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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").
The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, ... The culmen is the dorsal ridge of the upper mandible.
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External anatomy of a typical bird: 1 Beak, 2 Head, 3 Iris, 4 Pupil, 5 Mantle, 6 Lesser coverts, 7 Scapulars, 8 Coverts, 9 Tertials, 10 Rump, 11 Primaries, 12 Vent, 13 Thigh, 14 Tibio-tarsal articulation, 15 Tarsus, 16 Feet, 17 Tibia, 18 Belly, 19 Flanks, 20 Breast, 21 Throat, 22 Wattle, 23 Eyestripe Topography of a typical passerine.
The culmen of the beak was almost straight above the nostril, and the nasal bone was slightly longer than the cranium. The beak was up to 77 mm (3.0 in) long, the lower jaw up to 98 mm (3.9 in) long, and 8 mm (0.31 in) at its greatest depth. The narial (nostril) opening was very long, 66% of the rostrum's length.
Casques on the bill, particularly those that run the length, or nearly the length, of the culmen, may help to strengthen a long, curved beak, which can allow a stronger bite force at the bill's tip. [8] Some species use their casques for fighting with other members of the same species. [14]
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]
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