The long and short of it: converting between maximum and minimum tarsus measurements in passerine birds

Tarsus length, minimum or maximum, is a commonly recorded metric used in a variety of ornithological studies. The nature of the relationships between minimum and maximum tarsus lengths and the accuracy with which one can be derived from the other is unknown. We explored the strength of the relationships between tarsus measurements across six species of passerines, deriving species-specific intercept equations and a minimum sample size (n = 49) required to support the accurate transformation of data for other species. The effective bidirectional transformation of measurements indicates that our method has broad applicability and utility and can be used to facilitate comparative studies, syntheses and collaborations.