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opencc-zeroApr 2020View details →

Data from: Mechanical and structural adaptations to migration in the flight feathers of a Palaearctic passerine

Current avian migration patterns in temperate regions have been developed during the glacial retreat and subsequent colonization of the ice-free areas during the Holocene. This process resulted in a geographic gradient of greater seasonality as latitude increased that favoured migration-related morphological and physiological (co)adaptations. Most evidence of avian morphological adaptations to migration comes from the analysis of variation in the length and shape of the wings, but the existence of intra-feather structural adjustments has been greatly overlooked despite their potential to be under natural selection. To shed some light on this question, we used data from European robins Erithacus rubecula overwintering in Campo de Gibraltar (Southern Iberia), where sedentary robins coexist during winter with conspecifics showing a broad range of breeding origins and, hence, migration distances. We explicitly explored how wing length and shape, as well as several functional (bending stiffness), developmental (feather growth rate) and structural (size and complexity of feather components) characteristics of flight feathers varied in relation to migration distance, which was estimated from the hydrogen stable isotope ratios of the summer-produced tail feathers. Our results revealed that migration distance not only favoured longer and more concave wings, but also promoted primaries with a thicker dorsoventral rachis and shorter barb lengths, which in turn conferred more bending stiffness to these feathers. We suggest that these intra-feather structural adjustments could be an additional, largely unnoticed, adaptation within the avian migratory syndrome that might have the potential to evolve relatively quickly to facilitate the occupation of seasonal environments.

opencc-zeroApr 2024View details →

The respiratory system influences flight mechanics in soaring birds

The subpectoral diverticulum (SPD) is an extension of the respiratory system in birds that dives between the primary muscles responsible for flapping the wing. Surveying the pulmonary apparatus in 68 species showed that the SPD was present in virtually all soaring taxa investigated yet absent in non-soarers. We find that this structure independently evolved with soaring flight at least seven times, indicating that the diverticulum may have a functional and adaptive relationship with this flight style. Using the soaring hawks Buteo jamaicensis and B. swainsoni as models, we show that the SPD is not integral for ventilation, that an inflated SPD can increase the moment arm of cranial parts of the pectoralis, and that pectoralis muscle fascicles are significantly shorter in soaring hawks than in non-soaring birds. This coupling of an SPD-mediated increase in pectoralis leverage with force-specialised muscle architecture produces a pneumatic system adapted for the isometric contractile conditions expected in soaring flight. The discovery of a mechanical role for the respiratory system in avian locomotion underscores the functional complexity and heterogeneity of this organ system and suggests that pulmonary diverticula likely have other undiscovered secondary functions. These data provide a mechanistic explanation for the repeated appearance of the SPD in soaring lineages, demonstrating that the respiratory system can be co-opted to provide novel biomechanical solutions to the challenges of flight and thereby influence the evolution of avian volancy.

publicApr 2024View details →

The respiratory system influences flight mechanics in soaring birds

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publicApr 2020View details →

Data from: Mechanical and structural adaptations to migration in the flight feathers of a Palaearctic passerine

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Figure 4 in Mechanisms preventing animals to achieve buoyant flight

Figure 4. Oeda's wing surface as a function of thorax volume. Points represent specimens and lines represent the best fit of a generalised linear mixed model using species as random effects. Thorax volume and forewing area are presented as ratios to body mass, to control for body size.

Figure 3 in Mechanisms preventing animals to achieve buoyant flight

Figure 3. Oeda species' (A) thorax volume relative to body mass; (B) buoyancy capability in their environment with the sun heating air inside the thorax; and (C) thorax volume necessary for buoyancy to overcome body weight.

Figure 2 in Mechanisms preventing animals to achieve buoyant flight

Figure 2. Animal buoyancy across theoretical conditions of body cavity size and density differential relative to the environment. Coloured symbols and lines represent median values of Oeda species with thoraxes filled with sun-heated air. Dotted lines depict density differentials with cavities filled with air, methane, and hydrogen at a presumed physiological thermal limit of 15°C above the environment (Hoffman et al. 2013). The y-axis points at which dotted lines intersect with the limit of the black area represent the buoyant cavity volumes necessary to overcome the body weight. Calculations based on reference conditions of environment temperature of 15°C and air density of 1.225 kg/m3.

Figure 1 in Mechanisms preventing animals to achieve buoyant flight

Figure 1. Oeda species and their distribution over the Amazon. Note the overall high air density across the species distribution.

opencc-zeroDec 2018View details →

Data from: Sexual size dimorphism, prey morphology, and catch success in relation to flight mechanics in the Peregrine Falcon: a simulation study

In common with many other raptors, female Peregrine Falcons Falco peregrinus are about 50% heavier than males. Their sexual dimorphism is thought to allow breeding pairs to exploit a wider range of prey through a division of labor: the male being able to catch more maneuverable prey species; the female capable of carrying larger ones. Given the difficulty of assessing the catch success and load carrying capacity of both sexes of falcon in the field, we here adopt a novel approach to test the division‐of‐labor theory by using a detailed physics‐based flight simulator of birds. We study attacks by male and female Peregrine Falcons on prey species ranging from small passerines to large ducks, testing how catch success relates to the flight performance of predator and prey. Males prove to be better than females at catching highly maneuverable prey in level flight, but the catch success of both sexes improves and becomes more similar when diving, because of the higher aerodynamic forces that are available to both sexes for maneuvering in high‐speed flight. The higher maximum roll acceleration of the male Peregrine Falcon explains its edge over the female in catching maneuverable prey in level flight. Overall, catch success is more strongly influenced by the differences in maneuverability that exist between different species of prey than between the different sexes of falcon. On the other hand, the female can carry up to 50% greater loads than the male. More generally, our detailed simulation approach highlights the importance of several previously overlooked features of attack and escape. In particular, we find that it is not the prey's instantaneous maximum centripetal acceleration but the prey's ability to sustain a high centripetal acceleration for an extended period of time that is the primary driver of the variation in catch success across species.

opencc-zeroDec 2017View details →

Data from: Mechanical power curve measured in the wake of pied flycatchers indicate modulation of parasite power across flight speeds

How aerodynamic power required for animal flight varies with flight speed determines optimal speeds during foraging and migratory flight. Despite its relevance, aerodynamic power provide an elusive quantity to measure directly in animal flight. Here we determine the aerodynamic power from wake velocity fields, measured using tomographical particle image velocimetry, of pied flycatchers flying freely in a wind tunnel. We find a shallow U-shaped power curve, which is flatter than expected by theory. Based on how the birds vary body angle with speed, we speculate that the shallow curve result from increased body drag coefficient and body frontal area at lower flight speeds. Including modulation of body drag in the model results in a more reasonable fit with data than the traditional model. From the wake structure we also find a single starting vortex generated from the two wings during the downstroke across flight speeds (1-9 m/s). This is accomplished by the arm wings interacting at the beginning of the downstroke, generating a unified starting vortex above the body of the bird. We interpret this as a mechanism resulting in uniform downwash and low induced power, which can help explain the higher aerodynamic performance in birds compared to bats.

publicJan 2019View details →

Data from: Mechanical power curve measured in the wake of pied flycatchers indicate modulation of parasite power across flight speeds

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