Body Mass Of Birds Research Articles

A country‐wide examination of effects of urbanization on common birds

AbstractUrbanization forms one of the most drastic alterations of the environment and poses a major threat to wildlife. The human–induced modifications of the landscape may affect individual's fitness resulting in population declines. Research on how urbanization affects fitness traits has shown mixed results. However, studies typically contrasted data from a single species from few urban and non‐urban sites collected over short timeframes. Examining multiple species across a broad urbanization gradient enables a more robust comparison and understanding of how different species are impacted by urbanization‐knowledge crucial for generating population predictions, which are essential for conservation management. Here, we use data from a nation‐wide citizen science project to examine variation in survival and relative body mass and size (wing length) of common passerine birds, collected along an urbanization gradient in the Netherlands over an 8‐year period. Urbanization was measured as the distance from the city's border and the proportion of impervious surface area. Although the overall association between urbanization and survival was slightly negative, there was support for lower survival closer to the city in three species (chiffchaff Phylloscopus collybita, European robin Erithacus rubecula, European greenfinch Chloris chloris) and higher survival closer to the city in two (great tit Parus major and house sparrow Passer domesticus) of the 11 species examined. The contrasting survival successes among species suggest that ongoing urbanization may lead to shifts in community structure and loss of biodiversity. Impacts of urbanization on relative mass and size also exhibited varying effects, albeit less pronounced, and these effects were not correlated with the effects on survival. This implies that body mass and size cannot be used as indicators for urban‐associated patterns of survival. Our results further imply that effective conservation management targeting bird communities should involve a range of diverse actions, as focusing on single measures is unlikely to simultaneously impact multiple species due to the variation in responses to urbanization.

Afromontane understory birds increase in body size over four decades

Of the myriad responses to climate change, an emerging trend is the widespread decrease in animal body size with warming temperatures. Birds, in particular, have been shown to be decreasing in body size in several areas – most notably the Amazon Basin and temperate North America – but trends in much of the world remain unexplored. Here, we analyze temporal trends and climatic associations of body mass for 42 resident bird species over 36 years in the Usambara Mountains of Tanzania, a tropical montane global biodiversity hotspot. In addition, we assess trends in wing length and mass:wing ratio over 21 years. Finally, we examine whether species‐specific trends in body mass are related to average body size or to trends in apparent survival. Overall, species' average body mass in the Usambara Mountains increased by 0.023 g decade‐1, amounting to increases of 4.1% over 36 years. These long‐term shifts in body mass were strongly and positively associated with annual mean temperature but showed no relationship with precipitation. Wing length increased on average by 2.0% over a 21‐year period, yet there was mixed evidence for trends in mass:wing ratio, suggesting that body size in general is increasing. While percentage trends in body mass were not related to trends in apparent annual survival, smaller species did display greater proportional increases in body mass. Although the drivers of increased body size remain unclear – and climate change cannot be ruled out – such increases among Afrotropical montane birds provide an intriguing counterpoint to observed declines in body mass elsewhere and suggest that trends in body mass in tropical birds may be mediated by biogeography or other abiotic or biotic drivers.

Relationship between Fat Status, Stage of Gonadal Maturity and Hormonal Variation of Turdus philomelos (C.L. Brehm, 1831) Wintering in Apulia during 2018-2020.

In this study, we aimed to evaluate the development of the fattening condition and the reproductive status of the song thrush from December to February. For this purpose, the chemical and fatty acid compositions of the pectoral muscle were analyzed in relation to the fattening state of the birds. Moreover, their reproductive activity was evaluated via the anatomical and pathological examination of tissues and through the assessment of sex steroid profiles. One hundred ninety-five thrushes captured by local hunters during the 2018-2019 and 2019-2020 hunting seasons in different provinces of the Apulia region in Italy were used. The first step was the measurement of bird body mass, and the amount of subcutaneous body fat was estimated visually. During post-mortem examinations, the pectoral muscle was excised and used for chemical and fatty acid analysis and a hormone assay, respectively. Moreover, ovaries and testicles were evaluated to determine the degree of maturation and thus the reproductive status of the birds. The results regarding fattening status and fatty acid profile confirmed that in January-February, thrushes change their diet, increasing their intake of oleic acid, likely to better cope with low temperatures and prepare for long-distance migration. In both male and female thrushes, the concentrations of sex hormones confirmed a phase of reproductive quiescence from December to February, which was also confirmed through histological examination of the gonads.

