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The Allometry of Bird Flight Performance University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 2009 The allometry of bird flight performance Brandon Edward Jackson The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Jackson, Brandon Edward, "The allometry of bird flight performance" (2009). Graduate Student Theses, Dissertations, & Professional Papers. 960. https://scholarworks.umt.edu/etd/960 This Dissertation is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. THE ALLOMETRY OF BIRD FLIGHT PERFORMANCE By BRANDON EDWARD JACKSON B. A. Colgate University, Hamilton, NY, 1999 M. S. The University of Montana, Missoula, MT 2003 Dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Organsimal Biology and Ecology The University of Montana Missoula, MT December 2009 Approved by: Perry Brown, Associate Provost for Graduate Education Graduate School Kenneth P. Dial, Chair Division of Biological Sciences Thomas Martin Division of Biological Sciences Erick Greene Division of Biological Sciences James Jacobs Department of Physics and Astronomy Robert Dudley Department of Integrative Biology The University of California, Berkeley, CA Jackson, Brandon, Ph.D., December 2009 Organismal Biology and Ecology The allometry of bird flight performance Chairperson: Kenneth P. Dial Avian flight performance decreases with body size in birds, but previous work has been unable to define the underlying mechanism. Wingbeat frequency is hypothesized to ultimately constrain flight performance via muscular mechanical power output because frequency decreases with body size. I measured maximal burst take-off and vertical accelerating flight in 32 species of songbirds (Passeriformes), including the entire range of body mass in this clade (5-900 g). Jump forces against the ground were recorded with a forceplate. High-speed digital video captured the movement of morphological landmarks in order to estimate aerodynamic power requirements and dynamic morphology in flight. Surgically implanted gauges recorded the components of muscle power (muscle length change, force production, frequency) in the four largest species (Common raven, American crow, Black-billed magpie, and Gray jay). Flight performance and total aerodynamic power scaled with negative allometry, but were significantly influenced by foraging ecology. Species that forage on the ground had relatively lower jump impulses, shorter wings, higher wingbeat frequencies, and higher power output than species that forage on elevated substrates. I also found two unexpected internal scaling patterns. Both proportional muscle length change (muscle strain) and average cross-sectional area specific force (muscle stress) increased with size. Longer wingbeat cycles may permit more complete muscle activation in larger birds, thereby partially compensating for the constraint imposed by wingbeat frequency. These data offer the strongest support and the only direct evidence for power-limited scaling of flight performance to date. ii PREFACE You can drop a mouse down a thousand-yard mineshaft; and, on arriving at the bottom, it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes. ! "#$#%#&'()*(+,&-./0& 12+&3,4+5&67,&84576&94:,;& Body size is likely the single most influential phenotypic element for virtually all other aspects of an organism's biology. Schmidt-Nielsen (1984) argued that over 95% of any organism’s phenotype could be predicted knowing only its phylogenetic placement and its body mass. It was this idea that first piqued my interest in the study of allometry. As any scientist, or any inquisitive five-year old, would follow such a statement, I wondered “Why?” Despite the countless life-history, physiological, and morphological traits that vary with body-size (e.g. Hill 1950; Greenewalt 1962; Schmidt-Nielsen 1984; Calder 1996), the underlying mechanisms behind these correlations tend to be subjects of much debate. Additionally, size has been suggested as both a target of selection, particularly sexual selection (e.g. Andersson & Iwasa 1996), and as influencing evolutionary patterns (e.g. diversification rates within clades, Dial & Marzluff 1989). Given the importance of body size to evolutionary biology and ecology a number of significant questions remain unanswered. Why are animals a given size? Why does a clade have specific minimum and maximum sizes? How does natural or sexual selection act on size? Birds in particular demonstrate interesting patterns in size. They are the most speciose clade among tetrapod