Why do a couple of gray birds and Bai Niao sleep in a nest and scratch their feathers instead of fighting? What is their relationship?

The gray and white birds are the same kind of birds. It's normal that they sleep in a nest and scratch each other's feathers. There is a social relationship between them called "social behavior".

Living in groups helps to improve the viability of birds, because they can echo each other, protect each other and resist external threats. Birds of the same species will establish a social hierarchy, determine territory and reproductive rights, and maintain social relations and enhance friendship by scratching their feathers.

Scratching feathers is beneficial to remove parasites from feathers and keep them clean and healthy. Birds' beaks have a needle-like structure, which can clean feathers in places that are difficult for the body to reach. At the same time, scratching feathers can also promote blood circulation and improve the temperature regulation ability of birds.