Turtledove

The turtledove, like many other creatures in Suspendium-rich regions, has learned the trick of bio-accumulating Suspendium to become flighted. In the turtledove's case, the accumulation is confined to the shell, which as a rigid mass of bone acts as an excellent and safe matrix for the Suspendium. As a result, these animals are able to grow to large sizes while remaining afloat, using their elongated flippers to propel themselves.

Concept art for Airships: Conquer the Skies - www.zarkonnen.com/airships/

(Yes, I know there's a real animal called a turtledove.)