Genome size and developmental parameters in the homeothermic vertebrates.

Although unrelated to any intuitive notions of organismal complexity, haploid genome sizes (C values) are correlated with a variety of cellular and organismal parameters in different taxa. In some cases, these relationships are universal--notably, genome size correlates positively with cell size in each of the vertebrate classes. Other relationships are apparently relevant only in particular groups. For example, although genome size is inversely correlated with metabolic rate in both mammals and birds, no such relationship is found in amphibians. More recently, it has been suggested that developmental rate and (or) longevity are related to genome size in birds. In the present study, a large dataset was used to examine possible relationships between genome size and various developmental parameters in both birds and mammals. In neither group does development appear to be of relevance to genome size evolution (except perhaps indirectly in birds through the intermediation of body size and (or) within the rodents), a situation very different from that found in amphibians. These findings make it clear that genome size evolution cannot be understood without reference to the particular biology of the organisms under study.     

An allometric study of pulmonary morphometric parameters in birds, with mammalian comparisons

Comprehensive pulmonary morphometric data from 42 species of birds representing ten orders were compared with those of other vertebrates, especially mammals, relating the comparisons to the varying biological needs of these avian taxa. The total lung volume was strongly correlated with body mass. The volume density of the exchange tissue was lowest in the charadriiform and anseriform species and highest in the piciform, cuculiform and passeriform species. The surface area of the blood-gas (tissue) barrier, the volume of the pulmonary capillary blood and the total morphometric pulmonary diffusing capacity were all strongly correlated with body mass. The harmonic mean thickness of both the blood-gas (tissue) barrier and the plasma layer were weakly correlated with body mass. The mass-specific surface area of the blood-gas (tissue) barrier (surface area per gram body mass) and the surface density of the blood-gas (tissue) barrier (i.e. its surface area per unit volume of exchange tissue) were inversely correlated (though weakly) with body mass. The passeriform species exhibited outstanding pulmonary morphometric adaptations leading to a high specific total diffusing capacity per gram body mass, consistent with the comparatively small size and energetic mode of life which typify passeriform birds. The relatively inactive, ground-dwelling domestic fowl (Gallus gallus) had the lowest pulmonary diffusing capacity per gram body mass. The specific total lung volume is about 27% smaller in birds than in mammals but the specific surface area of the blood-gas (tissue) barrier is about 15% greater in birds. The ratio of the surface area of the tissue barrier to the volume of the exchange tissue was also much greater in the birds (170-305%). The harmonic mean thickness of the tissue barrier was 56-67% less in the birds, but that of the plasma layer was about 66% greater in the birds. The pulmonary capillary blood volume was also greater (22%) in the birds. Except for the thickness of the plasma layer, these morphometric parameters all favour the gas exchange capacity of birds. Consequently, the total specific mean morphometric pulmonary diffusing capacity for oxygen was estimated to be about 22% greater in birds than in mammals of similar body mass. This estimate was obtained by employing oxygen permeation constants for mammalian tissue, plasma and erythrocytes, as avian constants were not then available.(ABSTRACT TRUNCATED AT 400 WORDS)     

Examining the Prey Mass of Terrestrial and Aquatic Carnivorous Mammals: Minimum,Maximum and Range

Predator-prey body mass relationships are a vital part of food webs across ecosystems and provide key information for predicting the susceptibility of carnivore populations to extinction. Despite this, there has been limited research on the minimum and maximum prey size of mammalian carnivores. Without information on large-scale patterns of prey mass, we limit our understanding of predation pressure, trophic cascades and susceptibility of carnivores to decreasing prey populations. The majority of studies that examine predator-prey body mass relationships focus on either a single or a subset of mammalian species, which limits the strength of our models as well as their broader application. We examine the relationship between predator body mass and the minimum, maximum and range of their prey''s body mass across 108 mammalian carnivores, from weasels to baleen whales (Carnivora and Cetacea). We test whether mammals show a positive relationship between prey and predator body mass, as in reptiles and birds, as well as examine how environment (aquatic and terrestrial) and phylogenetic relatedness play a role in this relationship. We found that phylogenetic relatedness is a strong driver of predator-prey mass patterns in carnivorous mammals and accounts for a higher proportion of variance compared with the biological drivers of body mass and environment. We show a positive predator-prey body mass pattern for terrestrial mammals as found in reptiles and birds, but no relationship for aquatic mammals. Our results will benefit our understanding of trophic interactions, the susceptibility of carnivores to population declines and the role of carnivores within ecosystems.     

