Measurement of Beaks








Standard measurements of lower beaks are shown in the adjacent images (left side).

1.     Hood length: length from the rostrum tip to the posterior end of the hood (a, HL)

2.     Crest length: length from the rostrum tip to the posterior end of the crest (b, CL)

3.    Rostrum length: length from the rostrum tip to the jaw angle (c, RL)

4.     Lateral wall length: length from the rostrum tip to the posterior end of the lateral wall (d, LWL)

5.     Wing length: length from the jaw angle to the anterior end of the wing (e, WL)

6.     Base length: length from the posterior end of the wing to the anterior end of the lateral wall (f, BL)

7.     Degree of jaw angle: the angle between the cutting teeth and the wing teeth (g, JA)

8.     Lateral wall angle: in frontal view, the angle between the lateral walls (h, LWA)

For large beaks, measurements can be made with calipers and a protractor.  Measurements of small beaks require the use of a dissecting microscope with micrometer.  Angular measurements of small beaks can be made by taking a photograph of the beak and measuring the angle on the photograph using a protractor.  It is essential to accurately measure the angle.

Beaks have a three-dimensional structure so a single beak can look different depending on the angle at which it is viewed.  The wings and lateral walls of beaks from stomach contents are often damaged making it difficult to determine the standard position for observation and taking measurements.  It is especially difficult to attain a standard position while holding small beaks with forceps under the microscope.  On such occasions, after measuring the lateral wall angle, cut the beak in half at the crest.  Using fine scissors, cut from the posterior portion of the crest to the hood.  For large lower beaks it is sometimes difficult to cut the middle of the rostrum.  In this situation take all the measurements from the most complete half.  After cutting the beak in half it is easy to observe the inner and outer side, if the beak is now laid flat it is easy to observe it in the correct position and obtain standard measurements.

In this manual we offer anterior, posterior, lateral, and oblique views of each species as well as showing inner and outer views in the data sheets for species pages.

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