Meeting Abstract

12.2  Friday, Jan. 4  Dabbling, grazing and diving: Skull shape is related to beak foraging behaviors in the avian order Anseriformes OLSEN, AM*; WESTNEAT, MW; University of Chicago, IL; Field Museum of Natural History, Chicago, IL aolsen@uchicago.edu

Anseriforms, the avian order that includes ducks, geese, swans and mergansers have a diversity of beak shapes and foraging behaviors, including grazing, diving and dabbling. This morphological diversity is not limited to the beak, however. Posterior to the upper bill, lie kinetic (mobile) cranial bones that enable rotation of the upper bill relative to the braincase (cranial kinesis) and these bones also have diverse morphologies. Given that these bones transmit force to the upper bill and given the diverse functional requirements of beaks among anseriforms we tested whether the morphological diversity of these bones is explained by the efficiency with which different morphologies transmit force or motion to the upper bill. We collected 3D morphometric data from more than 80 specimens representing more than 30 genera in Anseriformes. Using a custom static force model, we predicted the torque at the upper bill given an input torque to the quadrate. Within Anseriformes, upper bill-quadrate torque transmission ranged from 0.93 to 1.87, where lower values correspond to displacement amplification and higher values correspond to force amplification. Additionally, grouped by foraging behavior, dabblers have lower torque transmission values than grazers and deep divers. Thus, we find support for our hypothesis: anseriforms with foraging behaviors expected to require more force (grazers and deep divers) have linkage morphologies that more efficiently transmit force through the linkage bones to the upper bill relative to anseriforms with beak behaviors expected to require continuous motion and lower force (dabblers).