Bill Shapes Research Articles

Measuring avian bill size: comparing and evaluating 3D surface scanning with traditional size estimates in Australian birds

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.

Widespread convergent morphological evolution within the largest family of songbirds.

Although convergence is a common evolutionary phenomenon, few studies have quantified its prevalence across a large, densely sampled clade. Large-scale phylogenies and the advent of novel computational methods facilitate more robust identification of convergent events and their statistical significance. The tanagers (Aves: Thraupidae), the largest family of songbirds, offer an excellent opportunity to study the extent of phenotypic convergence in response to similar ecological pressures on a continental scale. To investigate convergence in the group, we used the largest phylogenetic and multivariate morphological dataset to date for the clade. First, we used phylogenetic comparative analyses to show a correlation between diet and aspects of bill shape. We then investigated our dataset for the presence and magnitude of convergent events and assessed significance through simulations and modeling analyses. Overall, we found that around half (45.3%) of species and clades we tested have converged in morphological space more than would be expected by chance alone. Our study shows that across Thraupidae, various bill shapes have evolved convergently to fill multiple distinct sections of ecological niche space, reflecting a signal of ecological opportunity and structural constraints.

Forbidden links, trait matching and modularity in plant-hummingbird networks: Are specialized modules characterized by higher phenotypic floral integration?

BackgroundPlant-pollinator mutualistic networks show non-random structural properties that promote species coexistence. However, these networks show high variability in the interacting species and their connections. Mismatch between plant and pollinator attributes can prevent interactions, while trait matching can enable exclusive access, promoting pollinators’ niche partitioning and, ultimately, modularity. Thus, plants belonging to specialized modules should integrate their floral traits to optimize the pollination function. Herein, we aimed to analyze the biological processes involved in the structuring of plant-hummingbird networks by linking network morphological constraints, specialization, modularity and phenotypic floral integration.MethodsWe investigated the understory plant-hummingbird network of two adjacent habitats in the Lacandona rainforest of Mexico, one characterized by lowland rainforest and the other by savanna-like vegetation. We performed monthly censuses to record plant-hummingbird interactions for 2 years (2018–2020). We also took hummingbird bill measurements and floral and nectar measurements. We summarized the interactions in a bipartite matrix and estimated three network descriptors: connectance, complementary specialization (H2’), and nestedness. We also analyzed the modularity and average phenotypic floral integration index of each module.ResultsBoth habitats showed strong differences in the plant assemblage and network dynamics but were interconnected by the same four hummingbird species, two Hermits and two Emeralds, forming a single network of interaction. The whole network showed low levels of connectance (0.35) and high specialization (H2’ = 0.87). Flower morphologies ranged from generalized to specialized, but trait matching was an important network structurer. Modularity was associated with morphological specialization. The Hermits Phaethornis longirostris and P. striigularis each formed a module by themselves, and a third module was formed by the less-specialized Emeralds: Chlorestes candida and Amazilia tzacatl. The floral integration values were higher in specialized modules but not significantly higher than that formed by generalist species.ConclusionsOur findings suggest that biological processes derived from both trait matching and “forbidden” links, or nonmatched morphological attributes, might be important network drivers in tropical plant-hummingbird systems while morphological specialization plays a minor role in the phenotypic floral integration. The broad variety of corolla and bill shapes promoted niche partitioning, resulting in the modular organization of the assemblage according to morphological specialization. However, more research adding larger datasets of both the number of modules and pollination networks for a wider region is needed to conclude whether phenotypic floral integration increases with morphological specialization in plant-hummingbird systems.

Bird Evolution: Convergence Fits the Bill

New fossils help pinpoint when some birds started relying on a seed-based diet and reveal that disparate bill shapes evolved repeatedly throughout bird evolutionary history.

