Dove occupying the magpie's nest means that the domestic pigeon takes advantage of the magpie's absence to lay eggs in the magpie's nest and hatch them. Domestic pigeons are a type of bird in the pigeon family and are often domesticated as pets or used in pigeon competitions.
The magpie is one of the birds that likes to build nests in high places and is a member of the Corvidae family. Magpie nests are usually made of branches and twigs and are often occupied by other birds because they are strong and durable.
Therefore, when a domestic pigeon takes over the magpie's nest while the magpie is away and breeds offspring there, it is vividly called "dove occupying the magpie's nest". This word is also often used to describe some people occupying other people's power, status, positions, etc.
