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Because he was so gracious to bring it up....

Habib, M. B. and C. B. Ruff. 2008. The effects of locomotion on the structural 
characteristics of avian limb bones. _Zoological Journal of the Linnaean 
Society_ 153(3):601â624.

Abstract:
  "Despite the wide range of locomotor adaptations in birds, little detailed 
attention has been given to the relationships between the quantitative 
structural characteristics of avian limb bones and bird behaviour. Possible 
differences in forelimb relative to hindlimb strength across species have been 
especially neglected. We generated cross-sectional, geometric data from 
peripheral quantitative computed tomography scans of the humerus and femur of 
127 avian skeletons, representing 15 species of extant birds in 13 families. 
The sample includes terrestrial runners, arboreal perchers, hindlimb-propelled 
divers, forelimb-propelled divers and dynamic soarers. The hindlimb-propelled 
diving class includes a recently flightless island form. Our results 
demonstrate that locomotor dynamics can be differentiated in most cases based 
on cross-sectional properties, and that structural proportions are often more 
informative than bone length proportions for determining
 behaviour and locomotion. Recently flightless forms, for example, are more 
easily distinguished using structural ratios than using length ratios. A proper 
phylogenetic context is important for correctly interpreting structural 
characteristics, especially for recently flightless forms. Some of the most 
extreme adaptations to mechanical loading are seen in aquatic forms. Penguins 
have forelimbs adapted to very high loads. Aquatic species differ from 
non-aquatic species on the basis of relative cortical thickness. The 
combination of bone structural strength and relative cortical area of the 
humerus successfully differentiates all of our locomotor groups. The methods 
used in this study are highly applicable to fossil taxa, for which morphology 
is known but behaviour is not. The use of bone structural characteristics is 
particularly useful in palaeontology not only because it generates strong 
signals for many locomotor guilds, but also because analysing such
 traits does not require knowledge of body mass, which can be difficult to 
estimate reliably for fossil taxa."