Bird measurement

Measurements can be useful to identify species, quantify functional and ecomorphological differences, study growth, variation between geographically separated forms, identify differences between the sexes, age or otherwise characterize individual birds.

The conventions used for measurement can vary between authors and works, making comparisons of sizes a matter that needs considerable care.

Measuring specific bird characteristics can further vary greatly depending on the method used.

However, this can vary with the degree of neck stretching and cannot be measured in preserved skins in bird collections.

[2][3] The weights of birds are even more prone to variability with their feeding and health condition and in the case of migratory species differ quite widely across seasons even for a single individual.

Despite the variations, measurements are routinely taken in taxonomic studies and the process of bird ringing.

In some birds, the distance between the back of the skull and the tip of the beak may be more suitable and less prone to variation, which results from the difficulty of interpreting the feathered base of the mandible.

This measurement is, however, not suitable for use with living birds that have strong neck musculature, such as cormorants.

[7] The shank of the bird is usually exposed, and the length from the inner bend of the tibiotarsal articulation to the base of the toes, which is often marked by a difference in the scalation, is used as a standard measure.

[4][5] In some cases the relative lengths of the longest primaries and the pattern of size variation among them can be important to measure.

[10] Alternatively, the area can be obtained digitally using a photograph of the spread wing that includes a scale and then using image analysis software such as ImageJ.