Like many other fossils from the Green River Formation, its are exceptionally well preserved, bearing impressions of skin and feathers.

[2] The original specimen of Calciavis, AMNH 30578, was found in the Fossil Butte Member of the Green River Formation, Wyoming, dating to around 51 million years ago.

It is diagnosed by several features of the skull and pelvis as well as having metatarsals IV and II subequal in distal extent.

It differs from the contemporary Pseudocrypturus by a shorter skull - in Calciavis the skull is shorter than the humerus, while in inverse happens in Pseudocrypturus -, as well as a proportionally narrower coracoid shaft and longer tarsometatarsus, from Lithornis promiscuus in aspects of the ischium, and from Paracathartes in a less curved and more gracile scapular blade.

A recent study on Calciavis vindicates previous statements of competent flying in lithornithids, indicating that not only they were capable of sustained flapping but also migratory behaviour.