The scaling and temperature dependence of vertebrate metabolism

Body size and temperature are primary determinants of metabolic rate, and the standard metabolic rate (SMR) of animals ranging in size from unicells to mammals has been thought to be proportional to body mass (M) raised to the power of three-quarters for over 40 years. However, recent evidence from rigorously selected datasets suggests that this is not the case for birds and mammals. To determine whether the influence of body mass on the metabolic rate of vertebrates is indeed universal, we compiled SMR measurements for 938 species spanning six orders of magnitude variation in mass. When normalized to a common temperature of 38 degrees C, the SMR scaling exponents of fish, amphibians, reptiles, birds and mammals are significantly heterogeneous. This suggests both that there is no universal metabolic allometry and that models that attempt to explain only quarter-power scaling of metabolic rate are unlikely to succeed.     

Relationship between body size, Na+-K+-ATPase activity, and membrane lipid composition in mammal and bird kidney

We investigated the relationship between body size, Na(+)-K(+)-ATPase molecular activity, and membrane lipid composition in the kidney of five mammalian and eight avian species ranging from 30-g mice to 280-kg cattle and 13-g zebra finches to 35-kg emus, respectively. Na(+)-K(+)-ATPase activity was found to be higher in the smaller species of both groups. In small mammals, the higher Na(+)-K(+)-ATPase activity was primarily the result of an increase in the molecular activity (turnover rate) of individual enzymes, whereas in small birds the higher Na(+)-K(+)-ATPase activity was the result of an increased enzyme concentration. Phospholipids from both mammals and birds contained a relatively constant percentage of unsaturated fatty acids; however, phospholipids from the smaller species were generally more polyunsaturated, and a complementary significant allometric increase in monounsaturate content was observed in the larger species. In particular, the relative content of the highly polyunsaturated docosahexaenoic acid [22:6(n-3)] displayed the greatest variation with body mass, scaling with allometric exponents of -0.21 and -0.26 in the mammals and birds, respectively. This allometric variation in fatty acid composition was correlated with Na(+)-K(+)-ATPase molecular activity in mammals, whereas in birds molecular activity only correlated with membrane cholesterol content. These relationships are discussed with respect to the metabolic intensity of different-sized animals.     

Scaling of Na+,K+-ATPase molecular activity and membrane fatty acid composition in mammalian and avian hearts

We have examined Na(+),K(+)-ATPase molecular activity and membrane fatty acid composition in the heart of six mammalian and eight avian species ranging in size from 30 g in mice to 280 kg in cattle and 13 g in zebra finches to 35 kg in emus, respectively. Na(+),K(+)-ATPase activity scaled negatively with body mass in both mammals and birds. In small mammals, the elevated enzyme activity was related to allometric changes in both the concentration and molecular activity (turnover rate) of Na(+),K(+)-ATPase enzymes, while in small birds, higher Na(+),K(+)-ATPase activity appeared to result primarily from an increased molecular activity of individual enzymes. The unsaturation index of cardiac phospholipids scaled negatively with body mass in both groups, while a significant allometric increase in monounsaturate content was observed in the larger mammals and birds. In particular, the relative content of the highly polyunsaturated docosahexaenoic acid (22:6n-3) displayed the greatest variation, scaling negatively with body mass and varying greater than 40-fold in both mammals and birds. Membrane fatty acid profile was correlated with Na(+),K(+)-ATPase molecular activity in both mammals and birds, suggesting a potential association between membrane lipid composition and the activity of membrane-bound enzymes in the hearts of endotherms.     