Diet of tropical insectivorous birds in lowland Malaysian rainforest

ABSTRACTDespite the importance of diet in avian ecology, knowledge of bird diet in tropical regions, particularly South-East Asia, is limited. Assessing predator–prey relationships of how energy flows across ecosystems provides insight into niche segregation of sympatric species. We examined induced-regurgitation samples from 15 species of insectivorous birds – 12 babblers and three flycatcher-like species – from the Krau Wildlife Reserve, central Peninsular Malaysia. The main objective of this study was to compare and characterise the diet of similar trophically insectivorous birds so as to examine the occurrence of dietary overlap or segregation. The majority of identified prey items belong to the following arthropod taxa: Coleoptera (53%), Hymenoptera (19%), Blattodea (11%), and Araneae (11%). The diet of all bird species slightly overlapped (p = 0.070) but network analysis yielded a relatively low value (Ro = 0.53), indicating dietary divergence may have occurred among the studied bird species, possibly reflected by the variation in proportion of arthropod groups. A high proportion of Coleoptera and three other arthropod groups (i.e. Hymenoptera, Blattodea and Araneae) in the diet of studied birds could be related to their richness and abundance in aerial leaf-litter, the substrate preferred by most babblers. Dietary differences may further be explained by variations in bill shapes and sizes, likely corresponding to prey size. Unique foraging strategies (utilising different vertical strata, microhabitats, and attack manoeuvres) could also lead to dietary separation among sympatric species. Flycatcher-like species were expected to flycatch different prey items (families or lower taxa) versus the gleaning birds (most babblers). This study successfully discerned more details on the diets of insectivorous birds inhabiting Malaysian forests, providing a foundation for future studies on the ecology and biology of understorey birds.

New species of Primozygodactylus from Messel and the ecomorphology and evolutionary significance of early Eocene zygodactylid birds (Aves, Zygodactylidae)

Zygodactylids (Zygodactylidae) are the extinct sister taxon of passerines (Passeriformes) and among the more abundant small arboreal birds in the early Eocene German fossil site Messel. Four species of the taxon Primozygodactylus have previously been identified and here two new species are described. In addition, new fossils of the poorly known P. eunjooae are reported. The fossils corroborate the presence of two very long central tail feathers for Primozygodactylus, and the feathering of the taxon corresponds with that of extant birds foraging in scrub and undergrowth. Species diversity of zygodactylids falls short of that of passerines, the most species-rich extant avian clade, and in bill shapes they also do not reach the diversity seen in extant Passeriformes. Because zygodactylids closely resemble passerines in skeletal morphology, the evolutionary success of passerines is unlikely to be due to particular skeletal features. Passerines and zygodactylids coexisted in Europe from the early Oligocene to the middle Miocene, and both groups probably differed in ecological characteristics. The zygodactyl foot of zygodactylids may have represented an adaptation for clinging to tree trunks, and if nesting in tree cavities, zygodactylids may have succumbed to competition for safe nesting places with avian or mammalian competitors.http://zoobank.org/urn:lsid:zoobank.org:pub:7F142141-7E1F-4568-89BF-E2363D128C36

Weather-Related Winter Mortality of Eurasian Oystercatchers (Haematopus ostralegus) in the Northeastern Wadden Sea

Strong winters may increase mortality in avian species, with potentially severe consequences for populations. A period of 10 cold days during an otherwise mild winter occurred in the Wadden Sea during February 2012, causing a mass mortality of more than 1,100 Eurasian Oystercatchers (Haematopus ostralegus). This study investigated whether mortality was highest in certain bird-classes (sex, age, diet specialization). By comparing dead with live individuals captured before and after the cold spell, significantly more immature Eurasian Oystercatchers were found dead (> 60%) than expected. Sex ratio did not differ significantly between dead and live individuals, the proportion of males being higher in both dead and live birds. All the dead individuals collected showed significantly smaller body masses (overall mean: 324 g) than live ones (overall mean: 457 g). Few individuals showed internal lesions or anatomical abnormalities, and no influenza virus was found. Dead Eurasian Oystercatchers had completely empty stomachs in 25% and 37% of the individuals in both study areas, Büsum and Amrum, respectively; all other individuals showing only few prey remains. The most frequent prey items were common cockles (Cerastoderma edule). Based on bill shapes, most of the dead Eurasian Oystercatchers were bivalve specialists, and fewer than expected worm eaters died. From band recoveries (n = 19), many of the dead individuals originated from Scandinavia (37%). The main reason for the high mortality appeared to be low food availability and quality before the cold spell combined with sudden low temperatures.

Hatching Order and Seasonal Timing of Development Predict Bill Morphology of Nestling and Adult Lincoln’s Sparrows

Traits under strong directional or stabilizing selection can nonetheless vary considerably if the selective forces impinging on them vary in strength or direction. Although such variation is commonly manifested between unrelated individuals, some of the largest differences occur between siblings because of differences in their developmental experience. This is exemplified by the broods of altricial birds, in which asynchronous hatching produces a competitive hierarchy that influences an individual's developmental rate and fitness. Using Lincoln's Sparrow (Melospiza lincolnii), I examined whether the order of hatching or the seasonal timing of development (another factor that influences offspring fitness and estimated as the date of initiation of the clutch from which an individual hatched) predicted variation in bill shape, a trait often under strong natural and sexual selection. I measured individuals as nestlings and as adults for a metric of bill shape (height/width) that is associated with an adult male Lincoln's Sparrow's song performance. I found that an individual's bill shape during the nestling stage positively correlated with its bill shape during the adult stage. Nestling bill shape declined (became wider and flatter in cross-section) with hatching order, and the bill shape of both nestlings and adults declined with the individual's seasonal timing of development. These findings raise the possibility of a trade-off between life stages in the optimization of songbird bill morphology and may explain the persistence of suboptimal bill shapes among adult songbirds in the presence of strong stabilizing or directional selection.

