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opencc-zeroJan 2024View details →

Ecological and Morphological Correlates of Acuity in Birds

Birds use their visual systems for a variety of important tasks, such as foraging and predator detection, that require them to resolve an image. However, visual acuity (the ability to perceive spatial detail) varies by two orders of magnitude across birds. Prior studies indicate that eye size and aspects of a species' ecology may drive variation in acuity, but these studies have been restricted to small numbers of species. We used a literature review to gather data on acuity measured either behaviorally or anatomically for 94 species from 38 families. We then examined how acuity varies in relation to (1) eye size, (2) habitat spatial complexity, (3) habitat light level, (4) diet composition, (5) prey mobility, and (6) foraging mode. A phylogenetically-controlled model including all of the above factors as predictors indicated that eye size, habitat spatial complexity, light level, and diet composition are significant predictors of acuity. Examining each ecological variable in turn revealed that acuity is lower in species that inhabit spatially complex, vegetative habitats, and higher in species whose diet comprises vertebrates or scavenged food. Together, our results suggest that the need to detect important objects from far away—such as predators for species that live in open habitats, and food items for species that forage on vertebrate and scavenged prey—has likely been a key driver of higher acuity in some species, helping to elucidate how visual capabilities may be adapted to an animal's visual needs.

FIGURE 4 in AVONET: morphological, ecological and geographical data for all birds

FIGURE 4 Geographical distribution of morphological data sampling. (a) Location of collections sampled (n = 78 museums or scientific collections in 31 countries), with the number of specimens per collection indicated by bubble size (excluding seven specimens from unknown museums). Sampling of live-caught and released individuals (n = 14,177) is not shown. (b) The number of individual birds sampled from each of 206 administrative units (181 countries), combining museum and field sampling (removing cases not assignable to administrative units). Darker colours indicate a larger number of specimens; specimens lacking precise information on the country of origin (n = 12,775) are not included. (c) The completeness of species sampling in each 100 km grid cell. Colours show the proportion of species present in that cell with specimens sampled from the same country in which the cell is located; warmer colours indicate higher proportions. Species presence was mapped as the portion of the species range occurring within the country, because the specimen is unlikely to have originated from outside the natural range

FIGURE 2 in AVONET: morphological, ecological and geographical data for all birds

FIGURE 2 Diagram of linear measurements of avian morphology presented in AVONET. (a) Resident frugivorous tropical passerine (fiery-capped manakin,Machaeropterus pyrocephalus) showing four beak measurements: (1) beak length measured from tip to skull along the culmen; (2) beak length measured from the tip to the anterior edge of the nares; (3) beak depth; (4) beak width. (b) Insectivorous migratory temperate-zone passerine (redwing, Turdus iliacus) showing five body measurements: (5) tarsus length; (6) wing length from carpal joint to wingtip measured on the unflattened wing; (7) secondary length from carpal joint to tip of the outermost secondary; (8) Kipp's distance, measured directly or calculated as wing length minus first-secondary length; (9) tail length. Protocols for measuring these traits are provided in Supplementary material. AVONET also includes body mass, and Hand-wing index (calculated from 6 to 8), making 11 traits in total. Illustration by Richard Johnson

FIGURE 1 in AVONET: morphological, ecological and geographical data for all birds

FIGURE 1 The sampling of avian morphological traits over time. The number of species (above x axis) and the number of specimens (below x axis) measured for landmark studies along with their year of publication is indicated by the vertical bars. Each bar indicates the maximum number of species and specimens measured for any trait. The number of traits in each study is represented by circle sizes (continuous from 1 to 15, with examples shown in the legend). Studies openly providing raw trait data are indicated in black. AVONET contains the raw specimen-level data for Pigot et al. (2020), along with substantial expansion in coverage of both species and specimens-per-species. To provide historical context, coloured time periods correspond roughly to interest in 'ecomorphology' (blue) and 'functional traits' (red). Citations for studies not used in the main text are provided in the Supplementary Material

FIGURE 6 in AVONET: morphological, ecological and geographical data for all birds