Morphometrics of the avian small intestine compared with that of nonflying mammals: a phylogenetic approach

Flying animals may experience a selective constraint on gut volume because the energetic cost of flight increases and maneuverability decreases with greater digesta load. The small intestine is the primary site of absorption of most nutrients (e.g., carbohydrates, proteins, fat) in both birds and mammals. Therefore, we used a phylogenetically informed approach to compare small intestine morphometric measurements of birds with those of nonflying mammals and to test for effects of diet within each clade. We also compared the fit of nonphylogenetic and phylogenetic models to test for phylogenetic signal after accounting for effects of body mass, clade, and/or diet. We provide a new MATLAB program (Regressionv2.m) that facilitates a flexible model-fitting approach in comparative studies. As compared with nonflying mammals, birds had 51% less nominal small intestine surface area (area of a smooth bore tube) and 32% less volume. For animals <365 g in body mass, birds also had significantly shorter small intestines (20%-33% shorter, depending on body mass). Diet was also a significant factor explaining variation in small intestine nominal surface area of both birds and nonflying mammals, small intestine mass of mammals, and small intestine volume of both birds and nonflying mammals. On the basis of the phylogenetic trees used in our analyses, small intestine length and nominal surface area exhibited statistically significant phylogenetic signal in birds but not in mammals. Thus, for birds, related species tended to be similar in small intestine length and nominal surface area, even after accounting for relations with body mass and diet. A reduced small intestine in birds may decrease the capacity for breakdown and active absorption of nutrients. Birds do not seem to compensate for reduced digestive and absorptive capacity via a longer gut retention time of food, but we found some evidence that birds have an increased mucosal surface area via a greater villus area, although not enough to compensate for reduced nominal surface area. We predict that without increased rate of enzyme hydrolysis and/or mediated transport and without increased passive absorption of water-soluble nutrients, birds may operate with a reduced digestive capacity, compared with that of nonflying mammals, to meet an increase in metabolic needs (i.e., a reduced spare capacity).     

Variability and size in mammals and birds

Body size, its variability, and their ecological correlates have long been important topics in evolutionary biology. Yet, the question of whether there is a general relationship between size and size-relative variability has not previously been addressed. Through an analysis of body-mass and length measurements from 65 074 individuals from 351 mammalian species, we show that size-relative variability increases significantly with mean species body size. Analysis of mean body mass and standard deviations for 237 species of birds revealed the same pattern. We present three plausible alternatives explanations and eliminate several others. Of these, the hypothesis that the increase in size-relative variability with mean body mass is related to the scaling of body mass components is most strongly supported. In effect, larger mammals and birds are more variable because their body mass is composed to greater relative degree of components with higher intrinsic variability (bone, fat, and muscle). In contrast, smaller mammals and birds have lower body mass variability because they are composed to a greater relative extent of components (viscera and nervous system) in which size variation is more highly constrained by energetic and functional factors.     

A global assessment of Bergmann's rule in mammals and birds

Bergmann's rule states that endotherms have a large body size in high latitudes and cold climates. However, previous empirical studies have reported mixed evidence on the relationships between body size and latitude, raising the question of why some clades of endotherms follow Bergmann's rule, whereas others do not. Here, we synthesized the interspecific relationships between body size and latitude among 16,187 endothermic species (5422 mammals and 10,765 birds) using Bayesian phylogenetic generalized linear mixed models to examine the strength and magnitude of Bergmann's rule. We further assessed the effect of biological and ecological factors (i.e., body mass categories, dietary guild, winter activity, habitat openness, and climate zone) on the variations in the body mass–latitude relationships by adding an interaction term in the models. Our results revealed a generally weak but significant adherence to Bergmann's rule among all endotherms at the global scale. Despite taxonomic variation in the strength of Bergmann's rule, the body mass of species within most animal orders showed an increasing trend toward high latitudes. Generally, large-bodied, temperate species, non-hibernating mammals, and migratory and open-habitat birds tend to conform to Bergmann's rule more than their relatives do. Our results suggest that whether Bergmann's rule applies to a particular taxon is mediated by not only geographic and biological features, but also potential alternate strategies that species might have for thermoregulation. Future studies could explore the potential of integrating comprehensive trait data into phylogenetic comparative analysis to re-assess the classic ecogeographic rules on a global scale.     

