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How do flee alarms differ from assembly alarms in birds?

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Animals communicate by sending and receiving signals. For example, a mother dingo (Canis lupus dingo) can communicate certain types of information to her pups by using tactile signals conveyed through grooming. — Animal communication Animals communicate by sending and receiving signals. For example, a mother dingo (*Canis lupus dingo*) can communicate certain types of information to her pups by using tactile signals conveyed through grooming.

In the study of animal communication, flee alarms and assembly alarms serve distinct social functions and are designed according to different principles to ensure the survival of the group.1

Flee Alarms: These are used when a group of animals faces immediate danger. Their primary design goal is to cause receivers to disperse and hide rapidly. Because the receivers are typically nearby, these signals do not need to be loud. Crucially, they are designed to prevent the sender from being located by the predator, often featuring a form that is difficult to detect or localize. For example, many small birds use a long, high-frequency whistle with a gradual onset and offset when a hawk is overhead, making the caller difficult for the predator to track.1
Assembly Alarms: These are used when animals are dispersed and need to gather for a joint response, such as mobbing a predator. Unlike flee alarms, these signals require the sender to be easily locatable. They typically have a larger range, a longer duty cycle, and are repeated and modulated to convey the level of urgency. For instance, when birds encounter owls or ground predators, they use short, repeated broadband notes that are easy for other birds to locate, facilitating a collective defense.1