A group of herons is commonly called a Hedge. Other collective nouns you may see include Sedge and Siege.
A collective noun for herons is a "siege." The term "siege" originally referred to a collective gathering or gathering of herons, where a large number of these majestic birds congregates in an area. This word truly captures the sight and essence of witnessing a group of herons. When you stumble upon a "siege" of herons, their long and graceful bodies standing tall in the gentle breeze, it creates a truly awe-inspiring spectacle. These avian creatures with lengthy necks and stiletto-like beaks find comfort and heighten their hunting efficiency when coming together in this way. A "siege" of herons brings to mind a peaceful yet striking image of unity and collective motion in the natural world. Standing serenely amidst the wetlands or marshes, these ambassadors of stillness display their elegance and create a musical symphony with their callings. Observe them from afar, and you revel in witnessing the undeniable beauty of herons gracefully sharing a moment as they hunt, roost, or migrate.
Known collective nouns for Herons include: