Biology subjects

Tobalske, B. W.

Publications and source records attributed to Tobalske, B. W..

8 recordsLinked to original sources

bioRxiv2026

Tail Flaring as an Agonistic Signal in Hummingbirds

Bird tails in flight generate lift, reduce pressure drag, and stabilize pitch. Hummingbirds can sustain hovering in still air and generate lift in both the up- and downstroke due to their proportionally enormous primary flight muscles and derived wing skeleton. Given their mass-specific wing power, it is possible that tails are less essential to the aerodynamics of hummingbird flight than they are in other birds, freeing them for non-locomotor functions. Hummingbird tails are well known for their morphological elaboration as sexually selected ornaments, including sound generation. From informal observations of agonism, we hypothesized tail flaring may also be a visual signal used by males during fighting. To begin testing this, we measured the frequency and magnitude of tail flaring during fighting. We measured kinematics of tail flaring during male-male fighting of Calliope hummingbirds (Selasphorus calliope, n = 10) indoors. Consistent with our hypothesis, captive males exhibited greater angles of tail flare when engaged in a fight (34.6 {+/-} 45.5{degrees}, mean {+/-} sd) than when performing solitary landing (-14.2 {+/-} 9.12 {degrees}) and takeoff (-14.1 {+/-} 7.0 {degrees}) maneuvers. When birds won a fight, the angles of their tail spread were greater than when they lost (p = 0.01). Moreover, recordings of seven species of hummingbird in the field revealed 95% of inter- and intra- specific contests included tail flaring. We evaluate these results in the context of signaling during animal contests and propose future tests of whether tail flaring is an honest signal of individual quality and Resource Holding Potential. Summary StatementMale-male fighting is common in hummingbirds with competition over food and mates. During these competitions, tail flaring and waggle maneuvers are used as a signal of aggressive intent.

evolutionary biology↗

bioRxiv2023

Hummingbirds rapidly respond to the removal of vision and control a sequence of rate-commanded maneuvers in milliseconds

Hummingbird flight is the epitome of extreme aerial agility and controlled stability, as hummingbirds routinely exercise a variety of stunning aerobatic feats. Yet, the control of these amazing maneuvers is not well understood. Here we examined how hummingbirds control a sequence of maneuvers within milliseconds and tested whether and when their vision is active during this rapid process. We elicited escape flight in calliope hummingbirds and removed visible light at various instants during the maneuvers and quantified their flight kinematics and responses. We show that the escape maneuvers were composed of rapidly-controlled sequential modules, including evasion, reorientation, nose-down dive, forward flight, and nose-up to hover. The hummingbirds did not respond to the light removal during evasion and reorientation until a critical light-removal time; afterward they showed two categories of luminance-based responses that rapidly altered maneuvering modules to terminate the escape. We also show that hummingbird maneuvers are rate-commanded and require no active braking, i.e., their body angular velocities were proportional to the change of wing motion patterns, a trait that likely alleviates the computational demand on flight control. Together, this work uncovers the key traits of hummingbird agility, which can also inform and inspire designs for next-generation agile aerial systems.

animal behavior and cognition↗

bioRxiv2023

Hummingbirds use wing inertial effects to improve maneuverability

Hummingbirds outperform other birds in terms of aerial agility at low flight speeds. To reveal the key mechanisms that enable such unparalleled agility, we reconstructed body and wing motion of hummingbird escape maneuvers from high-speed videos; then, we performed computational fluid dynamics modeling and flight mechanics analysis, in which each wingbeat was resolved. We found that the birds utilized the inertia of their wings to achieve peak body rotational acceleration within half a wingbeat before the aerodynamic forces became dominant. The aerodynamic forces instead counteracted the reversed inertial forces in the other half wingbeat, thereby to sustain body rotation, albeit at a lower acceleration. Thus, individual wingbeat cycles that generated body rotations can be split into an agility phase with rapid inertial acceleration, and a stability phase with counteracting aerodynamic and inertial acceleration. This mechanism involving inertial steering enables hummingbirds to generate instantaneous body acceleration at any phase of a wingbeat, and it is likely the key to understanding the unique dexterity distinguishing them from aircraft that solely rely on aerodynamics for maneuvering.

animal behavior and cognition↗

bioRxiv2023

How small deviations in kinematics and body form dictate muscle performances in the finely tuned avian downstroke

Avian takeoff requires peak pectoralis muscle power to generate sufficient aerodynamic force during the downstroke. Subsequently the much smaller supracoracoideus recovers the wing during the upstroke. How the pectoralis work loop is tuned to power flight is unclear. We integrate wingbeat-resolved muscle, kinematic and aerodynamic recordings in vivo with a new mathematical model to disentangle how the pectoralis muscle overcomes wing inertia and generates aerodynamic force during takeoff in doves. Doves reduce the angle of attack of their wing mid-downstroke to efficiently generate aerodynamic force, resulting in an aerodynamic power dip, that allows transferring excess pectoralis power into tensioning the supracoracoideus tendon to assist the upstroke--improving the pectoralis work loop efficiency simultaneously. Integrating extant bird data, our model shows how the pectoralis of birds with faster wingtip speed need to generate proportionally more power. Finally, birds with disproportionally larger wing inertia need to activate the pectoralis earlier to tune their downstroke. Subject area in eLifeEcology Impact statementDoves improve their wingbeat efficacy without elevating maximum pectoralis power by angling their wings mid-downstroke to efficiently generate aerodynamic force while simultaneously tensioning the supracoracoideus tendon to assist the upstroke.

