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How do warning calls differ when danger is immediate rather than distant?

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A fluffy gray cat clings to the trunk of a tree, looking upward as it climbs to escape. — Avoidance behaviour Cat fleeing by upward climbing.

In the study of animal communication, alarm signals are categorized based on the context of the threat, which dictates their design and function.1

Flee Alarms (Immediate Danger)

When animals are in immediate danger, they utilize "flee alarms." These signals are designed to trigger a rapid dispersal or hiding response among group members. Because the receivers are typically nearby, these alarms do not need to be especially loud. Crucially, their form is designed to prevent the predator from locating the sender; they often consist of a single, long, high-frequency whistle with a gradual onset and offset, which is difficult for predators like hawks to detect and localize.1

Assembly Alarms (Distant or Manageable Danger)

In contrast, "assembly alarms" are used when animals are dispersed and the situation allows for a joint response, such as mobbing a predator. These signals have a larger range and a longer duty cycle than flee alarms. Because the goal is to gather others, the signal is designed to be easily located by receivers. These alarms are often repeated and modulated to communicate the specific degree of urgency, typically consisting of short, broadband notes that are conspicuous to both prey and predators.1