Publications by authors named "Kenneth P Dial"

25 Publications

  • Page 1 of 1

Waxing and Waning of Wings.

Trends Ecol Evol 2021 May 27;36(5):457-470. Epub 2021 Feb 27.

Department of Biological Sciences, California State University Los Angeles, Los Angeles, CA 90032, USA.

A major challenge to Darwinian evolution is explaining 'rudimentary' organs. This is particularly relevant to birds: rudimentary wings occur in fossils, as well as in developing, molting, and flight-impaired birds. Evidence shows that young birds flap small wings to improve locomotion and transition to flight. Although small wings also occur in adults, their potential role in locomotion is rarely considered. Here we describe the prevalence of rudimentary wings in extant birds, and how wings wax and wane on many timescales. This waxing and waning is integral to the avian clade and offers a rich arena for exploring links between form, function, performance, behavior, ecology, and evolution. Although our understanding is nascent, birds clearly show that rudimentary structures can enhance performance and survival.
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http://dx.doi.org/10.1016/j.tree.2021.01.006DOI Listing
May 2021

Age and performance at fledging are a cause and consequence of juvenile mortality between life stages.

Sci Adv 2018 06 20;4(6):eaar1988. Epub 2018 Jun 20.

Field Research Station at Fort Missoula, Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.

Should they stay or should they leave? The age at which young transition between life stages, such as living in a nest versus leaving it, differs among species and the reasons why are unclear. We show that offspring of songbird species that leave the nest at a younger age have less developed wings that cause poorer flight performance and greater mortality after fledging. Experimentally delayed fledging verified that older age and better developed wings provide benefits of reduced juvenile mortality. Young are differentially constrained in the age that they can stay in the nest and enjoy these fitness benefits because of differences among species in opposing predation costs while in the nest. This tension between mortality in versus outside of the nest influences offspring traits and performance and creates an unrecognized conflict between parents and offspring that determines the optimal age to fledge.
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http://dx.doi.org/10.1126/sciadv.aar1988DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6010335PMC
June 2018

Ontogeny of Flight Capacity and Pectoralis Function in a Precocial Ground Bird (Alectoris chukar).

Integr Comp Biol 2017 08;57(2):217-230

Field Research Station at Fort Missoula, Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.

Synopsis: Flight is the defining characteristic of birds, yet the mechanisms through which flight ability develops are only beginning to be understood. Wing-assisted incline running (WAIR) and controlled flapping descent (CFD) are behaviors that may offer significant adaptive benefits to developing birds. Recent research into these forms of locomotion has focused on species with precocial development, with a particularly rich data set from chukar partridge (Alectoris chukar). Here we briefly review the kinematics and aerodynamics of flight development in this species. We then present novel measurements of the development of pectoralis contractile behavior during the ontogenetic transition toward powered flight. To obtain these new empirical data, we used indwelling electromyography (EMG) and sonomicrometry and tested WAIR and CFD in seven age classes of chukar (n = 2-4 birds per age) from 5 days post hatching (dph) to adult (300+ dph). For each age class, we measured muscle activity during maximal performance, which was WAIR at 65° in birds 5 dph, CFD in birds 9 dph, WAIR at 80° in birds 14 dph, level flight in birds 25-61 dph, and ascending flight in adults. We also measured muscle activity during sub-maximal performance in all age classes. Flapping chukar chicks use near-continuous activation of their pectoralis at relatively low electromyography amplitudes for the first 8 days and progress to stereotypic higher-amplitude activation bursts by Day 12. The pectoralis undergoes increasing strain at higher strain rates with age, and length trajectory becomes more asymmetrical with greater variation in contractile velocity within the shortening phase of individual contractions. At 20-25 days (12-15% adult chukar mass), pectoralis activity and locomotor performance approaches that of adults, although strain rate exhibits a temporary decrease at 61 dph concurrent with using newly-replaced primary feathers. To better understand how these patterns relate to the evolution of life-history strategy and locomotion, we encourage future efforts to explore these behaviors in altricial and semi-altricial bird species.
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http://dx.doi.org/10.1093/icb/icx050DOI Listing
August 2017

Flapping before Flight: High Resolution, Three-Dimensional Skeletal Kinematics of Wings and Legs during Avian Development.

PLoS One 2016 21;11(4):e0153446. Epub 2016 Apr 21.

Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, Montana 59812, United States of America.