House sparrows are heavier on organic and integrated-production farms than on conventional farms

The negative impact of conventional farming on avian biodiversity has been increasingly documented. However, the potential effects of different farming practices on bird populations' health remain unclear. We aimed to investigate whether different farming practices (organic, integrated production, conventional/intensive) have differential effects on the body mass - as a proxy for body condition - and biomarkers of oxidative stress in house sparrows (Passer domesticus), a model species strongly associated with human activities and still abundant in Switzerland. We captured a total of 681 birds in 19 organic farms, 20 integrated-production farms (labelled “IP-Suisse”) and 18 conventional farms, and measured bird body mass and tarsus length, as well as levels of malondialdehydes (MDA, a marker of oxidative damage to lipids), superoxide dismutase (SOD, a first-line antioxidant enzyme) activity, and the ratio of oxidized over reduced glutathione (GSSG/GSH, a marker of cellular oxidative stress) in blood and sperm as biomarkers of the systemic oxidative stress endured by birds. Our findings show that house sparrows living in integrated and organic farms were 2.39 % and 4.33 % heavier than birds living in conventional farms, but we did not find any difference in tarsus length, suggesting that birds were of similar size. In addition, we did not find any difference in oxidative stress markers across farming practices. Our results highlight the potential benefits of sustainable farming practices, such as organic and integrated farming, for bird populations and emphasize the need for mitigating the negative impact of agricultural intensification on biodiversity through practices that may enhance the birds’ health and thus lead to positive population dynamics.

Selective logging intensity and time since logging drive tropical bird and dung beetle diversity: a case study from Amazonia

SummaryUnderstanding how selective logging affects biodiversity is crucial to planning cost-effective conservation strategies in tropical forests, yet there is limited understanding of its impacts on fauna functional diversity in the tropical Americas. We assessed how selective logging intensification and time since logging influence multiple metrics of fauna functional integrity in the Brazilian Amazon by collecting bird and dung beetle data within 48 logging management units that had experienced varying exploitation intensities between 1.5–2.0 and 5.0–6.0 years before the faunal surveys. We investigated assemblage responses and used functional attributes to assess changes in functional diversity, specialization, originality and species rarity. Using point counts and pitfall traps, we collected 5081 records of 182 bird species and 7892 dung beetles from 45 species. Logging intensification led to significant declines in most dung beetle responses and bird body mass, whereas time since logging was a key driver of dung beetle and bird functional and taxonomic diversity. Our study presents novel empirical evidence of how logging intensification effects vary across taxa, ecological metrics and time since logging, which is key to informing forest conservation and further investigating environmental degradation impacts on tropical biodiversity.

Photoperiodic response of a subtropical Passerine, the red-vented bulbul, Pycnonotus cafer stanfordi Deignan