ecology↗

bioRxiv2022

Thermal acclimation in a non-migratory songbird occurs via changes to thermogenic capacity, but not conductance

Thermoregulatory performance can be modified through changes in various subordinate traits, including thermal conductance, basal and summit metabolic rates, and body composition. We investigated physiological differences between black-capped chickadees (Poecile atricapillus) acclimated for six weeks to cold (-5{degrees}C) or control (25{degrees}C) environments (n = 7 per treatment) by measuring traits that affect thermal balance. We made repeated measurements of basal and summit metabolic rates via flow-through respirometry and body composition using quantitative magnetic resonance of live birds. At the end of the acclimation, we measured thermal conductance of the combined feathers and skins. Cold-acclimated birds had a higher summit metabolic rate, reflecting a greater capacity for endogenous heat generation, and an increased lean mass. However, birds did not alter their thermal conductance. These results suggest that, while birds can use multiple mechanisms to acclimate to their thermal environment, they use a subset of potential changes over varying timescales.

physiology↗

bioRxiv2022

Three-dimensional actuation of hummingbird wings requires diverse effects from the primary flight muscles

Hummingbirds have evolved to hover and maneuver with exceptional flight control. This is directly enabled by their musculoskeletal system that successfully exploits the agile motion of flapping wings. Here, we reveal novel principles of hummingbird wing actuation that provide insights into the evolution and robotic emulation of hummingbird flight. We develop a functional model of hummingbird musculoskeletal system, which predicts instantaneous, three-dimensional torque produced by primary (pectoralis and supracoracoideus) and combined secondary muscles. It also reveals primary muscle contractile behavior, including stress, strain, elasticity, and work. Results show that the primary muscles (i.e., the flight "engine") function as diverse effectors, as they do not simply power the stroke, but also actively deviate and pitch the wing. The secondary muscles produce controlled-tightening effects, by acting against primary muscles in deviation and pitching. The diverse effector capacity of pectoralis is associated with the evolution of a comparatively enormous bicipital crest on humerus.

biophysics↗

bioRxiv2021

Multi-modal locomotor costs explain sexual size but not shape dimorphism in a leaf-mimicking insect

In most arthropods, adult females are larger than males, and male competition is a race to quickly locate and mate with scattered females (scramble competition polygyny). In this context, smaller males may be favored due to more efficient locomotion leading to higher mobility during mate searching while larger males may benefit from increased speed and higher survivorship. Understanding how body size affects different aspects of the locomotor performance of males is therefore essential to shed light on the evolution of this widespread mating system. Using a combination of empirical measures of flight performance and substrate adhesion, and modelling of body aerodynamics, we show that large body size impairs both flight and landing (attachment) performance in male leaf insects (Phyllium philippinicum), a species where relatively small and skinny males fly through the canopy in search of large sedentary females. Smaller males were more agile in the air, ascended more rapidly during flight, and had a lower risk of detaching from the substrates on which they walk and land. Our models revealed variation in body shape affected body lift and drag, but tradeoffs with weight meant that effects were negligible, suggesting that flight costs do not explain the evolution of strong sexual dimorphism in body shape in this species. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=177 SRC="FIGDIR/small/451325v1_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@193d0adorg.highwire.dtl.DTLVardef@1693bccorg.highwire.dtl.DTLVardef@1d50b53org.highwire.dtl.DTLVardef@1da8572_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2020

Body temperature maintenance acclimates in a winter-tenacious songbird

Flexibility in heat generation and dissipation mechanisms provides endotherms the ability to match their thermoregulatory strategy with external demands. However, the degree to which these two mechanisms account for seasonal changes in body temperature regulation is unexplored. Here we present novel data on the regulation of avian body temperature to investigate how birds alter mechanisms of heat production and heat conservation to deal with variation in ambient conditions. We subjected Dark-eyed Juncos (Junco hyemalis) to chronic cold acclimations of varying duration and subsequently quantified their metabolic rates, thermal conductance, and ability to maintain normothermia. Cold-acclimated birds adjusted traits related to both heat generation (increased summit metabolic rate) and heat conservation (decreased conductance) to improve their body temperature regulation. Increases in summit metabolic rate occurred rapidly, but plateaued after one week of cold exposure. In contrast, changes to conductance occurred only after nine weeks of cold exposure. Thus, the ability to maintain body temperature continued to improve throughout the experiment, but the mechanisms underlying this improvement changed through time. Our results demonstrate the ability of birds to adjust thermoregulatory strategies in response to thermal cues and reveal that birds may combine multiple responses to meet the specific demands of their environments.

physiology↗