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1. Late Holocene spread of pastoralism coincides with endemic megafaunal extinction on Madagascar

   https://doi.org/https://doi.org/10.1098/rspb.2021.1204  

   Hixon, S.; Douglass, K.; Crowley, B.; Rakotozafy, L.; Clark, G.; Anderson, A.; Haberle, S.; Ranaivoarisoa, J.; Buckley, M.; Fidiarisoa, S.; et al (July 2021, Proceedings of the Royal Society of London)

   Recently expanded estimates for when humans arrived on Madagascar (up to approximately 10 000 years ago) highlight questions about the causes of the island's relatively late megafaunal extinctions (approximately 2000–500 years ago). Introduced domesticated animals could have contributed to extinctions, but the arrival times and past diets of exotic animals are poorly known. To conduct the first explicit test of the potential for competition between introduced livestock and extinct endemic megafauna in southern and western Madagascar, we generated new radiocarbon and stable carbon and nitrogen isotope data from the bone collagen of introduced ungulates (zebu cattle, ovicaprids and bushpigs, n = 66) and endemic megafauna (pygmy hippopotamuses, giant tortoises and elephant birds, n = 68), and combined these data with existing data from endemic megafauna (n = 282, including giant lemurs). Radiocarbon dates confirm that introduced and endemic herbivores briefly overlapped chronologically in this region between 1000 and 800 calibrated years before present (cal BP). Moreover, stable isotope data suggest that goats, tortoises and hippos had broadly similar diets or exploited similar habitats. These data support the potential for both direct and indirect forms of competition between introduced and endemic herbivores. We argue that competition with introduced herbivores, mediated by opportunistic hunting by humans and exacerbated by environmental change, contributed to the late extinction of endemic megafauna on Madagascar. 

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2. Birds can transition between stable and unstable states via wing morphing

   https://doi.org/10.1038/s41586-022-04477-8  

   Harvey, C.; Baliga, V. B.; Wong, J. C.; Altshuler, D. L.; Inman, D. J. (March 2022, Nature)

   Abstract Birds morph their wing shape to accomplish extraordinary manoeuvres 1–4 , which are governed by avian-specific equations of motion. Solving these equations requires information about a bird’s aerodynamic and inertial characteristics 5 . Avian flight research to date has focused on resolving aerodynamic features, whereas inertial properties including centre of gravity and moment of inertia are seldom addressed. Here we use an analytical method to determine the inertial characteristics of 22 species across the full range of elbow and wrist flexion and extension. We find that wing morphing allows birds to substantially change their roll and yaw inertia but has a minimal effect on the position of the centre of gravity. With the addition of inertial characteristics, we derived a novel metric of pitch agility and estimated the static pitch stability, revealing that the agility and static margin ranges are reduced as body mass increases. These results provide quantitative evidence that evolution selects for both stable and unstable flight, in contrast to the prevailing narrative that birds are evolving away from stability 6 . This comprehensive analysis of avian inertial characteristics provides the key features required to establish a theoretical model of avian manoeuvrability. 

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3. The impacts of body mass on immune cell concentrations in birds

   https://doi.org/10.1098/rspb.2020.0655  

   Ruhs, Emily Cornelius; Martin, Lynn B.; Downs, Cynthia J. (September 2020, Proceedings of the Royal Society B: Biological Sciences)

   null (Ed.)

   Body mass affects many biological traits, but its impacts on immune defences are fairly unknown. Recent research on mammals found that neutrophil concentrations disproportionately increased (scaled hypermetrically) with body mass, a result not predicted by any existing theory. Although the scaling relationship for mammals might predict how leucocyte concentrations scale with body mass in other vertebrates, vertebrate classes are distinct in many ways that might affect their current and historic interactions with parasites and hence the evolution of their immune systems. Subsequently, here, we asked which existing scaling hypothesis best-predicts relationships between body mass and lymphocyte, eosinophil and heterophil concentrations—the avian functional equivalent of neutrophils—among more than 100 species of birds. We then examined the predictive power of body mass relative to life-history variation, as extensive literature indicates that the timing of key life events has influenced immune system variation among species. Finally, we ask whether avian scaling patterns differ from the patterns we observed in mammals. We found that an intercept-only model best explained lymphocyte and eosinophil concentrations among birds, indicating that the concentrations of these cell types were both independent of body mass. For heterophils, however, body mass explained 31% of the variation in concentrations among species, much more than life-history variation (4%). As with mammalian neutrophils, avian heterophils scaled hypermetrically ( b = 0.19 ± 0.05), but more steeply than mammals (approx. 1.5 ×; 0.11 ± 0.03). As such, we discuss why birds might require more broadly protective cells compared to mammals of the same body size. Overall, body mass appears to have strong influences on the architecture of immune systems. 

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4. Geomagnetic disturbance associated with increased vagrancy in migratory landbirds

   https://doi.org/10.1038/s41598-022-26586-0  

   Tonelli, Benjamin A.; Youngflesh, Casey; Tingley, Morgan W. (January 2023, Scientific Reports)

   Abstract Rare birds known as “accidentals” or “vagrants” have long captivated birdwatchers and puzzled biologists, but the drivers of these rare occurrences remain elusive. Errors in orientation or navigation are considered one potential driver: migratory birds use the Earth’s magnetic field—sensed using specialized magnetoreceptor structures—to traverse long distances over often unfamiliar terrain. Disruption to these magnetoreceptors or to the magnetic field itself could potentially cause errors leading to vagrancy. Using data from 2 million captures of 152 landbird species in North America over 60 years, we demonstrate a strong association between disruption to the Earth’s magnetic field and avian vagrancy during fall migration. Furthermore, we find that increased solar activity—a disruptor of the avian magnetoreceptor—generally counteracts this effect, potentially mitigating misorientation by disabling the ability for birds to use the magnetic field to orient. Our results link a hypothesized cause of misorientation to the phenomenon of avian vagrancy, further demonstrating the importance of magnetoreception among the orientation mechanisms of migratory birds. Geomagnetic disturbance may have important downstream ecological consequences, as vagrants may experience increased mortality rates or facilitate range expansions of avian populations and the organisms they disperse. 

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5. Leukocyte allometries in birds are not affected by captivity

   https://doi.org/10.1002/jez.2591  

   Martin, Lynn B.; Ruhs, Emily Cornelius; Oakey, Samantha; Downs, Cynthia J. (March 2022, Journal of Experimental Zoology Part A: Ecological and Integrative Physiology)

   Abstract Body size affects many traits, but often in allometric, or disproportionate ways. For example, large avian and mammalian species circulate far more of some immune cells than expected for their size based on simple geometric principles. To date, such hypermetric immune scaling has mostly been described in zoo‐dwelling individuals, so it remains obscure whether immune hyper‐allometries have any natural relevance. Here, we asked whether granulocyte and lymphocyte allometries in wild birds differ from those described in captive species. Our previous allometric studies of avian immune cell concentrations were performed on animals kept for their lifetimes in captivity where conditions are benign and fairly consistent. In natural conditions, infection, stress, nutrition, climate, and myriad other forces could alter immune traits and hence mask any interspecific scaling relationships between immune cells and body size. Counter to this expectation, we found no evidence that immune cell allometries differed between captive and wild species, although we had to rely on cell proportion data, as insufficient concentration data were available for wild species. Our results indicate that even in variable and challenging natural contexts, immune allometries endure and might affect disease ecology and evolution. 

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