: In the present study, photoperiodic response of red-vented bulbuls, Pycnonotus cafer stanfordi Deignan was studied at Lumami (26oN), Zunheboti district, Nagaland. In birds kept under natural lighting, testicular and follicular developments began in February (daylength 11.5 hr/day); gonads developed progressively through March-May period (12-13 hrs/day), peaked in June (13hr, 34min/day) and thereafter declined to reach smaller in size during September. Seasonal changes in the size and activity of gonads were abolished in birds transferred to fixed duration of 10L/14D during December (quiescent phase). Under constant 16L/8D and 20L/4D photoperiods, gonads developed almost at similar pace, peaked in 3 months of exposure and thereafter, regressed fully during next 3 months owing probably to the development of photorefractoriness. Absolute development of gonads was not significantly different in groups kept under natural lighting (13hr, 34min/day), 16L/ 8D and 20L/4D daylengths. Body mass cycles of birds kept under NDL, 16L/8D and 20L/4D were temporally similar to gonadal cycles. No significant change occurred in the body mass of birds exposed to constant 10L/14D. It may be suggested that some common mechanisms engender photoinduced changes in gonad and body mass of red-vented bulbuls and daylengths higher than what birds experience naturally are superfluous in impacting the neuroendocrine and metabolic mechanisms.

Individual body mass and sex of a frugivorous bird affect the quality of seed dispersal

AbstractFrugivorous animals play crucial roles dispersing seeds away from parental plants and influencing plant recruitment. Most studies focus on comparisons of seed dispersal services provided by distinct species of animals, but neglect how within‐species variation may affect dispersal. Individual traits, such as body mass and sex, are related to metabolic rates, gut load capacity, and transit times that potentially influence dispersal quantity and quality. Here, we aim at answering if individual traits (body mass and sex) of Pale‐breasted Thrushes (Turdus leucomelas) affect seed dispersal quality by testing the following hypotheses (a) individual traits influence seed retention time and germination, (b) seed retention time affects seed germination, and (c) seed passage through the gut enhances germination. We found that females retained seeds in the gut for longer periods than males. Gut passed and manually depulped seeds had similar germination success. However, heavier birds, irrespective of sex, had longer seed retention times and promoted higher germination. Our results indicate that intraspecific differences in morphological traits of frugivores are a source of variation in dispersal outputs and may help to explain complex patterns of seed dispersal. We highlight the importance of considering the quality of seed dispersal at an individual‐level, as well as at a species‐level, and reinforce that some individuals may contribute more to seed germination, and potentially recruitment, than others. Finally, a decrease in body masses of tropical birds in response to global warming may cascade to a decrease in seed dispersal quality.Abstract in Portuguese is available with online material.

How many seeds can birds disperse?: Determining the pattern of seed deposition by frugivorous birds

Frugivorous birds are the primary seed dispersers for fleshy-fruited plants through defecation. In general, small-sized species disperse seeds across short distances from parental plants. However, multiple seeds or seeds of different plant species are frequently mixed in the fecal mass, because birds are prone to eat multiple fruits of a few plant species during foraging. This suggests birds deposit seeds as clumps in the field, causing inter- and intraspecific competition. However, the exact number of dispersed seeds for each defecation is very hard to estimate in field. It may also vary according to several variables, such as body size of birds and number of seeds per fruit. To clarify seed deposition patterns, we captured small frugivorous birds and collected the feces and regurgitations. The number of seeds excreted in fecal samples was investigated. From 2003 to 2019, a total number of 21518 seeds from 60 plant species were collected from 2214 birds of 17 species. Average number of seeds included in the fecal sample was 9.7 ± SD 18.4 (range: 1–340). The frequency of the number of excreted seeds was not normally distributed and the mode value was one in all cases and for five main dispersers. In most cases (64.8–74.5%), birds excreted a single seed. Furthermore, the effects of morphological traits of birds and plants on number of excreted seeds were analyzed using GLMM. The body mass of birds had a positive effect on the number of excreted seeds. However, fruit and seed weight exhibited negative effects, suggesting the number of excreted seeds is smaller when smaller birds eat larger fruits bearing larger seeds. The seed deposition pattern based on excretion of a single seed may avoid seed and seedling aggregation at local sites.

Coracoid strength as an indicator of wing-beat propulsion in birds.