Spleen mass as a measure of immune strength in mammals

• 1 In studies of birds and their pathogens, spleen size has frequently been used to make inferences about immune system strength. However, the use of spleen size in mammals is more complicated because, in addition to having an immune function, the mammalian spleen is also a reservoir for red blood cells.
• 2 To assess the reliability of mammalian spleen mass as an indicator of immune activity, we quantified the white and red pulp mass by histology of spleens from shot red deer Cervus elaphus. We then analysed the relationships among spleen mass, the amounts of white and red pulp, and the deer's body condition relative to faecal counts of the nematode parasite Elaphostrongylus cervi.
• 3 White and red pulp mass were positively correlated so that an increase in spleen mass was a positive function of both components of the spleen. In male deer, which had significantly lower body condition and higher parasite loads than females, parasite counts were negatively correlated with spleen mass, white pulp mass, and red pulp mass.
• 4 Our findings suggest that (i) spleen mass in shot red deer is a reliable measure of white and red pulp content; and (ii) when looking at the red deer life history, which is greatly influenced by sex of the deer, splenic mass and white pulp mass could be used as reflections of immune system strength.
• 5 Future studies of mammalian spleens can contribute to the understanding of evolved strategies of immune response investment in mammals. However, determination of the white and red pulp spleen components using various sampling methods must be made prior to their application.

     

Unveiling the environmental drivers of intraspecific body size variation in terrestrial vertebrates

Aim

Whether intraspecific spatial patterns in body size are generalizable across species remains contentious, as well as the mechanisms underlying these patterns. Here we test several hypotheses explaining within-species body size variation in terrestrial vertebrates including the heat balance, seasonality, resource availability and water conservation hypotheses for ectotherms, and the heat conservation, heat dissipation, starvation resistance and resource availability hypotheses for endotherms.

Location

Global.

Time period

1970–2016.

Major taxa studied

Amphibians, reptiles, birds and mammals.

Methods

We collected 235,905 body size records for 2,229 species (amphibians = 36; reptiles = 81; birds = 1,545; mammals = 567) and performed a phylogenetic meta-analysis of intraspecific correlations between body size and environmental variables. We further tested whether correlations differ between migratory and non-migratory bird and mammal species, and between thermoregulating and thermoconforming ectotherms.

Results

For bird species, smaller intraspecific body size was associated with higher mean and maximum temperatures and lower resource seasonality. Size–environment relationships followed a similar pattern in resident and migratory birds, but the effect of resource availability on body size was slightly positive only for non-migratory birds. For mammals, we found that intraspecific body size was smaller with lower resource availability and seasonality, with this pattern being more evident in sedentary than migratory species. No clear size–environment relationships were found for reptiles and amphibians.

Main conclusions

Within-species body size variation across endotherms is explained by disparate underlying mechanisms for birds and mammals. Heat conservation (Bergmann's rule) and heat dissipation are the dominant processes explaining biogeographic intraspecific body size variation in birds, whereas in mammals, body size clines are mostly explained by the starvation resistance and resource availability hypotheses. Our findings contribute to a better understanding of the mechanisms behind species adaptations to the environment across their geographic distributions.     

The principle of laplace and scaling of ventricular wall stress and blood pressure in mammals and birds

Maximum left ventricular wall stress is calculated at end-diastolic volume and systemic arterial diastolic blood pressure, according to a thick-walled model for the principle of Laplace. Stress is independent of body mass and averages 13.9 kPa (+/-2.3; 95% confidence interval) in 24 species of mammals weighing 0.025-4,000 kg and 15.5 kPa (+/-4.7) in 12 birds weighing 0.014-110 kg. Birds have higher arterial blood pressures and larger hearts than mammals. Systolic and diastolic arterial blood pressures increase with body mass according to M(0.05) in mammals, and heart mass increases according to M(1.06) in the same species, further supporting the principle. However, blood pressure in birds is independent of body mass, and heart mass scales isometrically. End-diastolic stress values, calculated according to Laplace, are about one-third of peak stresses recorded in isolated mammalian myocardial preparations.     

An allometric comparison of the mitochondria of mammalian and reptilian tissues: The implications for the evolution of endothermy

