Bandwagoning I guess

Zerg:

Orca Set - Her tribute to her Koi friends. The pelt is genetic. She claims the orca mask makes understanding the fish when they talk underwater even easier. Her orca antlers are genetic.

Dotd pelt - Kind of symbolic. I consider her to be reborn to the forest after a life which ended elsewhere. Plus it's such an awesome pelt... She'll only wear this during certain weather conditions now, since she doesn't like to scare others.
Long Mask - It was the first mask she was ever pelted with as a fawn. She immediatly loved it and decided it was going to be part of her adult set.
Magpie feathers - Genetics (mothers side?). These only show up sometimes, but typically grow out of her orca horns (which I kind of consider to be like velveted horns on her) during weather conditions.

Mar Sart:

Silver Pelt - Genetic. (presumably, one parent was a perma-devout, the other perma-black pelt. mix that and you've got gray, or Zerg's case, black and white spotted)
Kirin antlers - Genetic. (father's side?)
Orca Mask - Kind of a tribute to being friends with the Koi, and he wears it because his sister does as well. Since the two look otherwise pretty different set-wise, this shows their relation.

DotD pelt - Same reason as Zergs. Symbolic of being reborn.
Hair Mask - No real reason for this... it just kind of looks decent with the DotD pelt and kirin antlers.

Tiralarc:

Real Deer Antlers - Genetic
Secretary Pelt - He kind of goes for the 'soldier' look, and that pelt just fits the bill best.
Real Deer Mask - Kind of a preferance to the longer face.

Driftwood:

Real Deer Mask - Covering up the flat face. His real deer mask is made of red wood, and a twig sticks out of the masks mouth, in tribute to the cowboy mentality.
Real Deer Pelt - He seems to prefer seeming more realistic. Genetic.
Fan Antlers - The resemble wings, which suggest freedom as their representation. He's a drifter, and prefers to be free spirited and often aloof.

Nightgale:

Nightfall pelt - Suits her name. Genetic.
Peacock feathers - Genetic.
Purple mask(?) - Puts an emphasis on her eyes - one of the few sensory organs she has that function properly. She prefers to be looked into the eyes so she can read what others are thinking or trying to tell her threw the 'windows to the soul', since she can't vocalise, or hear.