vertebrates, a factor that is typically attributed to their ability to fly and exploit novel niches unavailable to most ground based organisms. Yet iii the largest of the extant flying species, within several divergent avian orders, are all ~13- 15 kg (Kori bustard, Mute swan, Wild turkey). Among volant bird species it has been suggested anecdotally, but minimally quantified, that flight ability varies inversely with body size. Very large birds appear to have difficulty taking off, and have restricted aerial behavior. Restrictions on flight performance increase with size until ~15 kg, when they become too great to allow even steady flight. Similar locomotor restrictions likely influence the upper size limit within other clades, but flight is so costly that body-size induced limitations should be much more observable in birds. At least two hypotheses attempt to explain the scaling of flight performance ability, but neither has been fully tested. The first (and generally accepted) hypothesis suggests that relative muscle power decreases with size since wing-beat frequency also decreases (Pennycuick 1975). At some size, large birds with large (long) wings cannot produce enough muscle power to overcome the effects of drag and gravity, and flight is thus impossible. The second hypothesis suggests that relative muscle power is invariable with size, but the ability to produce actual lift from a given amount of power decreases with size (Marden 1994). Under this hypothesis, birds (and any flying organism) would not be restricted at 15 kg if a large enough proportion of their body mass was composed of flight muscle. Not only has the pattern of scaling of flight performance remained un- quantified, neither hypothesis attempting to explain it has previously been tested in a large and ecologically diverse sample of species. This collection of work sets out as an initial examination of the influence of body size on avian burst locomotor abilities. It approaches three main questions: Does flight performance ability vary with body size among bird species? What morphological and iv physiological mechanisms explain such variation? And what are the ecological and evolutionary consequences of variation of flight performance with size in birds? Herein I present three chapters written for various journals, each with a unique focus on one or more of the aforementioned questions. Chapter 1 reports on the actual performance abilities of a survey of passerines, spanning from 5 g Ruby-crowned kinglets to an 898 g Common raven, which represent the entire extant body-mass range of the most speciose avian order (Passeriformes). While I demonstrate that flight performance scales negatively, in passerines size is not the entire story. Elements of ecology and morphological allometry confound the size-performance relationship. Chapter 2 discusses the mechanics of burst takeoff and vertical flight (hindlimb contribution, forelimb and body kinematics, estimates of total muscle power output). Surprisingly, despite large variation in ecology, size, phylogeny, and performance, most of the species used relatively similar and invariant kinematics. Having established that there is some size-performance relationship and that variation in kinematics and hindlimb contributions can not explain it, Chapter 3 goes to the heart of the matter by examining in vivo muscle function in four species of corvids during burst vertical flight. The two outstanding hypotheses make divergent predictions about the scaling of mass-specific power output from the muscles, and the in vivo techniques in Chapter 3 are the only available ways of assessing actual muscle power. v References <+*,899=+>&?#&@&AB(9(>&C#&-..D&%,EF()&9,),G64=+#&!"#$%&'($')*+,+-.'/')0+,12(+$&!!>& HI!H0#&J*=4K-L#-L-DML-D.!HINOJ.DP0-LN/!-P#& & Q()*,8>&R#<#&-..D&3(4#5'61$*2(+$5'7$%'8(9#':(&2+".>&S=T,8&UF3)4G(64=+9#& & S4()>&V#U#&@&?(8:)FWW>&"#?#&-.0.&X=+8(+*=Y&S4T,894W4G(64=+&B4674+&Z(E=+=Y4G& <99,Y3)(5,9#&3.&2#;72(*'<++,+-.&"#>&/D!IO#& & [8,,+,B()6>&Q#'#&-.D/&=(;#$&(+$7,'"#,72(+$&>(?&'9+"'9,.($-'7$(;7,&>&%Y4679=+4(+& A+9646F64=+#& & '()*(+,>&"#$#%#&-./0&2+&3,4+5&67,&84576&94:,#&@'2"#7&1".'+9'&*(#$*#>&I/-–I/H#& & '4))>&<#\#&-.HL&Z7,&*4Y,+94=+9&=W&(+4Y()9&(+*&67,48&YF9GF)(8&*]+(Y4G9#&3*(A'B"+-&"#>& /L.!/IL#& & ?(8*,+>&"#'#&-..N&^8=Y&*(Y9,)W)4,9&6=&_6,8=9(F89K&7=B&3F896&(+*&9F96(4+(3),&W)4576& _,8W=8Y(+G,&9G(),&B467&94:,#&@;'C'B>.&(+,'D#-1,'E$2#-"'F+;?'B>.&(+,&$%%>& `-LOO!-L0N#& & U,++]GF4Ga>&Q#"#&-.OH&?,G7(+4G9&=W&W)4576#&@0(7$'G(+,+-.&&>&-–OH#&
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