Change in offspring sex ratio over a very short season in Lincoln's Sparrows: the potential role of bill development

The sex ratios of offspring are targets of natural selection that can affect parental energy expenditure and fitness, adult sex ratios, and population dynamics. Parents may manipulate offspring sex ratios based on sex differences in potential reproductive success. In Lincoln’s Sparrows (Melospiza lincolnii), male bill shape is associated with the quality of songs, and song quality predicts female preferences in a reproductive context.Males and females that hatch later relative to brood mates or later in the breeding season tend to develop bill shapes that are, for males, associated with low-quality song. Because females do not sing and do not experience this selection pressure, we predicted that the sex of offspring produced late relative to their brood mates or relative to the season should be biased toward females. Using a molecular technique to sex nestlings, we found no effects of hatching order or any interaction between date of clutch initiation and hatching order on offspring sex. However, we found a seasonal decline in the proportion of male offspring, from approximately 0.8 at the beginning to 0.4 at the end of a clutch initiation season only 19 d in duration. To our knowledge, this is the shortest period over which the offspring sex ratio has been shown to change in a bird population. Moreover, these findings are consistent with the hypothesis that sex differences in the potential attractiveness of offspring ultimately influence offspring sex ratios.

Bernieridae (Aves: Passeriformes): a family-group name for the Malagasy sylvioid radiation

The island of Madagascar is a renowned hotspot for adaptive radiations. Madagascar has been separated from mainland Africa since the end of the Jurassic, and from India since the Late Cretaceous. This long isolation, combined with the island’s large size and relatively few dispersal events has resulted in an avifauna characterized by a low species count and high endemism: for instance, 80% of the breeding Malagasy songbirds (Passeriformes) are endemic (Hawkins & Goodman 2003). A first series of papers (Cibois et al. 1999, 2001; Fjeldsa et al. 1999) on the phylogeny of the Malagasy taxa traditionally classified as Timaliidae, Sylviidae and Pycnonotidae (all families included in the large sylvioid clade) showed that several of these passerines form an original radiation endemic to the island. Because these results were based solely on a single kind of molecular marker (mitochondrial DNA sequences), the authors refrained at that time from giving a name to this clade. More recently, other studies using nuclear markers as well (Beresford et al. 2005; Johansson et al. 2008a, 2008b) confirm the existence of this Malagasy sylvioid radiation. The species that comprise this group exhibit a great variety of bill shapes, wing and tail proportions, and tarsus lengths. This diversity in morphology is linked to varieties of habitat and prey favoured by these insectivorous forest dwellers (Schulenberg 2003). Thus the endemic Malagasy sylvioid clade rivals other island radiations, including the vangas of Madagascar and the finches of the Galapagos, in ecological and morphological diversity. Several authors were inclined to consider this group at the family level, using the name ‘Bernieridae’. To our knowledge the first study using this name was the book “The natural history of Madagascar”, edited by S. M. Goodman and J. Benstead in 2003, where the name ‘Bernieridae’ appeared in two chapters (in Tingle et al. (2003: p. 522) and Hawkins & Goodman (2003: p. 1036), although Schulenberg (2003: p. 1131) referred to the Malagasy "warblers" in his chapter on the radiations of passerine birds on Madagascar). An alternative spelling for the family-group name, ‘Bernieriidae’, can be found in several personal pages on the internet, but we have not found an occurrence of this in any publication, as defined in the International Code of Zoological Nomenclature (4th edition, 1999). The name ‘Bernieridae’ was later used in several journal articles (Chouteau & Fenosoa 2008; Fuchs et al. 2008; Johansson et al. 2008a, 2008b), however, none of these have introduced the family-group name ‘Bernieridae’ according to the provisions of the International Code of Zoological Nomenclature, i.e. the nominal taxon was not explicitly indicated as intentionally new (Article 16.1) and the type genus was not cited (Article 16.2). In the present paper, we therefore propose to rectify this situation by correctly introducing the family-group name for the Malagasy sylvioid radiation.

