shaped by climate and thermoregulatory ability in <em>Melospiza melodia</em> (Song Sparrows) on the California Channel Islands. Our research builds on a study in Song Sparrow museum specimens that demonstrated a positive correlation between bill surface area and maximum temperature, suggesting a greater demand for dry heat dissipation in hotter, xeric environments. We sampled contemporary sparrow populations across three climatically distinct islands to test the hypotheses that bill morphology is influenced by habitat differences with functional consequences for foraging efficiency and is related to maximum temperature and, consequently, important for thermoregulation. Measurements of >500 live individuals indicated a significant, positive relationship between maximum temperature and bill surface area when correcting for body size. In contrast, maximum bite force, seed extraction time, and vegetation on breeding territories (a proxy for food resources) were not significantly associated with bill dimensions. While we cannot exclude the influence of foraging ability and diet on bill morphology, our results are consistent with the hypothesis that variation in Song Sparrows' need for thermoregulatory capacity across the northern Channel Islands selects for divergence in bill surface area.</p>
Bill size, bill shape, and body size constrain bird song evolution on a macroevolutionary scale
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Spatial variation in avian bill size is associated with temperature extremes in a major radiation of Australian passerines
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Measuring avian bill size: Comparing and evaluating 3D surface scanning with traditional size estimates in Australian birds
Open the record for dataset details and reuse information.
Relationship between Channel Island Melospiza melodia (Song Sparrow) bill size and vegetation, seed extraction time, bite force, and climate (2014-2016)
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Data from: Geographical variation in bill size provides evidence for Allen's rule in a cosmopolitan raptor
Aim. Avian beak morphology is a good example of how anatomical structures evolved in response to different selective pressures, such as diet and vocalizations, but also thermoregulation. The latter function was neglected until recently, but convincing evidence has been provided about the birds' capacity to regulate heat dissipation through their highly vascularized bill. According to this adaptive function and coherently with the ecogeographical "Allen's rule", which predicts smaller body appendages in colder climates, large beaks should be favoured in warm environments. Here, we tested this prediction in the cosmopolitan common barn owl group. Location. World Time period. 1809-2017 Major taxa studied. Tyto alba species complex Methods. We analysed the variation in bill length relative to body size according to temperature, latitude and elevation in 7619 barn owls. The specimens were collected by 140 museums, and represent three distinct evolutionary lineages, occurring in geographically separated regions and covering the entire distribution range of the species complex: the Afro-Palearctic Tyto alba, the Australasian T. javanica, and the American T. furcata. Results. In the three lineages, bill becomes larger with increasing temperature. This convergent pattern of evolution of smaller bills in colder climates is associated with a latitudinal variation in temperature, as small-billed individuals occurred at higher latitudes than conspecifics living closer to the Equator. Moreover, in T. furcata large-billed birds mostly occur at lower elevation closer to the Equator, bill length decreasing progressively with concomitant increase in latitude and elevation. Discussion. These findings provide evidence of repeated evolution of bill size on a global scale that is compatible with the Allen's rule. These results suggest a role of the bill as a potential heat-exchange surface, also in nocturnal raptors, which are not directly exposed to solar radiation and whose bill shape primarily evolved to hunt and consume animal prey.
Data from: Stable isotopes reveal differences in diet among reed bunting subspecies that vary in bill size
Reed bunting (Emberiza schoeniclus) subspecies vary considerably in bill size and shape and seem to be at an early stage of speciation, in which bill might be indirectly causing reproductive isolation. Hence, we evaluated whether bill size, as well as age and sex, are associated with foraging niche in three West European subspecies of reed bunting: the thin-billed schoeniclus, the intermediate-billed lusitanica and the thick-billed witherbyi. Blood sampling was undertaken at three sites in southwest Europe during the winter (when these subspecies co-occur), and stable isotope analyses (carbon and nitrogen) were performed to assess their foraging niches. Stable isotope analyses of potential food items confirmed uniform baseline isotopic composition among sites. schoeniclus showed a significantly broader isotopic niche than lusitanica and witherbyi, which seemed otherwise similar despite the fact that witherbyi is more divergent in bill traits. Stable isotope ratios were consistent with the latter two subspecies feeding on C3-plant-feeding insects, whereas schoeniclus diet also included C4 plant material. Despite its lower sexual dimorphism, sex and age differences were found only in schoeniclus, but these differences vary between locations in a complex manner. Our results suggest that bill size and shape differentiated between northern, migratory and southern, resident subspecies as a consequence of natural selection through competition during the winter, which is now reflected in isotopic niche divergence between subspecies. The potential roles of sexual selection, reed thickness and summer temperature on the difference in bill size (and greater sexual dimorphism) between lusitanica and witherbyi are discussed.
