Relative forelimb-hindlimb investment is associated with flight style, foraging strategy, and nestling period, but not nest type

We investigated Dial’s 2003 hypothesis that birds that rely more heavily
upon flight as their primary mode of locomotion and thus invest more in
their forelimbs than hindlimbs will experience selection for smaller body
sizes, greater altriciality, and more complex nests. To test this
hypothesis, we examined the skeletons of over 2,000 individuals from 313
species representing the majority of avian families and all major branches
of the avian tree. We used the lengths of the sternal keel and long bones
of the wing relative to the lengths of the leg long bones as an index of
relative locomotor investment. We found that locomotor investment was
predicted by flight style, foraging method, and length of nestling period,
supporting Dial’s hypothesis. Soaring birds and birds with more acrobatic
flight styles, birds whose foraging methods were heavily reliant upon
flight, and whose young spent more time in the nest tended to invest more
in their forelimbs relative to hindlimbs. Nest type and body size were not
significant predictors of relative forelimb-hindlimb investment, however,
suggesting that the relationships among flight style, locomotor
investment, and life history are not as tightly intertwined as Dial
originally hypothesized.