Functional significance of the uncinate processes in birds

Peter G. Tickle, A. Roland Ennos, Laura E. Lennox, Steven F. Perry, Jonathan R. Codd

    Research output: Contribution to journalArticlepeer-review


    The functional significance of the uncinate processes to the ventilatory mechanics of birds was examined by combining analytical modeling with morphological techniques. A geometric model was derived to determine the function of the uncinate processes and relate their action to morphological differences associated with locomotor specializations. The model demonstrates that uncinates act as levers, which improve the mechanical advantage for the forward rotation of the dorsal ribs and therefore lowering of the sternum during respiration. The length of these processes is functionally important; longer uncinate processes increasing the mechanical advantage of the Mm. appendicocostales muscle during inspiration. Morphological studies of four bird species showed that the uncinate process increased the mechanical advantage by factors of 2-4. Using canonical variate analysis and analysis of variance we then examined the variation in skeletal parameters in birds with different primary modes of locomotion (non-specialists, walking and diving). Birds clustered together in distinct groups, indicating that uncinate length is more similar in birds that have the same functional constraint, i.e. specialization to a locomotor mode. Uncinate processes are short in walking birds, long in diving species and of intermediate length in non-specialist birds. These results demonstrate that differences in the breathing mechanics of birds may be linked to the morphological adaptations of the ribs and rib cage associated with different modes of locomotion.
    Original languageEnglish
    Pages (from-to)3955-3961
    Number of pages6
    JournalJournal of Experimental Biology
    Issue number22
    Publication statusPublished - Nov 2007


    • Biomechanics
    • Breathing mechanics
    • Morphology
    • Uncinate


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