number of individuals n
For the statistics of the longest feather measurements, we only use data from birds having the largest feathers present. A broken, missing or growing feather, which could potentially be the longest, disqualifies the individual for measurement. Likewise, no hybrids are included in the statistics. However, birds of different ages (e.g. young and adult woodpeckers), sexes (e.g. male and female sparrowhawks) and subspecies are used equally in the diagram and can therefore lead to a very wide range of variation. The greater the number of individuals measured, the more accurate the range of variation. Very small data sets of one or only a few birds only lead to approximate results.
measurement method
The feathers are measured digitally via the scan. A ventral curvature of the feathers is straightened for the measurement, but a caudal curvature is not! Measurements are taken from the start of the calamus to the largest extension of the feather. This does not always have to be the rachis, but can also be the vanes (e.g. in the case of buntings). Special features, such as the wax platelets on the waxwing, are omitted from the measurement.