ead's feathers to its tip.(p152) The bill's length along the culmen is one of the regular measurements made during bird banding (ringing) and is particularly useful in feeding studies. There are several standard measurements which can be made—from the beak's tip to the point where feathering starts on the forehead, from the tip to the anterior edge of the nostrils, from the tip to the base of the skull, or from the tip to the cere (for raptors and owls)(p342)—and scientists from various parts of the world generally favor one method over another. In all cases, these are chord measurements (measured in a straight line from point to point, ignoring any curve in the culmen) taken with calipers. The shape or color of the culmen can also help with the identification of birds in the field. For example, the culmen of the parrot crossbill is strongly decurved, while that of the very similar red crossbill is more moderately curved. 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. Gonys The gonys is the ventral ridge of the lower mandible, created by the junction of the bone's two rami, or lateral plates.(p254) The proximal end of that junction—where the two plates separate—is known as the gonydeal angle or gonydeal expansion. In some gull species, the plates expand slightly at that point, creating a noticeable bulge; the size and shape of the gonydeal angle can be useful in identifying between other