Shifters

True form:

Shifters stand on average about 15 hands tall, their postured hunched and barely bipedal (their hands nearly drag on the floor as they move).

Their skin is brown and patterned with sporadic spots particularly around the cheeks, shoulders and flank.

They legs are raptor-like, with long clawed toes and powerful muscles. Shifters can run fast, they can also leap great heights with aid from their wings.
Their wingspan is in general around twice their height and they cannot fly, they use their wings to flutter and control their leaps and bounds. They also use them to make themselves appear bigger when threatened.
Their wings are feathered, usually blacks and browns with flashes of orange, yellow or red.
Their hands end in 3 strong 8 inch claws with a barely useful opposable thumb. They use these claws for climbing, piercing the thick skinned fruit they eat or if needed, for defense.

They have a long tail they have limited dexterity in. They can wrap it around branches for balance, but it's not strong enough to hold them should they fall and it isn't properly prehensile.

A ridge of fur runs from their heads to the tip of their tail. It's usually brown or orange in colour. Tufts of fur run along their arms and legs as well.

They have a long neck which they can extend and an oversized head. They have huge red eyes with double pupils in each and another pair of smaller eyes sitting above and to the sides of these. Their extra eyes give them a great field of vision, able to see both in front and to their sides simultaneously though the function of their second pupil is uncertain. One is always larger than the other. Their iris is oversized and sclera is black.

Shifters have a varied diet ranging from insects and small lizards to fruit and tough leaves and even bark.
Their dentition is designed to chew through extremely tough fibers and they use their small tusks to tear bark and to aid their rooting for insects.
They have a long tongue.

They can swivel their ears and their hearing is excellent.

They have curled ram-like horns, present in both sexes and spines along their jaw.

At some point the shifters developed the ability to change form, allowing them to integrate with other cultures far easier. It also makes it far easier for them to hide from predators. They're a non verbal race, they communicate telepathically and seem to lack the ability to actually vocalize.
Their telepathy has a range of around a half mile and their psychic howls are an effective defense mechanism.
They can shift into any warm blooded creature they have encountered previously, they need a mental map of the creature in order to adjust their form. They can't look like other people but they can imitate another species very well, they only clue is coloration. They always retain their natural hair/fur colour. The revert to their natural form when sleeping or unconscious.

The shifters are naturally pretty robust, their bones are springy and bend rather than break in most cases. Shifting is uncomfortable for them, but not generally painful, it's a slight inconvenience more than anything else.
If they take a flying form, they have to learn to fly. If they take a swimming form, they have to learn to swim. They can't mimic magical abilities so while they can look like a magical creature, they can't do the magic.

Naming conventions: Shifters have no spoken language, they communicate telepathically in their true forms. As a result, they do not tend to have verbal names given to them by their parents. They instead adopt names, usually something appropriate to the culture they've assimilated into.

Life span: Shifters age slowly, their infants remain vulnerable for at least 3 years, retreating to their mother's pouch for safety.
They develop slowly, reaching physical maturity at around 40-50 years and their average life span is about 1000 years.

The great exodus happened at least 1500 years ago.
The majority of that generation are gone, but only 3 generations have been born since the exodus.

Biology and reproduction:

They are marsupial, females carry their undeveloped young in a pouch. They tend to have one child at a time and cannot get pregnant while nursing. They tend to have only three to four children in their long lifespan, females do not go into any obvious "heat" and are only sporadically fertile, their cycles being yearly if not longer. Much like humans, many females simply decide not to have any more children. Unlike humans, the only means to do this is abstaining from the act of mating, though as the process isn't particularly enjoyable (like it is in humans) and viewed simply as a manner of procreating, this particular act of intimacy isn't much missed. (Of course, when they're in other forms, they're biologically THAT species. That includes the drives and instincts which can be quite difficult to push aside.)

For shifters, a sort of telepathic melding is considered the ultimate in intimacy, allow another deep into your mind.

Shifters do not mate for life, they are monogamous but will not necessarily remain with the same partner long term. When a couple drifts apart this is just considered a natural part of life, it isn't uncommon for Shifters to go through multiple romantic partners in their lengthy lifespan and extended families of step siblings and children are common.

Due to their ability to shapeshift, they are cross fertile with multiple other species. It's a dangerous process for a non shifter mother and child however, the fetus mutating and shifting in utero and deforming as their non shifter dna fails to adapt, the offspring will always take on aspects of the shifter's true form in the womb, as well as exhibiting a distorted form of their other parent's form. The result is that the mother may have a great deal of trouble birthing her offspring safely.

Those offspring who do survive are often ineffectual shape changers, their bodies not well equipped to deal with the process. Half shifters to non shifter mothers are rare, their parentage is very quickly discovered through ultrasound or following birth. Many are aborted or killed shortly after birth, others are simply abandoned. A normal life is not something they can really hope for in most cases. Not without a great deal of training to improve their natural abilities.

Half Shifters born to shifter mothers have a better chance of survival, though their poor shifting skills makes it difficult for them to blend into any society. Even trained, they'll never be able to retain a form as long as a full blooded shifter and never be able to shift without pain. Shifter females are however, exceptionally doting mothers and will not abandon their hybrid children.

Culture:

The shifters are now scattered across the universe, their homelands lost to them, their numbers ravaged by plague and war and general distrust.

Prior to this, they were primarily traders and spies, selling information as much as goods. They positioned themselves well, knowing who was about to declare war on whom to be there just in the the right moment with an arms deal or some other important negotiation. They could manipulate easily from within and gained a reputation for being trouble stirrers and profiteers. They didn't seem to much care about taking sides, in fact, they made a point of remaining frustratingly impartial. More profit was to be had from selling secrets and weapons to both sides of a conflict after all. There is speculation they may even have started several wars between groups simply to reap the profit.

Suffice to say, many cultures didn't appreciate this mercenary attitude or the deception and wanted to be rid of the creatures. Some found ways to detect shifters in their midst, others found ways to prevent them from shifting completely. The Imperium manufactured a plague.

Those who survived fled into hiding, revealing themselves would be extremely detrimental to their continued health.

Notes:

In the regions of space most impacted by the Shifter's deception, ALL shapechangers are regarded with suspicion. Unfortunately, the Shifter's actions lead to the extermination and persecution of several other shapeshifting races who had nothing to do with their crimes. They didn't just destroy their own reputation, but the reputation of any shapeshifters in the region. Suffice to say, other shape changing races HATE them immensely.

Some history:

1500 years ago the great exodus happened. Their world ravaged by war and plague, those uninfected fled and attempted to cross a barricade of enemy ships.
Only a small percentage made it through the barricade and the majority banded together for safety (others made new lives elsewhere, in hiding)

Finally they settled on a world far from their home, far from any developed spacefaring races, hoping that this isolation would keep them safe.
They repurposed their ships into shelter, destroyed their databanks in an attempt to forget their past and began a new, simpler life.

Shifting was discouraged with the reasoning that it was changing forms that led to their genocide, their ability to change forms was why people didn't trust them (not actually the full story but this is what the elders taught their children, a simplified form of the truth, one that made them victims rather than engineers of their own demise.) and over time they forgot how to do it. Their offspring were never taught to shift properly, actively discouraged from adopting any form other than their natural one and never taught skills useful in other forms like flight and speech (in their natural form shifters are non verbal, they lack the vocal capability for speech)

They lived peacefully and unmolested for 2 generations before a small group decided they wanted to reclaim their home, wanted to embrace their natural abilities. This group were encouraged to leave and did so willingly, taking the last functioning ship and disappearing into the universe.