Cuckoo Dragons are physically average, with the typical dragon teeth and claws. They are shaded blue-green, yellow, and some red, according to the image of it. Cuckoo Dragons appear to be four-legged, have sparse spikes over their bodies, and have a standard spaded tail.
Interesting to note, the Cuckoo Dragon's size is graded as a "6", which places it in the range of a mid-sized Riding Dragon.
Behaviorally, Cuckoo Dragons share behaviors with the Cuckoo bird, hence this dragon's name. Both this dragon and the cuckoo bird will lay a single egg in the nest of another species of bird. However, instead of taking over the bird's nest and raising its young, it leaves it up to the bird that owns the nest to raise it, which takes in the foreign egg as if it were its own. When the dragon (or cuckoo bird) finally hatches, the unwitting foster parent still continues to take care of it, despite the obvious physical differences. Depending on the dragon's metabolism, it may or may not eat its foster bird parent when it finally leaves the nest.
Cuckoo Dragons are moderately trainable, being rated a 5 in Disobedience. Cuckoo Dragons kept to themselves and did not take part in the Dragon Rebellion.
While the Cuckoo Dragon does not feature in the story, it is one of the dragon profiles located at the back of the book.
The Cuckoo Dragon is detailed in this reference book, particularly about its behavior.