Feet of rails and grebes move efficiently through water thanks to toes with lobes that fold back on the forward stroke.

   
  "American coots and other rails, and species of grebes are able to swim without webbed feet because their toes have lobes that open on the down stroke but fold flat on the recovery stroke. These lobes also help the birds walk on wetland vegetation and mud." (van der Valk 2006:73-74)
  Learn more about this functional adaptation.