Some of the greatest transformations in vertebrate history involve developmental and evolutionary origins of avian flight. Flight is the most power-demanding mode of locomotion, and volant adult birds have many anatomical features that presumably help meet these demands. However, juvenile birds, like the first winged dinosaurs, lack many hallmarks of advanced flight capacity. Instead of large wings they have small "protowings", and instead of robust, interlocking forelimb skeletons their limbs are more gracile and their joints less constrained. Such traits are often thought to preclude extinct theropods from powered flight, yet young birds with similarly rudimentary anatomies flap-run up slopes and even briefly fly, thereby challenging longstanding ideas on skeletal and feather function in the theropod-avian lineage. Though skeletons and feathers are the common link between extinct and extant theropods and figure prominently in discussions on flight performance (extant birds) and flight origins (extinct theropods), skeletal inter-workings are hidden from view and their functional relationship with aerodynamically active wings is not known. For the first time, we use X-ray Reconstruction of Moving Morphology to visualize skeletal movement in developing birds, and explore how development of the avian flight apparatus corresponds with ontogenetic trajectories in skeletal kinematics, aerodynamic performance, and the locomotor transition from pre-flight flapping behaviors to full flight capacity. Our findings reveal that developing chukars (Alectoris chukar) with rudimentary flight apparatuses acquire an "avian" flight stroke early in ontogeny, initially by using their wings and legs cooperatively and, as they acquire flight capacity, counteracting ontogenetic increases in aerodynamic output with greater skeletal channelization. In conjunction with previous work, juvenile birds thereby demonstrate that the initial function of developing wings is to enhance leg performance, and that aerodynamically active, flapping wings might better be viewed as adaptations or exaptations for enhancing leg performance.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0153446PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4872793PMC
February 2017

Wings versus legs in the avian bauplan: development and evolution of alternative locomotor strategies.

Evolution 2015 Feb 19;69(2):305-20. Epub 2015 Jan 19.

Structure and Motion Laboratory, Royal Veterinary College, Hatfield, Hertfordshire AL97TA, United Kingdom.

Wings have long been regarded as a hallmark of evolutionary innovation, allowing insects, birds, and bats to radiate into aerial environments. For many groups, our intuitive and colloquial perspective is that wings function for aerial activities, and legs for terrestrial, in a relatively independent manner. However, insects and birds often engage their wings and legs cooperatively. In addition, the degree of autonomy between wings and legs may be constrained by tradeoffs, between allocating resources to wings versus legs during development, or between wing versus leg investment and performance (because legs must be carried as baggage by wings during flight and vice versa). Such tradeoffs would profoundly affect the development and evolution of locomotor strategies, and many related aspects of animal ecology. Here, we provide the first evaluation of wing versus leg investment, performance and relative use, in birds-both across species, and during ontogeny in three precocial species with different ecologies. Our results suggest that tradeoffs between wing and leg modules help shape ontogenetic and evolutionary trajectories, but can be offset by recruiting modules cooperatively. These findings offer a new paradigm for exploring locomotor strategies of flying organisms and their extinct precursors, and thereby elucidating some of the most spectacular diversity in animal history.
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http://dx.doi.org/10.1111/evo.12576DOI Listing
February 2015

Three-dimensional, high-resolution skeletal kinematics of the avian wing and shoulder during ascending flapping flight and uphill flap-running.

PLoS One 2013 15;8(5):e63982. Epub 2013 May 15.

Department of Biology, Providence College, Providence, Rhode Island, United States of America.

Past studies have shown that birds use their wings not only for flight, but also when ascending steep inclines. Uphill flap-running or wing-assisted incline running (WAIR) is used by both flight-incapable fledglings and flight-capable adults to retreat to an elevated refuge. Despite the broadly varying direction of travel during WAIR, level, and descending flight, recent studies have found that the basic wing path remains relatively invariant with reference to gravity. If so, joints undergo disparate motions to maintain a consistent wing path during those specific flapping modes. The underlying skeletal motions, however, are masked by feathers and skin. To improve our understanding of the form-functional relationship of the skeletal apparatus and joint morphology with a corresponding locomotor behavior, we used XROMM (X-ray Reconstruction of Moving Morphology) to quantify 3-D skeletal kinematics in chukars (Alectoris chukar) during WAIR (ascending with legs and wings) and ascending flight (AF, ascending with wings only) along comparable trajectories. Evidence here from the wing joints demonstrates that the glenohumeral joint controls the vast majority of wing movements. More distal joints are primarily involved in modifying wing shape. All bones are in relatively similar orientations at the top of upstroke during both behaviors, but then diverge through downstroke. Total excursion of the wing is much smaller during WAIR and the tip of the manus follows a more vertical path. The WAIR stroke appears "truncated" relative to ascending flight, primarily stemming from ca. 50% reduction in humeral depression. Additionally, the elbow and wrist exhibit reduced ranges of angular excursions during WAIR. The glenohumeral joint moves in a pattern congruent with being constrained by the acrocoracohumeral ligament. Finally, we found pronounced lateral bending of the furcula during the wingbeat cycle during ascending flight only, though the phasic pattern in chukars is opposite of that observed in starlings (Sturnus vulgaris).
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0063982PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3655074PMC
January 2014

From extant to extinct: locomotor ontogeny and the evolution of avian flight.

Trends Ecol Evol 2012 May 1;27(5):296-305. Epub 2012 Feb 1.

Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.