FIGURE 6 Species-level variation in avian functional traits in relation to geography and lifestyle. Hand-wing index (wing elongation) peaks towards high latitudes (a), and in species with aquatic and aerial lifestyles (b); relative tarsus length peaks at mid-latitudes and non-forest regions (c), and in species with terrestrial lifestyles (d); relative beak length peaks in the tropics, including rainforests (e), and in nectar feeders and aquatic predators (f). For maps, median trait values were calculated for 18,709 grid-cell assemblages worldwide. Darker colours indicate larger trait values. Assemblages were delimited by extracting species native resident or breeding distributions (n = 10,964 species for which both trait and geographical range data are available) onto an equal area grid with a cell resolution of ~100 km (Behrmann projection). Relative beak and tarsus length are the residuals of a linear regression of log-transformed tarsus and beak length (mm) against log-transformed body mass (grams). Species in (b,d) are classified according to primary lifestyle (predominant locomotory niche; insessorial = perching lifestyle). Species in (f) are classified according to primary diet following Pigot et al. (2020). Sample sizes (b,d,f) are numbers of species in each category

FIGURE 3 Morphological trait sampling for all bird families. AVONET contains 718,662 in AVONET: morphological, ecological and geographical data for all birds

FIGURE 3 Morphological trait sampling for all bird families. AVONET contains 718,662 individual trait measurements, all of which are used to calculate species averages. However, sampling per species varies across families depending on taxonomy. Upper phylogram shows sampling under BirdLife International (11,009 species in 243 families). Families where sampling completeness is below 75% indicated by lighter shading. Most families with lower sampling are species poor (numbers in black circles show species richness). Lower panels show that sampling improves under more conservative taxonomic treatments of eBird (10,661 species in 249 families) and BirdTree (9993 species in 194 families). Coloured bars indicate the proportion of species in each family measured to different levels of completeness. 'Complete set' means a full set of all 9 core morphological traits (not necessarily from the same individual). 'Individuals' means any individual bird with one or more traits measured

FIGURE 5 AVONET presents raw morphological data for 90,020 in AVONET: morphological, ecological and geographical data for all birds

FIGURE 5 AVONET presents raw morphological data for 90,020 individual birds at an average of 8.1–9.0 individuals per species (varying by taxonomy), providing a foundation for a new generation of studies investigating or accounting for intraspecific variance. This figure illustrates how variance is partitioned for a key morphological trait (beak length). Left-hand panels show that most variance is explained at higher taxonomic levels (orders, family and species), whereas intraspecific (individual) variation is contrastingly low, supporting the use of species averages in comparative studies. Curves are normal distributions based on SD; percentages (%) show proportion of variance at each level. Right-hand panels show beak length variance within families and within species (restricting to families with>5 species and species with>5 individuals measured; note different axis scales in upper and lower panel). Sequential ranks show a 'hockey-stick' distribution with examples of the most extreme outlier family (Scolopacidae) illustrated. Extreme within-species values for beak variance may reflect polymorphism or, in some cases, measurement error

opencc-zeroSep 2019View details →

Data from: Ecology and evolution of blood oxygen-carrying capacity in birds

Blood oxygen-carrying capacity is one of important determinants of oxygen amounts supplied to the tissues per unit time and plays a key role in oxidative metabolism. In wild vertebrates, blood oxygen-carrying capacity is most commonly measured with the total blood haemoglobin concentration (Hb) and haematocrit (Hct), which is the volume percentage of red blood cells in blood. Here, I used published estimates of avian Hb and Hct (nearly one thousand estimates from 300 species) to examine macroevolutionary patterns in blood oxygen-carrying capacity of blood in birds. Phylogenetically-informed comparative analysis indicated that blood oxygen-carrying capacity was primarily determined by species distribution (latitude and elevation) and morphological constraints (body mass). I found little support for the effect of life history components on blood oxygen-carrying capacity, except for a positive association of Hct with clutch size. Hb was also positively associated with diving behaviour, but I found no effect of migratoriness on either Hb or Hct. Fluctuating selection was identified as the major force shaping the evolution of blood oxygen-carrying capacity. The results offer novel insights into the evolution of Hb and Hct in birds, as well as they provide a general, phylogenetically-robust support for some long-standing hypotheses in avian ecophysiology.

opencc-by-4.0Jul 2024View details →

Raw data for: Spatial and temporal variation in farmland bird nesting ecology: Implications for effective Corn Bunting Emberiza calandra conservation

