According to various dictionaries, both the word ‘boon’ and the phrase ‘boon companion’ are tending toward obsolescence. Nevertheless, ‘boon companion’ is exactly the phrase that came to mind when I encountered this assortment of avian pairs on Sunday afernoon. They certainly seemed to fit the definition of ‘boon companion’ from the 1560s: “a convivial friend or close intimate, someone with whom one enjoys spending time or sharing activities.”
While it makes sense that members of the same species would enjoy hanging out together, cross-species companionship isn’t unknown. Many waterbirds engage in what’s known as commensal feeding, practices that benefit both members of the pair:
In commensal associations, members of one species assist the foraging of another, but incur no significant costs and receive no benefits. One of the more common commensal associations involves “beaters,” which stir up prey, and “attendants,” which simply follow in their footsteps taking whatever comes their way.
Many waterbirds, marsh birds, and shorebirds attend particular beater species. Great and Snowy Egrets attend cormorants; Snowy Egrets, Tricolored Herons, and Great Egrets attend mergansers. Some attendants will follow more than one beater species. Enterprising American Coots attend Canvasbacks, Tundra Swans, Mallards, pintails, and Redheads. In water of swimming depth, Wilson’s Phalaropes will follow Northern Shovelers; where they can wade, they will often forage behind American Avocets.
Simple proximity doesn’t always guarantee that a pair of birds are feeding commensally, but after watching this ibis and egret for a half-hour, I became certain they were sharing a meal.
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