Summary The effects of body size and phylogeny on metabolic capacities were examined by comparing the mitochondrial capacities of 6 mammalian and 4 reptilian species representing 100-fold body weight ranges. The mammals examined included 3 eutherian, 2 marsupial and a monotreme species and the reptiles 2 saurian, 1 crocodilian and 1 testudine species. The tissues examined were liver, kidney, brain, heart, lung and skeletal muscle. Allometric equations were derived for tissue weights, mitochondrial volume densities, internal mitochondrial membrane surface area densities, tissue mitochondrial membrane surface areas both per gram and per total tissue and summated tissue mitochondrial membrane surface areas. For the mammals and reptiles studied a 100% increase in body size resulted in average increases of 68% in internal organ size and 107% in skeletal muscle mass. Similarly, total organ mitochondrial membrane surface areas increase in mammals and reptiles by an average 54% and for skeletal muscle by an average 96%. These values are similar to increases in standard (54 and 71%) and maximum (73 and 77%) organismal metabolism values found by other authors for mammals and reptiles respectively. Although the allometric exponents (or rates of change with increasing body size) of the mitochondrial parameters in mammals and reptiles are statistically the same, in general the total amount of mitochondrial membrane surface area in the mammalian tissues are four times greater than found in the reptilian tissues. These differences were not the result of any single ‘quantum’ factor but are the result of the mammals having relatively larger tissues with a greater proportion of their volume occupied by mitochondria and to a lesser extent increases in the internal mitochondrial membrane surface area densities. Mitochondrial volume density from this present study would appear to be the major factor involved in changing weight specific metabolism of tissues both as a result of changes in body size and in the evolution of endothermy in mammals from reptiles.     

The limits to population density in birds and mammals

We address two fundamental ecological questions: what are the limits to animal population density and what determines those limits? We develop simple alternative models to predict population limits in relation to body mass. A model assuming that within‐species area use increases with the square of daily travel distance broadly predicts the scaling of empirical extremes of minimum density across birds and mammals. Consistent with model predictions, the estimated density range for a given mass, ‘population scope’, is greater for birds than for mammals. However, unlike mammals and carnivorous birds, expected broad relationships between body mass and density extremes are not supported by data on herbivorous and omnivorous birds. Our results suggest that simple constraints on mobility and energy use/supply are major determinants of the scaling of density limits, but further understanding of interactions between dietary constraints and density limits are needed to predict future wildlife population responses to anthropogenic threats.     

Seasonal and sex-specific prey composition of black-footed catsFelis nigripes

During a 6-year field study on the game farm ‘Benfontein’ in the central Republic of South Africa 1725 prey items were observed consumed by 17 free-ranging habituated black-footed catsFelis nigripes Burchell, 1824. Average prey size was 24.1 g. Eight males fed on significantly larger prey (27.9 g) than 9 females (20.8 g). Fifty-four prey species were classified by their average mass into 8 different size classes, 3 for mammals, 3 for birds, 1 for amphibians/reptiles, and 1 for invertebrates. Small mammals (5–40 g) constituted the most important prey class (39%) of total prey biomass followed by larger mammals (>100 g; 17%) and small birds (<40 g; 16%). Mammals and birds pooled comprised 72% and 26% of total prey biomass, respectively, whereas invertebrates and amphibians/reptiles combined constituted just 2% of total prey mass consumed. Three seasons of 4-months duration were recognized. Heterotherm prey items were unavailable during winter, when larger birds and mammals (> 100 g) were mainly consumed. Small rodents like the large-eared mouseMalacothrix typica, captured 595 times by both sexes, were particularly important during the reproductive season for females with kittens. Male black-footed cats showed less variation between prey size classes consumed among climatic seasons. This sex-specific difference in prey size consumption may help to reduce intra-specific competition.     

Body cavities in fishes

Four types of body cavity arrangement were found in 20 species of fish (see Materials and Methods). The body cavities of fishes were also compared with those of mammals and birds. It was concluded that higher vertebrates utilized only the Tinca type for their evolution, while the other types were dead-end evolutionary forms which terminated at fish level, or possibly with amphibians and reptiles. The necessary research in these groups still remains to be done.     

Why elephant have trunks and giraffe long tongues: how plants shape large herbivore mouth morphology

We investigated whether mass and morphological spatial patterns in plants possibly induced the development of enlarged soft mouth parts in especially megaherbivores. We used power functions and geometric principles to explore allometric relationships of both morphological and foraging characteristics of mammalian herbivores in the South African savannah, covering a body size range of more than three orders magnitude. Our results show that, although intradental mouth volume scaled to a power slightly less than one to body mass, actual bite volume, as measured in the field, scaled to body mass with a factor closer to 1.75. However, when including the volume added to intradental mouth volume by soft mouth parts, such as tongue and lips (or trunks in elephant), mouth volume scaled linearly with actual bite volume and in a similar fashion as actual bite volume to body size. Bite mass and bite leaf mass scaled linearly with body size. We conclude that these scaling relationships indicate that large herbivores use their enlarged soft mouth parts to not only increase bite volume and thereby bite mass, but also select soft plant parts and thereby increase the leaf mass fraction per bite.     

