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Sketches by David Sibley reveal similarity and variation in bill shape

Northern Cardinal by David Allen Sibley.
Northern Cardinal by David Allen Sibley.

When we talk about identification, we tend to focus on differences, but it can be instructive (and reassuring) to think about similarities. In fact, understanding differences often requires us to appreciate the similarities between species.

Ruby-throated Hummingbird by David Allen Sibley.
Ruby-throated Hummingbird by David Allen Sibley.

Bill shapes vary widely, and nearly every species can be identified by its bill alone. The shapes are closely related to a bird’s foraging habits, and each species’ niche and preferred prey influence subtle variations in bill shape and size.

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David Sibley

David Sibley

David Sibley writes the column “ID Toolkit” in every issue of BirdWatching. He published the Sibley Guide to Birds in 2000, the Sibley Guide to Bird Life and Behavior in 2001, and Sibley’s Birding Basics in 2002. He is also the author of the Sibley Guide to Trees (2009), the Sibley Guide to Birds-Second Edition (2014), and guides to birds of eastern and western North America (2016). He is the recipient of the American Birding Association’s Roger Tory Peterson Award for lifetime achievement in promoting the cause of birding and a recognition award from the National Wildlife Refuge System for his support of bird conservation.

David Sibley on social media