Evolutionary transformations are recorded by fossils with transitional morphologies, and are key to understanding the history of life. Reconstructing these transformations requires interpreting functional attributes of extinct forms by exploring how similar features function in extant organisms. However, extinct-extant comparisons are often difficult, because extant adult forms frequently differ substantially from fossil material. Here, we illustrate how postnatal developmental transitions in extant birds can provide rich and novel insights into evolutionary transformations in theropod dinosaurs. Although juveniles have not been a focus of extinct-extant comparisons, developing juveniles in many groups transition through intermediate morphological, functional and behavioral stages that anatomically and conceptually parallel evolutionary transformations. Exploring developmental transitions may thus disclose observable, ecologically relevant answers to long puzzling evolutionary questions.
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http://dx.doi.org/10.1016/j.tree.2011.12.003DOI Listing
May 2012

The broad range of contractile behaviour of the avian pectoralis: functional and evolutionary implications.

J Exp Biol 2011 Jul;214(Pt 14):2354-61

Field Research Station at Fort Missoula, Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.

Wing-assisted incline running (WAIR) in birds combines the use of the wings and hindlimbs to ascend otherwise insurmountable obstacles. It is a means of escape in precocial birds before they are able to fly, and it is used by a variety of juvenile and adult birds as an alternative to flight for exploiting complex three-dimensional environments at the interface of the ground and air. WAIR and controlled flapping descent (CFD) are the bases of the ontogenetic-transitional wing hypothesis, wherein WAIR and CFD are proposed to be extant biomechanical analogs for incremental adaptive stages in the evolutionary origin of flight. A primary assumption of the hypothesis is that work and power requirements from the primary downstroke muscle, the pectoralis, incrementally increase from shallow- to steep-angled terrestrial locomotion, and between terrestrial and aerial locomotion. To test this assumption, we measured in vivo force, electromyographic (EMG) activity and length change in the pectoralis of pigeons (Columba livia) as the birds engaged in shallow and steep WAIR (65 and 85 deg, respectively) and in three modes of slow flight immediately following take-off: ascending at 80 deg, level and descending at -60 deg. Mean EMG amplitude, muscle stress, strain, work and power were minimal during shallow WAIR and increased stepwise from steep WAIR to descending flight and level flight to reach the highest levels during ascending flight. Relative to resting length of the pectoralis, fractional lengthening (maximum muscle strain) was similar among behaviors, but fractional shortening (minimum muscle strain) was absent during WAIR such that the pectoralis did not shorten to less than the resting length. These data dramatically extend the known range of in vivo contractile behavior for the pectoralis in birds. We conclude that WAIR remains a useful extant model for the evolutionary transition from terrestrial to aerial locomotion in birds because work and power requirements from the pectoralis increase incrementally during WAIR and from WAIR to flight.
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http://dx.doi.org/10.1242/jeb.052829DOI Listing
July 2011

Ontogeny of lift and drag production in ground birds.

J Exp Biol 2011 Mar;214(Pt 5):717-25

Field Research Station at Fort Missoula, Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.

The juvenile period is often a crucial interval for selective pressure on locomotor ability. Although flight is central to avian biology, little is known about factors that limit flight performance during development. To improve understanding of flight ontogeny, we used a propeller (revolving wing) model to test how wing shape and feather structure influence aerodynamic performance during development in the precocial chukar partridge (Alectoris chukar, 4 to >100 days post hatching). We spun wings in mid-downstroke posture and measured lift (L) and drag (D) using a force plate upon which the propeller assembly was mounted. Our findings demonstrate a clear relationship between feather morphology and aerodynamic performance. Independent of size and velocity, older wings with stiffer and more asymmetrical feathers, high numbers of barbicels and a high degree of overlap between barbules generate greater L and L:D ratios than younger wings with flexible, relatively symmetrical and less cohesive feathers. The gradual transition from immature feathers and drag-based performance to more mature feathers and lift-based performance appears to coincide with ontogenetic transitions in locomotor capacity. Younger birds engage in behaviors that require little aerodynamic force and that allow D to contribute to weight support, whereas older birds may expand their behavioral repertoire by flapping with higher tip velocities and generating greater L. Incipient wings are, therefore, uniquely but immediately functional and provide flight-incapable juveniles with access to three-dimensional environments and refugia. Such access may have conferred selective advantages to theropods with protowings during the evolution of avian flight.
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http://dx.doi.org/10.1242/jeb.051177DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3036546PMC
March 2011

Scaling of mechanical power output during burst escape flight in the Corvidae.

J Exp Biol 2011 Feb;214(Pt 3):452-61

Flight Laboratory, Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA.