Oystercatchers' Bill Shapes as a Proxy for Diet Specialization: More Differentiation than Meets the Eye

Eurasian Oystercatchers Haematopus ostralegus ostralegus are a classic example of individual feeding specialization. Feeding specialization causes morphological differentiation in Oystercatchers' bill shapes due to varying degrees of abrasion associated with specific handling techniques for each prey species. Consequently, the Oystercatcher's bill shape has been used as a proxy for diet specialization, as it provides a quick and easy way to assess the diet choice of this marine top-predator. However, bill shapes of Oystercatchers are categorized visually in distinct types, while it has been argued that the relevant variation is continuous. Also, it is unclear how comparable the bill-shape classification is among studies and between the sexes and how universal bill shape-diet relationships are. Here we investigate the usefulness of bill-shape types as a proxy for diet choice in Oystercatchers, using four new and two published datasets. We show that quantitative bill-morphometrics provide no evidence that bill-shape types are discrete entities. Additionally, the dimensions of the same bill-shape type differ across studies. This difference is unlikely to be caused by methodology and might reflect subtle additional feeding specialization among birds with the same bill-shape type. Moreover, we show that the tip of the bill of males is typically 7% higher than that of females with the same bill-shape type. A higher — and probably stronger — bill tip in males may explain why males had more shellfish in their diet than females with the same bill-shape type. Finally, a literature-review shows that the exact bill shape-diet relationship differs between studies and the sexes. We conclude that the interpretation of bill-shape type as a proxy for diet choice in Oystercatchers is context dependent. We propose that quantitative bill dimensions are a better proxy for feeding specialization than bill-shape types.

Darwin’s Finches: Analysis of Beak Morphological Changes During Evolution: Figure 1.

INTRODUCTIONFinches of the Galápagos Islands were first described by Charles Darwin during his voyage on the HMS Beagle in 1835. Since then, through the subsequent work of many biologists, Darwin’s finches have become a classic textbook example of many important processes in evolution. Today, this group of birds continues to be a significant source of information on such processes as speciation, niche partitioning, morphological adaptation, and species ecology. The approximately 14 species of Darwin’s finches are closely related to one another and display a remarkable degree of diversity in bill shapes and sizes that are adapted for different food sources (e.g., seeds, insects, and even young leaves or blood from sea birds) in an otherwise scarce environment. For example, the deep and wide bills of the Ground Finches, one of the subgroups of Darwin’s finches, are used to feed on seeds, whereas the Cactus Finches use their elongated and narrow bills to probe cactus fruit and flowers. These differences in bill shapes are not due to their differential usage or other external factors; rather, the differences are genetically and developmentally regulated and can be observed and studied during embryogenesis. Therefore, Darwin’s finches are becoming a very useful non-model animal and avian system in which to investigate the molecular basis of morphological changes during evolution.

Highway Appropriations Bill Shapes Tribal Sovereignty: A Look at Oklahoma Tribes' Ability to Set Environmental Standards in Light of Recent Federal Legislation

Highway Appropriations Bill Shapes Tribal Sovereignty: A Look at Oklahoma Tribes' Ability to Set Environmental Standards in Light of Recent Federal Legislation

Osteologia craniana de Platalea ajaja (Linnaeus) (Aves, Ciconiiformes), comparada com outras espécies de Threskiornithidae

Platalea ajaja (Linnaeus, 1758) pertence Threskiornithidae (curicacas e afins e colhereiros), Threskiornithoidea, Ciconiiformes. Threskiornithidae (colhereiros, curicacas e afins) são subdivididos em dois grupos: Threskiornithinae que compreende curicacas e afins, caracteriza-se por seus representantes possuírem um bico longo, estreito e curvo, ao passo que Plataleinae inclui os colhereiros, que apresentam bico longo e achatado na ponta. O presente trabalho teve como objetivo descrever a osteologia craniana de P. ajaja (Plataleinae) e comparar com outras espécies pertencentes à Threskiornithinae. As espécies utilizadas para tal comparação foram: Mesembrinibis cayennensis (Gmelin, 1789), Phimosus infuscatus (Lichteinstein, 1823), Theristicus caudatus (Boddaert, 1783) e Plegadis chivi (Vieillot, 1817). Outras espécies pertencentes a ordem Ciconiiformes também foram utilizadas para comparação. A partir do presente estudo, observou-se que P. ajaja (Plataleinae) apresenta como características que a separa dos Threskiornithinae: 1) sutura frontonasal conspícua; 2) processo supra-orbital do osso lacrimal curto; 3) maxila superior achatada dorsoventralmente, sendo alargada na extremidade, tomando forma de uma colher; 4) narina curta e de forma oval; e 5) processo retroarticular curto. Entretanto, são necessários estudos osteológicos que contemplem as outras espécies da família, bem como um estudo filogenético do grupo para maior compreensão das relações existentes entre os Threskiornithidae.