Birds generate a propulsive force by flapping their wings. They use this propulsive force for various locomotion styles, such as aerodynamic flight, wing-paddle swimming and wing-assisted incline running. It is therefore important to reveal the origin of flapping ability in the evolution from theropod dinosaurs to birds. However, there are no quantitative indices to reconstruct the flapping abilities of extinct forms based on their skeletal morphology. This study compares the section modulus of the coracoid relative to body mass among various extant birds to test whether the index is correlated with flapping ability. According to a survey of 220 historical bird specimens representing 209 species, 180 genera, 83 families and 30 orders, the section modulus of the coracoid relative to body mass in non-flapping birds was significantly smaller than that of flapping birds. This indicates that coracoid strength in non-flapping birds is deemphasised, whereas in flapping birds the strength is emphasisedto withstand the contractile force produced by powerful flapping muscles, such as the m. pectoralis and m. supracoracoideus. Therefore, the section modulus of the coracoid is expected to be a powerful tool to reveal the origin of powered flight in birds.

Human perception relates to when endangered species are listed

The species endangerment listing process is governed not solely by causal factors but also by human perception, particularly as it relates to observability. Because human perception is important in species detection, we hypothesized that ecological indicators associated with human perception would change noticeably over time. Testing our hypothesis on species listed under the US Endangered Species Act, we found that – in general and across (not within) different taxa – body mass and geographic range of listed species decreased over time and that animals that produced vocalizations and exhibited grouping behavior were listed earlier than silent and solitary animals. Specifically, since the year of their listing, the body mass of birds, mammals, and reptiles decreased, whereas the body mass of amphibians increased; likewise, the geographic range of insects, mammals, and plants contracted, whereas the geographic range of amphibians, bivalves, birds, and fish slightly expanded. Our results demonstrate a temporal shift in endangered species listings, suggesting that approaches to listing species may need to be reevaluated and methodologically revised.

Orthologous microsatellites, transposable elements, and DNA deletions correlate with generation time and body mass in neoavian birds.

The rate of mutation accumulation in germline cells can be affected by cell replication and/or DNA damage, which are further related to life history traits such as generation time and body mass. Leveraging the existing datasets of 233 neoavian bird species, here, we investigated whether generation time and body mass contribute to the interspecific variation of orthologous microsatellite length, transposable element (TE) length, and deletion length and how these genomic attributes affect genome sizes. In nonpasserines, we found that generation time is correlated to both orthologous microsatellite length and TE length, and body mass is negatively correlated to DNA deletions. These patterns are less pronounced in passerines. In all species, we found that DNA deletions relate to genome size similarly as TE length, suggesting a role of body mass dynamics in genome evolution. Our results indicate that generation time and body mass shape the evolution of genomic attributes in neoavian birds.

Congeneric predators fill discrete niches created by the relative abundances of their prey species

To what degree is niche partitioning driven by underlying patterns in resources such as food, rather than by competition itself? Do discrete niches exist? We address these questions in the context of Cooper's and sharp‐shinned hawks, two broadly sympatric, North American, bird‐eating raptors in the genus Accipiter. We find that the resource base, as quantified by body masses of birds at bird feeders, is approximately lognormal (smallest birds are most abundant), with lesser modes (peaks) in abundance at larger body mass. The predators appear to exploit peaks in the resource base, with sharp‐shinned hawks focusing on small prey items (median of 26.5 g), and Cooper's hawks taking prey from the two most abundant peaks (both the small body mass peak and a lesser peak at medium body mass ~90 g). We tested the ability of citizen scientists to distinguish these notoriously similar species, and we determined the influence of potential false positive detections on our conclusions. We find that citizen scientists struggle to distinguish these predators from one another, and 18% of Cooper's hawks were identified as sharp‐shinned hawks, while 27% of sharp‐shinned hawks were identified as Cooper's hawks. Yet, simulations show that this uncertainty did not jeopardize our qualitative conclusions.