Avian locomotor burst performance (e.g. acceleration, maneuverability) decreases with increasing body size and has significant implications for the survivorship, ecology and evolution of birds. However, the underlying mechanism of this scaling relationship has been elusive. The most cited mechanistic hypothesis posits that wingbeat frequency alone limits maximal muscular mass-specific power output. Because wingbeat frequency decreases with body size, it may explain the often-observed negative scaling of flight performance. To test this hypothesis we recorded in vivo muscular mechanical power from work-loop mechanics using surgically implanted sonomicrometry (measuring muscle length change) and strain gauges (measuring muscle force) in four species of Corvidae performing burst take-off and vertical escape flight. The scale relationships derived for the four species suggest that maximum muscle-mass-specific power scales slightly negatively with pectoralis muscle mass (M(-0.18)(m), 95% CI: -0.42 to 0.05), but less than the scaling of wingbeat frequency (M(-0.29)(m), 95% CI: -0.37 to -0.23). Mean muscle stress was independent of muscle mass (M(-0.02)(m), 95% CI: -0.20 to 0.19), but total muscle strain (percent length change) scaled positively (M(0.12)(m), 95% CI: 0.05 to 0.18), which is consistent with previous results from ground birds (Order Galliformes). These empirical results lend minimal support to the power-limiting hypothesis, but also suggest that muscle function changes with size to partially compensate for detrimental effects of size on power output, even within closely related species. Nevertheless, additional data for other taxa are needed to substantiate these scaling patterns.
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http://dx.doi.org/10.1242/jeb.046789DOI Listing
February 2011

When hatchlings outperform adults: locomotor development in Australian brush turkeys (Alectura lathami, Galliformes).

Proc Biol Sci 2011 Jun 3;278(1712):1610-6. Epub 2010 Nov 3.

The University of Montana, Missoula, MT 59812, USA.

Within Galliformes, megapods (brush turkey, malleefowl, scrubfowl) exhibit unique forms of parental care and growth. Hatchlings receive no post-hatching parental care and exhibit the most exaggerated precocial development of all extant birds, hatching with fully developed, flight-capable forelimbs. Rather than flying up to safety, young birds preferentially employ wing-assisted incline running. Newly hatched Australian brush turkeys (Alectura lathami) are extraordinarily proficient at negotiating all textured inclined surfaces and can flap-walk up inclines exceeding the vertical. Yet, as brush turkeys grow, their forelimb-dependent locomotor performance declines. In an attempt to elucidate how hatchlings perform so well, we analysed hindlimb forces and forelimb kinematics. We measured ground reaction forces (GRFs) for animals spanning the entire growth range (110-2000 g) as they ascended a variably positioned inclined ramp that housed a forceplate. These data are compared with a similar dataset for a chukar partridge (Alectoris chukar) that exhibit a growth strategy typical of most other Galliformes and that demonstrate improved incline performance with increasing age. The brush turkeys' ontogenetic decline in incline running performance is accompanied by loss of traction at steep angles, reduced GRFs and increased wing-loading. We hypothesize that Australian brush turkeys, in contrast to other Galliformes, develop from forelimb-dominated young that exploit a variable terrain (e.g. mound nests, boulders, embankments, cliffs, bushes and trees) into hindlimb-dominated adults dependent on size and running speed to avoid predation.
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http://dx.doi.org/10.1098/rspb.2010.1984DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3081770PMC
June 2011

Scientific rotoscoping: a morphology-based method of 3-D motion analysis and visualization.

J Exp Zool A Ecol Genet Physiol 2010 Jun;313(5):244-61

Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912, USA.

Three-dimensional skeletal movement is often impossible to accurately quantify from external markers. X-ray imaging more directly visualizes moving bones, but extracting 3-D kinematic data is notoriously difficult from a single perspective. Stereophotogrammetry is extremely powerful if bi-planar fluoroscopy is available, yet implantation of three radio-opaque markers in each segment of interest may be impractical. Herein we introduce scientific rotoscoping (SR), a new method of motion analysis that uses articulated bone models to simultaneously animate and quantify moving skeletons without markers. The three-step process is described using examples from our work on pigeon flight and alligator walking. First, the experimental scene is reconstructed in 3-D using commercial animation software so that frames of undistorted fluoroscopic and standard video can be viewed in their correct spatial context through calibrated virtual cameras. Second, polygonal models of relevant bones are created from CT or laser scans and rearticulated into a hierarchical marionette controlled by virtual joints. Third, the marionette is registered to video images by adjusting each of its degrees of freedom over a sequence of frames. SR outputs high-resolution 3-D kinematic data for multiple, unmarked bones and anatomically accurate animations that can be rendered from any perspective. Rather than generating moving stick figures abstracted from the coordinates of independent surface points, SR is a morphology-based method of motion analysis deeply rooted in osteological and arthrological data.
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http://dx.doi.org/10.1002/jez.588DOI Listing
June 2010

Precocial development of locomotor performance in a ground-dwelling bird (Alectoris chukar): negotiating a three-dimensional terrestrial environment.

Proc Biol Sci 2009 Oct 1;276(1672):3457-66. Epub 2009 Jul 1.

Flight Laboratory, Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA.

