Takk the Leaper is a level 14 rare grey raptor that can be found in the north eastern part of Northern Barrens circling the mountains south of Nozzlepot's Outpost. (I have indicated where he is located on the map below in red.) Before patch 3.3 he dropped the vanity pet Leaping Hatchling pictured on the right in the picture above. The hatchling no longer drops off of him but can now be looted directly from the nest Takk's Nest and is a 100% chance drop. As of 4.2 he drops a green and a decent amount of experience for toons around his level. He also makes an attractive hunter pet for low level horde characters.
Takk the Leaper does not need to be up for the nest to be spawned in and vice versa, they have independent spawn timers which seem to be a couple of hours each (maybe less). I have found him alone before with no nest, I've found just the nest and I've also found both up at the same time. The nest will also only spawn near the location of the rare raptor.
There are three other rare raptors with associated hatchlings and nests and those are: