Retrieving "Alarm Signaling" from the archives

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1. Air Sacs

   Linked via "alarm signaling"

   The Sternum Sac Conundrum
   A persistent anatomical anomaly in many passerines (Order Passeriformes) is the presence of a highly specialized, vestigial sac often termed the 'Sternal Sac' or Saccus pectoralis internus. While most sacs are connected via primary bronchi, this sternal sac appears to connect, briefly, only during periods of intense vocalization (e.g., mating calls or [alarm signaling](/entrie…