Developing animals are particularly vulnerable to predation. Hence, precocial young of many taxa develop predator escape performance that rivals that of adults. Ontogenetically unique among vertebrates, birds transition from hind limb to forelimb dependence for escape behaviours, so developmental investment for immediate gains in running performance may impair flight performance later. Here, in a three-dimensional kinematic study of developing birds performing pre-flight flapping locomotor behaviours, wing-assisted incline running (WAIR) and a newly described behaviour, controlled flapping descent (CFD), we define three stages of locomotor ontogeny in a model gallinaceous bird (Alectoris chukar). In stage I (1-7 days post-hatching (dph)) birds crawl quadrupedally during ascents, and their flapping fails to reduce their acceleration during aerial descents. Stage II (8-19 dph) birds use symmetric wing beats during WAIR, and in CFD significantly reduce acceleration while controlling body pitch to land on their feet. In stage III (20 dph to adults), birds are capable of vertical WAIR and level-powered flight. In contrast to altricial species, which first fly when nearly at adult mass, we show that in a precocial bird the major requirements for flight (i.e. high power output, wing control and wing size) convene by around 8 dph (at ca 5% of adult mass) and yield significant gains in escape performance: immature chukars can fly by 20 dph, at only about 12 per cent of adult mass.
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http://dx.doi.org/10.1098/rspb.2009.0794DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817185PMC
October 2009

Allometry of behavior.

Trends Ecol Evol 2008 Jul 22;23(7):394-401. Epub 2008 May 22.

Flight Laboratory, Division of Biological Sciences, 32 Campus Drive, The University of Montana, Missoula, MT 59812, USA.

The study of allometric and size scaling relationships is well developed in most biological fields, but lags behind in the area of animal behavior. Part of the reason for this deficit is that scaling relationships of behaviors tend to be inherently more 'noisy' than other biological scaling relationships. However, body size has a pervasive influence on the performance of animals in their environments. For example, the frequently strong relationship between power-to-mass ratios and locomotor performance means that smaller species and individuals enjoy superior locomotor performance (burst acceleration and maneuverability) than larger species, particularly within a clade. We suggest that these size-related functional influences on performance profoundly influence many aspects of animal behavior, such as how animals forage, fight, flee, perceive danger, respond to risk and interact with other individuals. We outline exciting avenues for research on the allometry of behavior by integrating scaling and functional perspectives.
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http://dx.doi.org/10.1016/j.tree.2008.03.005DOI Listing
July 2008

A fundamental avian wing-stroke provides a new perspective on the evolution of flight.

Nature 2008 Feb 23;451(7181):985-9. Epub 2008 Jan 23.

Flight Laboratory, Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, Montana 59812, USA.

The evolution of avian flight remains one of biology's major controversies, with a long history of functional interpretations of fossil forms given as evidence for either an arboreal or cursorial origin of flight. Despite repeated emphasis on the 'wing-stroke' as a necessary avenue of investigation for addressing the evolution of flight, no empirical data exist on wing-stroke dynamics in an experimental evolutionary context. Here we present the first comparison of wing-stroke kinematics of the primary locomotor modes (descending flight and incline flap-running) that lead to level-flapping flight in juvenile ground birds throughout development. We offer results that are contrary both to popular perception and inferences from other studies. Starting shortly after hatching and continuing through adulthood, ground birds use a wing-stroke confined to a narrow range of less than 20 degrees , when referenced to gravity, that directs aerodynamic forces about 40 degrees above horizontal, permitting a 180 degrees range in the direction of travel. Based on our results, we put forth an ontogenetic-transitional wing hypothesis that posits that the incremental adaptive stages leading to the evolution of avian flight correspond behaviourally and morphologically to transitional stages observed in ontogenetic forms.
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http://dx.doi.org/10.1038/nature06517DOI Listing
February 2008

Aerodynamics of wing-assisted incline running in birds.

J Exp Biol 2007 May;210(Pt 10):1742-51

Department of Biology, University of Portland, 5000 North Willamette Boulevard, Portland, OR 97203, USA.

Wing-assisted incline running (WAIR) is a form of locomotion in which a bird flaps its wings to aid its hindlimbs in climbing a slope. WAIR is used for escape in ground birds, and the ontogeny of this behavior in precocial birds has been suggested to represent a model analogous to transitional adaptive states during the evolution of powered avian flight. To begin to reveal the aerodynamics of flap-running, we used digital particle image velocimetry (DPIV) and measured air velocity, vorticity, circulation and added mass in the wake of chukar partridge Alectoris chukar as they engaged in WAIR (incline 65-85 degrees; N=7 birds) and ascending flight (85 degrees, N=2). To estimate lift and impulse, we coupled our DPIV data with three-dimensional wing kinematics from a companion study. The ontogeny of lift production was evaluated using three age classes: baby birds incapable of flight [6-8 days post hatching (d.p.h.)] and volant juveniles (25-28 days) and adults (45+ days). All three age classes of birds, including baby birds with partially emerged, symmetrical wing feathers, generated circulation with their wings and exhibited a wake structure that consisted of discrete vortex rings shed once per downstroke. Impulse of the vortex rings during WAIR was directed 45+/-5 degrees relative to horizontal and 21+/-4 degrees relative to the substrate. Absolute values of circulation in vortex cores and induced velocity increased with increasing age. Normalized circulation was similar among all ages in WAIR but 67% greater in adults during flight compared with flap-running. Estimated lift during WAIR was 6.6% of body weight in babies and between 63 and 86% of body weight in juveniles and adults. During flight, average lift was 110% of body weight. Our results reveal for the first time that lift from the wings, rather than wing inertia or profile drag, is primarily responsible for accelerating the body toward the substrate during WAIR, and that partially developed wings, not yet capable of flight, can produce useful lift during WAIR. We predict that neuromuscular control or power output, rather than external wing morphology, constrain the onset of flight ability during development in birds.
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http://dx.doi.org/10.1242/jeb.001701DOI Listing
May 2007

Does the metabolic rate-flight speed relationship vary among geometrically similar birds of different mass?

J Exp Biol 2007 Mar;210(Pt 6):1075-83

Flight Laboratory, Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA.

Based on aerodynamic considerations, the energy use-flight speed relationship of all airborne animals and aircraft should be U-shaped. However, measures of the metabolic rate-flight speed relationship in birds have been available since Tucker's pioneering experiments with budgerigars nearly forty years ago, but this classic work remains the only study to have found a clearly U-shaped metabolic power curve. The available data suggests that the energetic requirements for flight within this species are unique, yet the metabolic power curve of the budgerigar is widely considered representative of birds in general. Given these conflicting results and the observation that the budgerigar's mass is less than 50% of the next smallest species to have been studied, we asked whether large and small birds have metabolic power curves of different shapes. To address this question we measured the rates of oxygen uptake and wingbeat kinematics in budgerigars and cockatiels flying within a variable-speed wind tunnel. These species are close phylogenetic relatives, have similar flight styles, wingbeat kinematics, and are geometrically similar but have body masses that differ by a factor of two. In contrast to our expectations, we found the metabolic rate-flight speed relationship of both species to be acutely U-shaped. We also found that neither budgerigars nor cockatiels used their normal intermittent flight style while wearing a respirometric mask. We conclude that species size differences alone do not explain the previously unique metabolic power curve of the budgerigar; however, due to the absence of comparable data we cannot evaluate whether the mask-related kinematic response we document influences the metabolic rate-flight speed relationship of these parrots, or whether the energetics of flight differ between this and other avian clades.
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http://dx.doi.org/10.1242/jeb.02727DOI Listing
March 2007

Origin of flight: Could 'four-winged' dinosaurs fly?

Nature 2005 Nov;438(7066):E3; discussion E3-4

Museum of Paleontology, University of California, Berkeley, California 94720, USA.

Our understanding of the origin of birds, feathers and flight has been greatly advanced by new discoveries of feathered non-avian dinosaurs, but functional analyses have not kept pace with taxonomic descriptions. Zhang and Zhou describe feathers on the tibiotarsus of a new basal enantiornithine bird from the Early Cretaceous of China. They infer, as did Xu and colleagues from similar feathers on the small non-avian theropod Microraptor found in similar deposits, that these leg feathers had aerodynamic properties and so might have been used in some kind of flight.
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http://dx.doi.org/10.1038/nature04354DOI Listing
November 2005

Mechanics of wing-assisted incline running (WAIR).

J Exp Biol 2003 Dec;206(Pt 24):4553-64

Flight Laboratory, Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA.

A recently discovered locomotor behavior, wing-assisted incline running (WAIR), allows fully volant animals to 'run' up vertical obstacles. Such a task would appear to be especially formidable for bipeds, yet WAIR is used preferentially by ground-dwelling birds, specifically chukar partridge Alectoris chukar, to reach refugia. The basic locomotor mechanics that enable this behavior are not fully understood. For instance, are there functional differences at the level of the wing during WAIR and free flight, and do the hindlimbs actively participate in propulsion during WAIR? To investigate wing function during these activities we used accelerometry to compare the instantaneous whole-body acceleration during WAIR and ascending free flights at a similar climb angle. Throughout a substantial portion of the wingbeat cycle, chukars engaged in WAIR experienced an acceleration oriented towards the substrate, whereas during ascending free flights the acceleration of the center of mass was parallel to the direction of travel. We investigated whether the animals were using their hindlimbs for propulsion, rather than for some other function (e.g. to maintain balance), by measuring ground reaction forces (GRF) during bouts of WAIR. Estimates of the contribution of the hindlimbs towards the vertical external work done by the bird were 98 +/- 8% of the total at an incline of 60 degrees (the steepest angle that birds were able to negotiate without the use of their forelimbs). During vertical (90 degrees ) bouts of WAIR the hindlimb contribution was 37 +/- 5% of the total external work. Yet, the magnitude of the peak GRF at 90 degrees was 175% of the value generated during level walking, revealing that birds engaged in WAIR do generate sizeable hindlimb forces even during vertical ascents. These data support the hypothesis that forelimbs are enabling hindlimb function, and we argue that this represents a locomotor strategy which may have been used by proto-birds during the evolution of flight.
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http://dx.doi.org/10.1242/jeb.00673DOI Listing
December 2003

Wing-assisted incline running and the evolution of flight.

