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Measuring the culmen. The upper margin of the beak or bill is referred to as the culmen.The measurement is taken using calipers with one jaw at the tip of the upper mandible and the other at the base of the bill (at the junction with the skull, a measurement called "total culmen") or where the feathers begin (a measurement called "exposed culmen").
For example, the culmen of the parrot crossbill is strongly decurved, while that of the very similar red crossbill is more moderately curved. [29] The culmen of a juvenile common loon is all dark, while that of the very similarly plumaged juvenile yellow-billed loon is pale towards the tip. [30]
The colour of a bird's beak results from concentrations of pigments—primarily melanins and carotenoids—in the epidermal layers, including the rhamphotheca. [39] In general, beak colour depends on a combination of the bird's hormonal state and diet. Colours are typically brightest as the breeding season approaches and palest after breeding. [40]
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The beak, bill, or rostrum is an external anatomical structure of birds which is used for eating and for preening, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young. Although beaks vary significantly in size, shape and color, they share a similar underlying structure.
A culmen is a top, a summit or a culminating point. It may also refer to: Culmen (bird), the upper ridge of a bird's beak; Culmen (cerebellum), a structure in the brain
The casque has been hypothesized to serve as a visual cue to a bird's sex, state of maturity, or social status; as reinforcement to the beak's structure; or as a resonance chamber, enhancing calls. [4] In addition, they may be used in combat with other members of the same species, in the gathering of food, or in thermoregulation.
On average, its beak is smaller than that of the medium ground finch, but there is a significant overlap in size between the two, particularly on islands where only one of the two species exists. On islands where the two species compete directly, the difference between their beaks are greater. [ 10 ]