Plasma lactate dehydrogenase and pyruvate kinase activity changes with body mass and age across birds and mammals

Abstract Birds and mammals produce most adenosine triphosphate (ATP) through mitochondrial oxidative phosphorylation, but when oxygen is not present in sufficient levels, ATP can be produced through anaerobic glycolysis. Pyruvate kinase (PK) catalyzes the final step of glycolysis by converting phosphoenolpyruvate and adenosine diphosphate (ADP) into pyruvate and ATP. Lactate dehydrogenase (LDH) is important for anaerobic glycolysis by catalyzing the conversion of pyruvate into lactate. In this study, we measured LDH and PK activities in plasma from birds and mammals in order to determine the relationship between LDH and PK with respect to body mass and age. Our results show that birds had a higher LDH and PK activity compared with mammals. There is a positive relationship between body mass and plasma LDH activity in birds only. However, this relationship disappears when the data are phylogenetically corrected. We did not observe a significant relationship between plasma LDH and age in birds or mammals. Plasma PK activity was negatively correlated with body mass in birds but not in mammals and positively associated with age in both birds and mammals. The relationship between LDH and PK with respect to body mass and age may be complex due to differences in metabolism in birds and mammals. Increases in LDH and PK activity with body mass in birds may be linked to anaerobic demands of flight, especially in larger birds. A decrease in LDH activity with age/MLSP (maximum lifespan) in mammals may reflect a differing metabolic shift as compared with birds. Increases in PK with age in both mammals and birds may help them cope with greater energetic needs as cells age.

Cecal Microbial Hydrogen Cycling Potential Is Linked to Feed Efficiency Phenotypes in Chickens.

In chickens, early life exposure to environmental microbes has long-lasting impacts on gastrointestinal (GI) microbiome development and host health and growth, via mechanisms that remain uncharacterized. In this study, we demonstrated that administrating a fecal microbiome transplant (FMT) from adults to day-of-hatch chicks results in significantly higher body mass of birds and decreased residual feed intake (RFI), implying enhanced feed efficiency, at 6 weeks of age. To assess the potential mechanisms through which FMT affects adult bird phenotype, we combined 16 S rRNA gene amplification, metagenomic, and comparative genomic approaches to survey the composition and predicted activities of the resident microbiome of various GI tract segments. Early life FMT exposure had a long-lasting significant effect on the microbial community composition and function of the ceca but not on other GI segments. Within the ceca of 6-week-old FMT birds, hydrogenotrophic microbial lineages and genes were most differentially enriched. The results suggest that thermodynamic regulation in the cecum, in this case via hydrogenotrophic methanogenic and sulfur-cycling lineages, potentially serving as hydrogen sinks, may enhance fermentative efficiency and dietary energy harvest capacity. Our study provides a specific mechanism of action through which early-life microbiome transplants modulate market-relevant phenotypes in poultry and, thereby, may represent a significant advance toward microbiome-focused sustainable agriculture.

Effects of forest fragmentation on the weight of understory birds at the Biological Dynamics of Forest Fragments Project in Amazonia

AbstractDeforestation and habitat fragmentation are known as the chief drivers of biodiversity loss. Less is known about the condition of species and individuals that remain in disturbed habitats. Theory predicts that resources are more limited after compared with before fragment isolation. Thus, we assessed how body condition of individual birds' changes in response to forest fragment isolation. We compared weights of the same individually banded birds caught in mist nets within 5 years before and after fragment isolation and assessed the population‐level changes of three species at the Biological Dynamics of Forest Fragments Project in the Brazilian Amazon. We predicted that fragment isolation would result in reduced weight for all bird species. Out of the 3466 bird mist net captures before and after isolation in the 1980s and the 2150 birds captured before and after re‐isolation of fragments in the 2010s, only 73 adult individuals from 36 different species were recaptured, suggesting that few individuals stay in fragments. Contrary to predictions, insectivorous species that remained in fragments gained weight (3.43%) after fragment isolation while frugivorous birds maintained a stable weight. While recent studies report long‐term declines in body mass of birds in tropical unfragmented tropical forests, our results provide a novel analysis into how avian body mass responds to habitat fragmentation. Further studies on the body condition of individuals that remain in fragments and the ultimate consequences of fluctuations in body condition are needed to better understand why some individuals and species are more susceptible to forest fragmentation than others.Abstract in Portuguese is available with online material

