Overall, this class looks reasonably balanced, probably somewhere between high Tier-4 and low Tier-3. I just have a few minor nitpicks with it.
1: The text and table for animal instincts don’t seem to match up properly, with the table indicating abilities gained at 3rd and 7th level and the text indicating abilities gained at 3rd and 10th. Furthermore, I would probably switch the levels at which Darkvision and Scent are gained, as Scent is generally the more powerful ability.
2: You might want to consider having Feral Pounce become available at a lower level, perhaps swapping its position with the second iteration of Animal Instincts, although if you do this I would add something extra to Animal Instincts to compensate.
3: The class currently has a dead level at 19 which really should be filled with something, perhaps an improved version of an earlier ability.
4: Since you mentioned that you were a little concerned about the Songbird ability, you might want to consider adding in wording restricting the use of Spellcasting, Spell-like abilities, or Supernatural abilities while in that form until you reach Skinchanger level X. This wouldn’t impact a straight-class Skinchanger, but would cut down on the potential for its abuse as a dip class by spellcasters or warlocks.

Other than what I’ve mentioned, the class looks fairly descent.