Career
Oort was in charge of the bird collections at the Rijksmuseum of Natural History in Leiden. In 1915 he was made Director of this museum, a position which he held until his death. He was the author of Ornithologia Neerlandica, de vogels van Nederland (1922-1935), with plates by Marinus Adrianus Koekkoek (1873-1944).
These plates were later licensed by Harry Witherby for use in The Handbook of British Birds (1938-1941).