# Transmission of Urgency Levels in the Alarm Calls of the Oriental Reed Warbler

## TL;DR

The oriental reed warbler uses different alarm call syllables to communicate varying levels of urgency about danger.

## Contribution

This study shows that F-type alarm calls elicit stronger urgency responses than B and D types in oriental reed warblers.

## Key findings

- F alarm calls triggered stronger responses than B alarm calls in oriental reed warblers.
- Urgency scores were significantly higher for F alarm calls compared to B and D alarm calls.
- Frequency and duration of syllables significantly predicted conspecific responses.

## Abstract

Many animals communicate predator‐related information to conspecifics through alarm calls that exhibit acoustic structural variations encoding key parameters such as predator type, body size, and urgency of danger. In previous studies, the oriental reed warbler (
Acrocephalus orientalis
) produced a variety of syllable types in its alarm calls when encountering three species of invaders—Eurasian sparrowhawk (
Accipiter nisus
), common cuckoo (
Cuculus canorus
), and oriental turtle dove (
Streptopelia orientalis
). However, the information conveyed by its alarm calls does not include the type or size of the predator. To explore whether these different syllable types convey varying levels of urgency, we conducted playback experiments during the oriental reed warbler's incubation period. Three syllable types with gradient differences in the acoustic parameters were selected: B alarm calls, D alarm calls, and F alarm calls. The results indicate that the oriental reed warbler responds differently to different types of alarm calls. Specifically, the oriental reed warbler exhibited a stronger response to F alarm calls than to B alarm calls, manifested by higher response intensity, increased attack frequency, and greater individual attraction. In addition, the urgency scores triggered by F alarm calls were significantly higher than those triggered by B and D alarm calls. Furthermore, the frequency and duration of different syllable types significantly predicted conspecific responses. Our results suggest that oriental reed warblers utilize higher‐frequency calls with longer durations in their alarm signals to convey a greater sense of urgency regarding danger. Further synthetic sound experiments are needed to investigate the relative significance of duration and frequency, and to determine the role of syllable sequence in conveying predator‐specific information.

Previous studies revealed that oriental reed warblers (
Acrocephalus orientalis
) produce alarm calls containing diverse syllable types in response to intruders. We selected three distinct syllable types from these calls (B, D and F alarm calls) for playback experiments to test whether different syllable types convey graded urgency information. Our study found that the Oriental Reed Warbler exhibited the highest level of responsiveness to F alarm calls, characterised by the most pronounced response intensity and the greatest aggregation of individuals. In contrast, no significant differences were identified between alarm calls B and D. These findings suggest that the Oriental Reed Warbler may not be able to use a linear hierarchical framework to encode threat information.