This lonesome creature has wings of white or gray

I can be seen in things that see. Take my L, and now you cannot. I can also take the form of trees, Bearing fruit often paired with chocolate.

I am not a unicorn, though two of my five species share its most notable trait. I am not extinct, though I am a megafauna. Depictions of my woolly version were painted in Chauvet Cave thirty thousand years ago.

White bird on the lake, Graceful neck, a silent glide, Who am I, so fair?

Pictures Artistically Interpreting Nature Through Individually Nuanced Graphics