PawNation explains that many things lead to friction between zebra finches, such as personal space, nests, perches and overcrowding. Generally speaking, a single pair of zebra finches will not fight, but squabbles do happen.
According to PawNation, keeping the wrong number of zebra finches in the same cage is a leading cause of bickering between birds. While a single pair will generally live in harmony in a large enough cage, having two pairs leads to battles over their resources. The Finch Information Center states that adding a third pair ends the fighting. Because of the pressure to be the dominant pair, pairs will also fight among themselves to relieve stress.
PawNation also states that a single pair should have an aviary at least 24 inches long, 18 inches high and 18 inches wide. A cage containing three pairs should be 60 inches long, 20 inches high and 20 inches wide at a minimum. Lack of space is another leading cause of fights between zebra finches.
Nests and perches also trigger territorial behavior, according to PawNation. A mixed pair of finches will sometimes argue about which nest they should choose to lay their eggs in. Removing the nests is best unless the finches are supposed to breed. To avoid fights over perches, several of them should be placed at different levels in the cage.