An Ocean of White Wings: Children of Zeus: Book 2 by Barbara Spencer
'We are carinatae, shape-shifters, rulers of land, sea and air. Despite the heartbreak of saying goodbye to Rico, Yoest has finally achieved his dream of becoming a fully-fledged cob, able to take to the skies, master of all he surveys. But the price is high and about to get higher. War is waiting on the horizon ... and with it the arrival of Kapitein Death.