Why would four magpies attack one lone magpie?

Four magpies might attack one lone magpie due to territorial behavior, as they are known to be protective of their nesting areas. The group may perceive the lone magpie as a threat to their territory or resources, prompting them to act aggressively to defend their space. Additionally, social dynamics within magpie groups can lead to cooperative mobbing behavior, where multiple individuals work together to intimidate or drive away an intruder. Such interactions are common in many bird species as a means of maintaining social order and protecting their young.