Predicting consistent foraging ecologies of migrating waterbirds: Using stable isotope and parasite measurements as indicators of landscape use

The emergence of novel human pathogens is frequently linked with zoonotic events and human-wildlife interactions that promote disease transmission. Consequently, surveillance of wildlife populations for candidate diseases that could spread to humans is beneficial, but requires widespread collections of numerous samples. A legitimate means to acquire large sample sizes of waterfowl is through cooperation between researchers and hunters, who also work in concert with natural resource managers, landowners, and agricultural entities -e.g., aquaculture facilities. In addition to understanding the occurrence and spread of parasites and pathogens by birds, these samples can be used to answer questions about the ecology of various waterbird species. Body mass and morphometric data on hunter-donated specimen are useful for understanding bird condition and other dynamics of birds; however, when breast meat is removed prior to the acquisition of specimen weight, samples might not be as desirable. Here, we evaluate the utility of data obtained from a bird species that might be targeted by hunters and subsequently used to learn about their disease dynamics. Lesser Scaup (Aythya affinis) collected at aquaculture facilities were assessed for their stable isotope concentrations and parasites communities to learn about the birds’ foraging ecology. Discriminant analyses designed to classify birds by the aquaculture pond type from which they were collected included isotope data, Principal Components derived from parasite community data of 7 types, and birds’ body mass. We compared these to Double-crested Cormorants (Nannopterum auritum) feeding on catfish and found the two waterbird species exhibited different infracommunities of parasites Furthermore, some scaup demonstrated fish aquaculture pond type fidelity. Bird body mass was an important metric to include in analytical models when all parasite datatypes were not available. However, the combination of stable isotope concentrations and parasite infracommunity data (that includes prevalence, abundance, volume, and energy use) in models resulted in host ecology differentiation equal or better than models where bird body mass was included. Hunter-derived samples should be encouraged as a means for sample acquisition and be considered as an approach for aquaculture-wildlife conflict management as the information that can be obtained through these samples is multifaceted.

Variation in bird taxonomic distinctness, but not body mass or niche overlap, explains the robustness of Neotropical seed dispersal networks

Abstract Frugivory and seed dispersal are fundamental ecological processes for the maintenance and conservation of tropical forest areas and ecosystem resilience. Here we investigated factors that could affect the relationship between frugivorous birds and fruit consumption, such as body mass, niche relationships, and species taxonomic groups, and the effects of such factors on the robustness of mutualistic bird-plant interaction networks. More specifically, we used Horn-Morisita niche overlap, the body mass coefficient of variation, and the variation in taxonomic distinctness index (varTD) as explanatory variables, and we applied multiple linear regression to test the that increased robustness in bird-plant frugivory networks occurs where birds have larger trophic niche overlaps and lower body mass variations and decreased robustness where they are more taxonomically diverse, in response to less functional redundancy. The analysis was based on literature data and fecal samples of birds collected after mist netting procedures. Bird body mass and niche overlap did not explain the variation in robustness in seed dispersal networks. However, different from expected, the results showed an effect of variations in taxonomic distinctness, suggesting that the larger the taxonomic distinctness of birds in a frugivore assemblage, the larger the robustness of the networks. Some hypotheses were suggested to explain this effect. Regardless of the factors that lead varTD to favor the robustness of mutualistic bird-plant networks, the results demonstrated that conserving diversity above the species level, and not just species limited to a few taxonomic groups, can be an important strategy for ecosystem conservation over time.

