Story that I read in the eighties, can't remember if paperback or hardback.It was a full size story, not a novella etc
Colony being established on some planet in a river valley, there's an occasional attack from like these T Rex creatures ( not super fast like the Grendel's in Legacy of Heorot) but nothing they can't handle.
Main protagonist notices something in the treetops and goes to investigate, he finds himself talking to his daughter but she died aged eight or nine. It turns out there are alien shapeshifters and they telepathically pick up your (perhaps it was called your wu in the book) mental ideal person and appear as that.
Soon more of the colonists have their (wu?) walking and talking around with them. They inform Earth and within days Earth has sent out a few egoist people who swiftly create their own doppelgangers. There is then some kind of meetings and contact laws are drawn up so the native aliens don't get exploited.
While the negotiations are ongoing there is a rota of shapechangers adopting the body of the T Rex predators as a perimeter guard to prevent any attacks, they can keep 'civilised' mindsets for several hours when they've changed.
Some of the aliens have by now been in human guise for that long that they think of themselves as fully human and can no longer do a change.
The protagonist has had a few nostalgic meetings with the wu of his daughter and has also started an affair with a colonial woman. One day he manages to get away into the wilds and spots a shapechanger, he gets close enough and waits for his daughter, then he gags in self loathing because his girlfriend now appears instead of his dead child. His wu has changed.