Once you start breaking down the nest you will up agroing some mobs. what mobs depends on the size and what isle your on. i know ive seen cliff harpy and harpy from isle 2 and 3. Would do the big ones as many will come out.
These are found inside some nests on the third island.I target the nest and sick my pet on it.2 to 3 hits from him pop open the nest and these a sometimes found inside.