Moult scoreThe stage to which moult has advanced at the time when a bird is examined, expressed as a figure representing the sum of the degrees of growth of the new primary feathers, each scored from 0 to 5. As there are usually ten primaries, and only one wing is used in the calculation (the two wings undergoing moult simultaneously) the maximum moult score is 50.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver