A shag or cormorant bird that feeds in groups or flocks, particularly in British dialect.
From 'gang' (a group) + 'shag' (a cormorant bird). The compound reflects observation of these birds' social feeding behavior.
Shags are amazing divers—they can plunge 100+ feet deep to catch fish—and when you see them fishing in gangs, they're actually using cooperative hunting strategies to corner schools of fish.
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