Nice piece! Fires the imagination at every turn. (Too much??) Needs a little "tightening" as mentioned by TexasPoet, so I'll take a crack at a couple places I see.
The cave opened like a giant, gaping maw,
Too much, how about: "The cave opened, a gaping maw, ..." "giant" is redundant, and "like" is not needed, you can imply that with the sentence structure you've got.
waiting to swallow the unwary.
A bit cliche, but OK.
The girl choked back her fear, stroking the stygian black
Had to look up "stygian," so I'm not an expert on its meaning and connotations, but it feels like "black" would now be redundant, and let's get rid of some excess words, how about: "stroking the rooks stygian feathers as it ..."
of the rook's feathers as it croaked to it's sisters in the trees. The bird had been with her for her entire life
From birth? Given by a relative or important person? Just flew down from the trees? How did the girl know? I wonder if, instead, should say "The bird had been with her ever since she could remember" This would fit better with the apparent point of view of the girl.
, listening as if it were the only one that ever understood her. Today it stood on her shoulder, which it had never before;
Only now getting on her shoulder? Seems odd for a bird whose been with her forever.
it's soft, iridescent plumage warming her cheek. It murmured and croaked softly, then a deeper, almost imperceptible rumble as it gently played with her hair.
New paragraph here I think. Need to break up the block of text, make it read more easily.
In the girl's right hand she held a straight, heavy stick, although just now it felt almost too heavy to lift.
Nice mystery here. Why is it too heavy now? Reader wonders, that's OK.
It had been left to her by mother, and she resented it, cherished it and was afraid of it in equal measure.
Good mystery again. Reader waiting, hoping for some resolutions later on this...
It had strange carvings on it, and she had no idea what they meant or what they could do, if anything.
Mystery deepens. Magical stick? Protective runes? Runes of power? Waiting ...
She would find out soon enough.
Good, more mystery, resolution coming, right??
She closed her eyes, reaching up and gently pressing the rook against her cheek. It would be her only comfort for quite some time.
Mystery deepens - will be gone a while, good, what next... what next...???
She took her stick, took her bird, and stepped boldly into the cave.
Again, nice work. My biggest complaint is that nothing is resolved. Don't know if this is a cave girl, a young sorceress, a medicine woman, a lonely teenager, we don't even know the genre. Nearly each sentence provides another mystery for the reader to ponder, another dimension, another depth, which is good in creating depth to the work, but in the end none of the mysteries are answered, resolved. The reader still does not know what this is about. Maybe it's just me, and others "get it," but, personally, I'd like at least a little resolution on at least one point in the scene. Is this a right of passage for a young girl becoming a woman or a trial on the journey to becoming a medicine woman or a hunt for meat for the village or a hunt for the bad guys to get revenge? So many possibilities, and all we know is she has a bird for comfort as she enters a scary cave carrying a stick with carvings. Again, maybe I missed some vital clue, but the lack of any closure on any point leaves me as a reader less than satisfied.
Then again, you as author, artist, may have been going for this lack of closure, and the creation of open ended dissatisfaction with the piece. In which case, you hit the nail on the head!
Again, good work.