These are raw data accompanying the study "Spatial and temporal variation in farmland bird nesting ecology: Implications for effective Corn Bunting Emberiza calandra conservation". All information on data origin, data analysis, and derived implications will be available with the original publiation.

opencc-zeroJul 2023View details →

Data from: An environmental habitat gradient and within-habitat segregation enable co-existence of ecologically similar bird species

Niche theory predicts that ecologically similar species can co-exist through multidimensional niche partitioning. However, due to the challenges of accounting for both abiotic and biotic processes in ecological niche modelling, the underlying mechanisms that facilitate co-existence of competing species are poorly understood. In this study, we evaluated potential mechanisms underlying the co-existence of ecologically similar bird species in a biodiversity-rich transboundary montane forest in east-central Africa by computing niche overlap indices along an environmental elevation gradient, diet, forest strata, activity patterns, and within-habitat segregation across horizontal space. We found strong support for abiotic environmental habitat niche partitioning, with 55% of species pairs having separate elevation niches. For the remaining species pairs that exhibited similar elevation niches, we found that within-habitat segregation across horizontal space and to a lesser extent vertical forest strata provided the most likely mechanisms of species co-existence. Co-existence of ecologically similar species within a highly diverse montane forest was determined primarily by abiotic factors (e.g., environmental elevation gradient) that characterize the Grinnellian niche and secondarily by biotic factors (e.g., vertical and horizontal segregation within habitats) that describe the Eltonian niche. Thus, partitioning across multiple levels of spatial organization is a key mechanism of co-existence in diverse communities.

opencc-by-4.0May 2022View details →

Figure 1 in Perspectives and challenges on isotopic ecology of terrestrial birds in Brazil

Figure 1. Flowchart of potential study themes (in bold) to be developed in isotopic ecology with terrestrial birds in Brazil. Each theme branches into several sub-themes that can be explored (first boxes below the themes) and the methods and approaches that can be employed to develop the studies (within the dashed boxes). Many methods and approaches are interchangeable among themes and subthemes (represented by the horizontal arrow). In addition, the shortcomings of stable isotope ecology that should be considered before or during the development of the studies.

opencc-zeroSep 2023View details →

Data from: Species-specific ecological traits, phylogeny, and geography underpin vulnerability to population declines for North American birds

Species declines and extinctions characterize the Anthropocene. Determining species vulnerability to decline, and where and how to mitigate threats, are paramount for effective conservation. We hypothesized that species with shared ecological traits also share threats, and therefore may experience similar population trends. Here, we used a Bayesian modeling framework to test whether phylogeny, geography, and 22 ecological traits predict regional population trends for 380 North American bird species. Groups like blackbirds, warblers, and shorebirds, as well as species occupying Bird Conservation Regions at more extreme latitudes in North America, exhibited negative population trends, while groups such as ducks, raptors, and waders, as well as species occupying more inland Bird Conservation Regions, exhibited positive trends. Specifically, we found that in addition to phylogeny and breeding geography, multiple ecological traits contributed to explaining variation in regional population trends for North American birds. Furthermore, we found that regional trends and the relative effects of migration distance, phylogeny, and geography differ between shorebirds, songbirds, and waterbirds. Our work provides evidence that multiple ecological traits correlate with North American bird population trends, but that the individual effects of these ecological traits in predicting population trends often vary between different groups of birds. Moreover, our results reinforce the notion that variation in avian population trends is controlled by more than phylogeny and geography, where closely-related species within one region can show unique population trends due to differences in their ecological traits. We recommend that regional conservation plans, i.e. one-size-fits-all plans, be implemented only for bird groups with population trends under strong phylogenetic or geographic controls. We underscore the need to develop species-specific research and management strategies for other groups, like songbirds, that exhibit high variation in their population trends and are influenced by multiple ecological traits.

publicJan 2024View details →

Ecological and Morphological Correlates of Acuity in Birds

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publicJul 2023View details →

Data from: An environmental habitat gradient and within-habitat segregation enable co-existence of ecologically similar bird species

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publicSep 2023View details →

Data from: Species-specific ecological traits, phylogeny, and geography underpin vulnerability to population declines for North American birds

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