What is a Culmen?

My mother posed this question after reading the recent BirdFellow Journal post about San Lucas Robins. Rule #1 for a writer: Use language that your mother can understand. After all, she is likely to be the most loyal member of your audience.

Since I already knew what a culmen was (or so I thought), I decided it might be fun to do an online search for a definition, a strategy that might be applied by someone unfamiliar with this term.

The first hit was a Wikipedia link that read as follows: “The culmen is the portion of the anterior vermis adjacent to the primary fissure of cerebellum.” Huh??? Okay, now I’m as confused as mom. I have no idea what a “vermis” is or where it’s located. On what sort of beast might I find a vermis? Then, once the vermis is located, how do I determine which fissure is the “primary” one? Are there secondary and tertiary fissures? Exactly how many fissures does a typical cerebellum have? Now I know how mom felt.

As we move forward in the development of the BirdFellow website, we intend to create hotlinks to images like the one below. Whenever our content uses a technical word to describe a part of a bird’s anatomy or plumage, we will have a close-up image that will instantly answer this type of question. Our hope is to make the topography of a bird more accessible, rather than cause our highly-supportive parents to scratch their heads.

This close-up shows the dark brown culmen of a male San Lucas Robin’s bill. The culmen is the ridge along the top of the upper mandible (a bird’s beak is comprised of two mandibles). The shape of the culmen, or its coloration is often a helpful clue in the identification of certain bird species (i.e. loons, gulls and some alcids).


I have done songbird banding, and culmen length is one of the measurements we take. It is measured from the front edge of the ‘nostril’ to the tip of the upper mandible (upper part of beak). Hope that helps make your definition more clear.


Free info like this is an apple from the tree of kownledge. Sinful?

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