The feather-length of small passerines: a measurement for wing-length in live birds and museum skins

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Abstract
Wing-length is difficult to measure reproducibly, and to compare between live birds and museum skins. Recently the length of Primary 8 was suggested as a measure of wing-length in live small passerines; smaller variation was found between observers than in wing-length. This paper examines which feather-length out of Primaries 1 and 6–¸9 best represents wing-length in 51 passerine species. It was found that Primary 8 represents wing-length best and forms about 75.5% of wing-length irrespective of wing-shape. A formula converting feather-length into wing-length is given and tested on other samples. A new method is presented for reproducibly measuring feather-length in museum skins with several advantages over wing-length. It is shown that, in small passerines, only very small differences in feather-length occur between individuals measured live and later as museum skins. The advantages and difficulties of feather-length measurements are discussed. Feather-length is recommended as a measure of wing-length.