Data from: Ecological adaptation and birdsong: how body and bill sizes affect passerine sound frequencies
<p>The avian bill is finely adjusted to foraging ecology and, as part of the vocal tract, it may also affect sexual signals such as songs. Acoustic theory predicts that larger bills lower the resonant frequency of vocal tracts, allowing larger-billed species to emphasize lower sound frequencies. Theory also predicts that larger-billed species can change bill gape so as to sing over a wider frequency bandwidth. We tested these associations between bill size and sound frequencies of song across ca. 1000 taxonomically-diverse passerines. Phylogenetically informed analyses indicated that both bill and body sizes are negatively related to the sound frequency of songs, with additive effects of similar strength. Analyses of reduced datasets, to decrease bill-body size associations, indicated that the effect of bill size it is not an artefact of its covariation with body size. Sound frequency bandwidth was only related to body size but not bill size, perhaps because large bills may allow greater modulation of frequency but also hinder fast bill movement. Since the bill has a major role explaining species differences in birdsong sound frequency, it can be a magic trait that promotes reproductive isolation as a consequence of ecological divergence.</p>
Data from: Trophic niche width increases with bill size variation in a generalist passerine: a test of the niche variation hypothesis
1. The niche variation hypothesis (NVH) predicts that populations with wider niches are phenotypically more variable than populations with narrower niches, which is frequently used to explain diversifying processes such as ecological release. However, not all empirical evidence supports the NVH. Furthermore, a relationship between population phenotypic variation and niche width can be caused by sexual selection or environmental gradients, which should be carefully considered along with competition in explaining niche variation. 2. In this study we used eight populations of a generalist passerine species, Paradoxornis webbianus (vinous-throated parrotbill), to test the NVH. We assessed evidence of ecological sexual dimorphism and environmental gradients in bill morphology of P. webbianus. A total of 170 P. webbianus from eight sites ranging 24-2,668 m in altitude were included in this study. We used two principal components to quantify bill morphology, one describes bill size and the other describe bill slenderness. We used stable carbon and nitrogen isotope values of bird feathers to quantify trophic positions, and we estimated population trophic niche width using Bayesian standardized ellipse area. 3. Paradoxornis webbianus with larger and more slender bills fed at higher trophic levels and population trophic niche width tended to increase with bill size variation, supporting the NVH. The males had larger bills and marginally higher nitrogen isotope values than the females, suggesting ecological sexual dimorphism. Despite a positive correlation between bill size and wing length indicating sexual selection for larger male size, only three of the eight populations showed both male-biased bill size and male-biased wing length. Sexual dimorphism explained 13%-64% of bill size variation across sites, suggesting its role in niche variation could vary greatly among populations. The variation in bill slenderness in P. webbianus increased with elevation. However, neither bill size variation nor trophic niche width changed with elevation. Therefore, environmental gradients that could be reflected in the elevation are not likely to drive the observed morphological and niche variation. 4. This study provides an empirical case for the NVH and highlights the importance to investigate sexual dimorphism and environmental gradients in the studies of niche dynamics.
Data from: Geographical variation in bill size across bird species provides evidence for Allen’s rule
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Data from: Geographical variation in bill size provides evidence for Allen’s rule in a cosmopolitan raptor
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Data from: Shared temporal increases in bill size among songbirds of the San Francisco bay area are due to different seasonal selective pressures
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Data from: Trophic niche width increases with bill size variation in a generalist passerine: a test of the niche variation hypothesis
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Data from: Ecological adaptation and birdsong: how body and bill sizes affect passerine sound frequencies
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Data from: Stable isotopes reveal differences in diet among reed bunting subspecies that vary in bill size
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Data from: The influence of spatially heterogeneous anthropogenic change on bill size evolution in a coastal songbird
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Morphometrics of taxa in the genus Sphenopsis, recorded from adult male (n = 21) and female (n = 15) study skins in the Academy of Natural Sciences of Drexel University, Philadelphia (ANSP) and Delaware Museum of Nature & Science, Greenville (DMNH) collections. Sample sizes and means (± SD) are given for each taxon, within each sex class (female, male), for the following variables: (WG) wing length, (TR) tarsometatarsus length, (TL) tail length, (BL) bill length, and (BW) bill width. All measurements in mm. in Taxonomic status of the Western Hemispingus Sphenopsis ochracea (Thraupidae) and a review of species limits in the genus Sphenopsis P. L. Sclater, 1861
Morphometrics of taxa in the genus Sphenopsis, recorded from adult male (n = 21) and female (n = 15) study skins in the Academy of Natural Sciences of Drexel University, Philadelphia (ANSP) and Delaware Museum of Nature & Science, Greenville (DMNH) collections. Sample sizes and means (± SD) are given for each taxon, within each sex class (female, male), for the following variables: (WG) wing length, (TR) tarsometatarsus length, (TL) tail length, (BL) bill length, and (BW) bill width. All measurements in mm.
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OpenNeuro
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