Authors:
Kenneth P Dial

Science 2003 Jan;299(5605):402-4

Flight Laboratory, Avian Studies Program, Division of Biological Sciences, University of Montana (UM), Missoula, MT 59812, USA.

Flapping wings of galliform birds are routinely used to produce aerodynamic forces oriented toward the substrate to enhance hindlimb traction. Here, I document this behavior in natural and laboratory settings. Adult birds fully capable of aerial flight preferentially employ wing-assisted incline running (WAIR), rather than flying, to reach elevated refuges (such as cliffs, trees, and boulders). From the day of hatching and before attaining sustained aerial flight, developing ground birds use WAIR to enhance their locomotor performance through improved foot traction, ultimately permitting vertical running. WAIR provides insight from behaviors observable in living birds into the possible role of incipient wings in feathered theropod dinosaurs and offers a previously unstudied explanation for the evolution of avian flight.
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http://dx.doi.org/10.1126/science.1078237DOI Listing
January 2003

FROM FROND TO FAN: ARCHAEOPTERYX AND THE EVOLUTION OF SHORT-TAILED BIRDS.

Evolution 1996 Oct;50(5):2037-2048

Division of Biological Sciences, University of Montana, Missoula, Montana, 59812.

Modern birds have extremely short tail skeletons relative to Archaeopteryx and nonavialian theropod dinosaurs. Long- and short-tailed birds also differ in the conformation of main tail feathers making up the flight surface: frond shaped in Archaeopteryx and fan shaped in extant fliers. Mechanisms of tail fanning were evaluated by electromyography in freely flying pigeons and turkeys and by electrical stimulation of caudal muscles in anesthetized birds. Results from these experiments reveal that the pygostyle, rectrices, rectricial bulbs, and bulbi rectricium musculature form a specialized fanning mechanism. Contrary to previous models, our data support the interpretation that the bulbi rectricium independently controls tail fanning; other muscles are neither capable of nor necessary for significant rectricial abduction. This bulb mechanism permits rapid changes in tail span, thereby allowing the exploitation of a wide range of lift forces. Isolation of the bulbs on the pygostyle effectively decouples tail fanning from fan movement, which is governed by the remaining caudal muscles. The tail of Archaeopteryx, however, differs from this arrangement in several important respects. Archaeopteryx probably had a limited range of lift forces and tight coupling between vertebral and rectricial movement. This would have made the tail of this primitive flier better suited to stabilization than maneuverability. The capacity to significantly alter lift and manipulate the flight surface without distortion may have been two factors favoring tail shortening and pygostyle development during avian evolution.
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http://dx.doi.org/10.1111/j.1558-5646.1996.tb03590.xDOI Listing
October 1996

LOCOMOTOR MODULES AND THE EVOLUTION OF AVIAN FLIGHT.

Evolution 1996 Feb;50(1):331-340

Division of Biological Sciences, University of Montana, Missoula, Montana, 59812.

The evolution of avian flight can be interpreted by analyzing the sequence of modifications of the primitive tetrapod locomotor system through time. Herein, we introduce the term "locomotor module" to identify anatomical subregions of the musculoskeletal system that are highly integrated and act as functional units during locomotion. The first tetrapods, which employed lateral undulations of the entire body and appendages, had one large locomotor module. Basal dinosaurs and theropods were bipedal and possessed a smaller locomotor module consisting of the hind limb and tail. Bird flight evolved as the superimposition of a second (aerial) locomotor capability onto the ancestral (terrestrial) theropod body plan. Although the origin of the wing module was the primary innovation, alterations in the terrestrial system were also significant. We propose that the primitive theropod locomotor module was functionally and anatomically subdivided into separate pelvic and caudal locomotor modules. This decoupling freed the tail to attain a new and intimate affiliation with the forelimb during flight, a configuration unique to birds. Thus, the evolution of flight can be viewed as the origin and novel association of locomotor modules. Differential elaboration of these modules in various lineages has produced the diverse locomotor abilities of modern birds.
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http://dx.doi.org/10.1111/j.1558-5646.1996.tb04496.xDOI Listing
February 1996

Neuromuscular organization and regional EMG activity of the pectoralis in the pigeon.

J Morphol 1993 Oct;218(1):43-57

Division of Biological Sciences, University of Montana, Missoula, Montana 59812.