Causes and consequences of variation in offspring body mass: meta‐analyses in birds and mammals

Early survival is highly variable and strongly influences observed population growth rates in most vertebrate populations. One of the major potential drivers of survival variation among juveniles is body mass. Heavy juveniles are better fed and have greater body reserves, and are thus assumed to survive better than light individuals. In spite of this, some studies have failed to detect an influence of body mass on offspring survival, questioning whether offspring body mass does indeed consistently influence juvenile survival, or whether this occurs in particular species/environments. Furthermore, the causes for variation in offspring mass are poorly understood, although maternal mass has often been reported to play a crucial role. To understand why offspring differ in body mass, and how this influences juvenile survival, we performed phylogenetically corrected meta‐analyses of both the relationship between offspring body mass and offspring survival in birds and mammals and the relationship between maternal mass and offspring mass in mammals. We found strong support for an overall positive effect of offspring body mass on survival, with a more pronounced influence in mammals than in birds. An increase of one standard deviation of body mass increased the odds of offspring survival by 71% in mammals and by 44% in birds. A cost of being too fat in birds in terms of flight performance might explain why body mass is a less reliable predictor of offspring survival in birds. We then looked for moderators explaining the among‐study differences reported in the intensity of this relationship. Surprisingly, sex did not influence the intensity of the offspring mass–survival relationship and phylogeny only accounted for a small proportion of observed variation in the intensity of that relationship. Among the potential factors that might affect the relationship between mass and survival in juveniles, only environmental conditions was influential in mammals. Offspring survival was most strongly influenced by body mass in captive populations and wild populations in the absence of predation. We also found support for the expected positive effect of maternal mass on offspring mass in mammals (r_pearson = 0.387). As body mass is a strong predictor of early survival, we expected heavier mothers to allocate more to their offspring, leading them to be heavier and so to have a higher survival. However, none of the potential factors we tested for variation in the maternal mass–offspring mass relationship had a detectable influence. Further studies should focus on linking these two relationships to determine whether a strong effect of offspring size on early survival is associated with a high correlation coefficient between maternal mass and offspring mass.     

The effect of body size and habitat on the evolution of alarm vocalizations in rodents

When confronted with a predator, many mammalian species emit vocalizations known as alarm calls. Vocal structure variation results from the interactive effects of different selective pressures and constraints affecting their production, transmission, and detection. Body size is an important morphological constraint influencing the lowest frequencies that an organism can produce. The acoustic environment influences signal degradation; low frequencies should be favoured in dense forests compared to more open habitats (i.e. the ‘acoustic adaptation hypothesis’). Such hypotheses have been mainly examined in birds, whereas the proximate and ultimate factors affecting vocalizations in nonprimate mammals have received less attention. In the present study, we investigated the relationships between the frequency of alarm calls, body mass, and habitat in 65 species of rodents. Although we found the expected negative relationship between call frequency and body mass, we found no significant differences in acoustic characteristics between closed and open‐habitat species. The results of the present study show that the acoustic frequencies of alarm calls can provide reliable information about the size of a sender in this taxonomic group, although they generally do not support the acoustic adaptation hypothesis.     

Brains and bravery: Little evidence of a relationship between brain size and flightiness in shorebirds

The ability of birds to perceive, assess and appropriately respond to the presence of relatively novel threats is important to their survival. We hypothesized that the cognitive capacity of birds will influence their ability for accurate response to novelty. We used brain volume as a surrogate for cognitive capacity and postulated that larger brained birds would moderate their responses when presented with a benign, frequently occurring stimulus, such as a person, because they would habituate more readily. We conducted phylogenetic generalized least square regression to investigate the relationship between brain volume and flight initiation distance (FID; the distance to which a bird can be approached before initiating escape behaviour), while controlling for confounding factors including body size (body mass and wing length) and migration status. We compared seven different models using combinations of these parameters using Akaike's information criterion to determine the best approximating model(s) explaining FID. The two best‐supported models included only wing length and only body mass with Akaike weights of 0.396 and 0.311 respectively. No model including brain volume had an Akaike weight greater than 0.083 and brain volume was poorly correlated with FID in models after controlling for body mass. Thus, brain volume does not appear to strongly relate to bravery among these shorebirds.