Diet of Mesozoic toothed birds (Longipterygidae) inferred from quantitative analysis of extant avian diet proxies

BackgroundBirds are key indicator species in extant ecosystems, and thus we would expect extinct birds to provide insights into the nature of ancient ecosystems. However, many aspects of extinct bird ecology, particularly their diet, remain obscure. One group of particular interest is the bizarre toothed and long-snouted longipterygid birds. Longipterygidae is the most well-understood family of enantiornithine birds, the dominant birds of the Cretaceous period. However, as with most Mesozoic birds, their diet remains entirely speculative.ResultsTo improve our understanding of longipterygids, we investigated four proxies in extant birds to determine diagnostic traits for birds with a given diet: body mass, claw morphometrics, jaw mechanical advantage, and jaw strength via finite element analysis. Body mass of birds tended to correspond to the size of their main food source, with both carnivores and herbivores splitting into two subsets by mass: invertivores or vertivores for carnivores, and granivores + nectarivores or folivores + frugivores for herbivores. Using claw morphometrics, we successfully distinguished ground birds, non-raptorial perching birds, and raptorial birds from one another. We were unable to replicate past results isolating subtypes of raptorial behaviour. Mechanical advantage was able to distinguish herbivorous diets with particularly high values of functional indices, and so is useful for identifying these specific diets in fossil taxa, but overall did a poor job of reflecting diet. Finite element analysis effectively separated birds with hard and/or tough diets from those eating foods which are neither, though could not distinguish hard and tough diets from one another. We reconstructed each of these proxies in longipterygids as well, and after synthesising the four lines of evidence, we find all members of the family but Shengjingornis (whose diet remains inconclusive) most likely to be invertivores or generalist feeders, with raptorial behaviour likely in Longipteryx and Rapaxavis.ConclusionsThis study provides a 20% increase in quantitatively supported fossil bird diets, triples the number of diets reconstructed in enantiornithine species, and serves as an important first step in quantitatively investigating the origins of the trophic diversity of living birds. These findings are consistent with past hypotheses that Mesozoic birds occupied low trophic levels.

Are there changes in morphometrics of migratory juvenile Rough-legged Hawks (Buteo lagopus) in north-central North America?

Global rising temperatures due to recent climate change have been linked to long-term reductions in body mass and wing chord in migratory birds, including raptors. The Arctic is experiencing higher temperatures compared to the global mean and such high-latitude increases could influence the morphometrics of the tundra-breeding Rough-legged Hawk (Buteo lagopus). Linear regression models showed no statistically significant changes in body mass or wing chords in migratory juvenile male and female Rough-legged Hawks captured and banded across 48 years at Duluth, Minnesota, 1973–2020. Captures of Rough-legged Hawks at our migration stations provided a relatively expedient means by which to monitor possible climate-induced long-term changes in morphometrics of an Arctic species that is difficult to sample in inaccessible tundra settings.

Inter‐relationships among body mass, jaw musculature and bite force in birds

AbstractBite force can provide an insight into the feeding biomechanics and ecology of vertebrates. There has been an increasing interest in bite force in birds with data being collected using force transducers although bite forces have also been calculated from the mass of the jaw musculature. Studies have sought to find ecological correlates between bite force and diet or feeding style as well as with morphology. This study collated data reported in the literature for bite force and mass of the jaw musculature in birds and explored the relationships between these variables and their relationships with body mass to test two hypotheses. First, bite force and mass of the jaw musculature would scale with body mass irrespective of the phylogeny. Second, bite force and mass of the jaw musculature would be directly related to each other and be unrelated to phylogeny. Phylogenetically controlled analyses showed that in relation to body mass there were different relationships with bite force, and with the mass of the jaw musculature, for non‐passerine (isometry and negative allometry, respectively) and passerine species (both positive allometry). By contrast, a single significantly positively allometric relationship described the relationship between jaw muscle mass and bite force. These relationships were driven in part by the diet of the species concerned but also may reflect morphological differences in jaw musculature. The few studies that compare measured and calculated bite force for the same species show that values derived from muscles were higher. Detaching muscles from their points of origin and insertion to calculate physiological cross‐sectional area may be biasing bite force calculations.