Adaptive Geographical Variation in Bill Shape of Scrub Jays (Aphelocoma coerulescens)

The hypothesis of an adaptive basis to geographical variation in scrub jay bill shapes was tested using morphometric and phylogenetic approaches. Bill shapes of scrub jays include a short, hooked form and a long, pointed form, at least in females. The variation is closely associated with habitat use across the species' range: populations living in oak woodlands have short, hooked bills, whereas populations living in pinyon-juniper woodlands have long, pointed bills. The short, hooked form is apparently the primitive (pleisiomorphic) state in the species. The pointed form probably has been derived twice and lost once during the phylogenetic history of the species, each derivation being associated with invasion of pinyon-juniper woodlands and the loss with invasion of oak woodlands. Each bill form is most efficient at exploiting the foods present in the habitat with which it is associated, according to behavioral observations and functional arguments. Hence, the hypothesis that the variation is adaptive is ...

Structure and variation in the hindlimb musculature of the woodcreepers (Aves: Passeriformes: Dendrocolaptinae)

The Dendrocolaptinae (woodcreepers), a clade of neotropical passerine birds, form an adaptive radiation with a spectrum of body sizes and bill shapes. Woodcreepers are scansorial, climbing vertical tree trunks supported by their forward toes and stiffened tail. The hindlimb musculature was dissected and described for 42 of the 50 species representing all genera, and for 14 outgroup species. Structural, functional, developmental and evolutionary aspects of muscular variations are analysed. Woodcreepers have extensive ossification of leg tendons. There is intraspecific variation in the degree of ossification, and interspecific variation in the occurrence of ossification between muscles. Intraspecific variation in muscle structure was apportioned according to a published classification. Nine muscles showed variation of the minor, singular, mimicking and incongruous types, but explosive variation was lacking. Some muscles are more prone to variation than others. Ten muscles showed interspecific variations of four types, for which new terms are proposed: occurrence variations; attachment variations in origins and insertions; structural variations in size, shape, or fibre arrangement; and relational variations with other muscles. Variations in the presence of a muscle component did not occur. Discrimination of intraspecific variations from interspecific variations is discussed.

A comparison of interspecific differences in the morphology of external and internal feeding apparatus among North American Anatidae

We examined the relationship among bill shapes and gut morphology for 22 species of North American Anatidae. Bill shape was defined by nine bill measurements. Gut morphology was defined by the wet weights of empty ceca, small intestine, and gizzard. Interspecific differences in morphology were quantified through a canonical discriminant function analysis. Although the pattern of interspecific differences in the two sets of measurements showed some similarity (P < 0.001) this relationship was weak (R2 = 0.057). Species that were very similar or different in bill shape tended to be very similar or different in gut morphology. At any given intermediate distance of separation in either bill shape or gut morphology there was a wide range in separation in the other axis. We conclude that interspecific differences in both bill shape and gut morphology should be considered in studies of resource partitioning between closely related species at a particular time and location.

Dissimilar bill shapes in new world tropical versus temperate forest foliage-gleaning birds.

The bill shape of foliage-gleaning birds in temperate and tropical new world forests is dissimilar. Tropical species have longer and narrower bills than their temperate zone counterparts. In addition, their bills are longer for a given body size. These differences cannot be readily explained as phylogenetic artifacts. I suggest that the distinct bill morphology of the two assemblages is determined by the type of insects that comprise the largest size classes of potential prey. These large insects are particularly important since they generally comprise the bulk of the nestling diet for insectivorous birds. In tropical forests Orthoptera are probably the most abundant large soft-bodied arthropods; they form an important resource for foliage-gleaning birds during the breeding (rainy) seasons. Most temperate zone foliage-gleaning birds rely almost entirely upon caterpillars when breeding. Long, narrow bills are thought to close more rapidly than shorter, broader bills. These long, "fast" bills may be required to efficiently harvest active Orthoptera. Migrant warblers may face morphological constraints from breeding successfully in lowland tropical forests. While the short-billed temperate zone birds can survive the tropical dry season by foraging on small arthropods, they may be inefficient at handling large Orthoptera to feed to nestlings.