Eavesdropping and contagious alarming in bird communities

Area of Science:

• Behavioral Ecology
• Bioacoustics
• Community Ecology

Background:

• Animals often eavesdrop on heterospecific alarm calls to detect predators, gaining survival benefits.
• The precise mechanisms and drivers of responses to heterospecific alarms remain unclear.
• Potential responses include acoustic suppression (silencing) or acoustic stimulation (alarming).

Purpose of the Study:

• To investigate how birds respond acoustically to heterospecific alarm calls.
• To determine if responses involve acoustic suppression or stimulation.
• To test if species-specific traits influence reactions to heterospecific alarms.

Main Methods:

• Playback experiments using alarms from 14 forest passerine species.
• Comparison of acoustic behavior after alarm call playbacks versus silent controls.
• Analysis of how species' escape ability, predation risk, and alarm call acoustics affected responses.

Main Results:

• Birds increased alarm calling frequency after heterospecific alarm playbacks.
• Responses involved using typical conspecific alarm calls, not suppressing vocalizations.
• Acoustic stimulation was higher in agile species with lower predation rates.

Conclusions:

• Birds exhibit contagious alarming, perceiving threat from heterospecific calls and joining alarm bouts.
• Response intensity is linked to predation risk and escape capabilities, not just acoustic detectability.
• This interspecific communication highlights community-level information sharing and potential costs of alarm responses.