Data and codes from: Flight hampers the evolution of weapons in birds

Birds are a remarkable example of how sexual selection can produce diverse
ornaments and behaviors. Specialized fighting structures like deer’s
antlers, in contrast, are mostly absent among birds. Here, we investigated
if the birds’ costly mode of locomotion — powered flight — helps explain
the scarcity of weapons among members of this clade. Our simulations of
flight energetics predicted that the cost of bony spurs — a specialized
avian weapon — should increase with time spent flying. Bayesian
phylogenetic comparative analyses using a global spur dataset corroborated
this prediction. First, extant species with flight-efficient wings (which
presumably fly more frequently) tend to have fewer or no bony spurs.
Second, this association likely arose because flying more leads to more
frequent evolutionary loss of spurs. Together, these findings suggest
that, much like pneumatic bones, absence of weaponry may be another
feature of the avian body plan that allows birds to efficiently explore
the aerial habitat.