In order to improve our understanding of the neuromuscular control of the most massive avian flight muscle, we studied the innervation pattern of the pigeon pectoralis. Nine primary branches from the rostral trunk and nine to ten branches from the caudal trunk of the pectoral nerve were identified by microdissection in ten pigeons. The region of muscle that each branch innervates was delineated by nerve stimulation studies (ten pigeons) and six regions were confirmed by glycogen depletion (ten pigeons). In pigeons, branches from the rostral nerve innervate the anterior 3/5 of the sternobrachialis (SB) head of the pectoralis and branches from the caudal trunk innervate the posterior 1/2 of the SB and all of the throacobrachials (TB). In the SB, individual branches of the rostral pectoral nerve innervate wedge-shaped muscle regions (each approximately 1.3 cm wide), collectively forming a fan shaped arrangement along the sternal carina. Adjacent muscle regions partially overlap at their boundaries. Within the thoracobrachialis (TB) head of the pectrolis, muscle regions are wider. There is a region in mid-SB-where the innervation territories of the rostral and caudal nerves oferlap. Electromyographic (EMG) activity patterns were recorded within ten of the identified muscle regions during take-off, level flapping flight, and landing. Onset of EMG activity and EMG intensity within various muscle regions exhibits significant differences both within a wingbeat cycle and among different modes of flight. The innervation pattern of the pectoralis presents the anatomical substrate for neuromuscular compartmentalization and differential EMG activity within the pectoralis may reflect sensory-motor partitioning. The extent to which the neuromuscular compartmentalization of the pectoralis corresponds to its ability to produce an array of force vectors to the wing awaits further more detailed biomechanical studies. © 1993 Wiley-Liss, Inc.
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http://dx.doi.org/10.1002/jmor.1052180104DOI Listing
October 1993

The functional anatomy of the shoulder in the European starling (Sturnus vulgaris).

J Morphol 1991 Mar;207(3):327-344

Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138.

The excursions of wing elements and the activity of eleven shoulder muscles were studied by cineradiography and electromyography in European starlings (Sturnus vulgaris) flying in a wind tunnel at speeds of 9-20 m s . At the beginning of downstroke the humerus is elevated 80-90° above horizontal, and both elbow and wrist are extended to 90° or less. During downstroke, protraction of the humerus (55°) remains constant; elbow and wrist are maximally extended (120° and 160°, respectively) as the humerus passes through a horizontal orientation. During the downstroke-upstroke transition humeral depression ceases (at about 20° below horizontal) and the humerus begins to retract. However, depression of the distal wing continues by rotation of the humerus and adduction of the carpometacarpus. Humeral retraction (to within about 30° of the body axis) is completed early in upstroke, accompanied by flexion of the elbow and carpometacarpus. Thereafter the humerus begins to protract as elevation continues. At mid-upstroke a rapid counterrotation of the humerus reorients the ventral surface of the wing to face laterad; extension of the elbow and carpometacarpus are initiated sequentially. The upstroke-downstroke transition is characterized by further extension of the elbow and carpometacarpus, and the completion of humeral protraction. Patterns of electromyographic activity primarily coincide with the transitional phases of the wingbeat cycle rather than being confined to downstroke or upstroke. Thus, the major downstroke muscles (pectoralis, coracobrachialis caudalis, sternocoracoideus, subscapularis, and humerotriceps) are activated in late upstroke to decelerate, extend, and reaccelerate the wing for the subsequent downstroke; electromyographic activity ends well before the downstroke is completed. Similarly, the upstroke muscles (supracoracoideus, deltoideus major) are activated in late downstroke to decelerate and then reaccelerate the wing into the upstroke; these muscles are deactivated by mid-upstroke. Only two muscles (scapulohumeralis caudalis, scapulotriceps) exhibit electromyographic activity exclusively during the downstroke. Starlings exhibit a functional partitioning of the two heads of the triceps (the humerotriceps acts with the pectoralis group, and does not overlap with the scapulotriceps). The biphasic pattern of the biceps brachii appears to correspond to this partitioning.
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http://dx.doi.org/10.1002/jmor.1052070309DOI Listing
March 1991

Three sympatric species of Neotoma: dietary specialization and coexistence.

Authors:
Kenneth P Dial

Oecologia 1988 Sep;76(4):531-537

Department of Biological Sciences, Northern Arizona University, 86011, Flagstaff, AZ, USA.

Three sympatric species of Neotoma occur in the southern Great Basin Desert in northern Arizona. Observations and experiments from 1980-1984 focused on diet and den selection to determine to what extent woodrats partition available food and shelter. Analyses included microscopic inspection of feces from live-trapped animals, forage moisture content, and seasonal habitat utilization. Each species of woodrat was found to selectively forage on a different genus of the three evergreens on the study site: N. albigula was the only species to eat appreciable amounts of Yucca, while N. devia, specialized on Ephedra epidermis, and N. stephensi on Juniperus. Observations in the laboratory showed a linear dominance hierarchy where the larger species dominated smaller ones, i.e., N. albigula>N. stephensi>N. devia. To determine if such a hierarchy existed in the field, the behaviorally dominant species (N. albigula and N. stephensi) were continually removed (from a 25 ha experimental plot) over a 12-month period leaving only the subordinate species (N. devia) in the area. In these experiments, 40% of the "dominant"-species dens became occupied by 20 of the "subordinate"-species on the removal plot, whereas there were no interspecific den site (n=39) changes among species on the control plot. Removal of the two dominant Neotoma spp resulted in an increase of N. devia from a pre-removal high of 16 to a post-removal population of 26 individuals. These data suggest that while these woodrats may not compete for food, the subordinate species compete with the dominant species for den sites, prime dens being sequestered by the behaviorally dominant species.
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http://dx.doi.org/10.1007/BF00397865DOI Listing
September 1988