He is remembered chiefly as the first ornithologist to propose a division of birds into Ratitae (ratites or running birds, with a flat sternum) and Carinatae (carinates or flying birds, with a keeled sternum), which formed part of his classification of birds in Tentamen Systematis Naturalis Avium, published in Berlin in 1816 (in Abhandlugen Akad. Wiss. Berlin 1812–1813: Phys. Kl.).