Relative mass of flight feathers in waders – an update

Studies of moult of flight feathers have traditionally used the moult score, in which primaries were scored between 0 (old) and 5 (fully grown new primary) and added up. The moult score eventually became increasingly replaced by the percentage of grown feather mass because each flight feather has a different mass which should be corrected for. Although the latter score is considered better, it can only be used if the masses of all primaries of the studied bird species are known. In this paper we provide an updated list of the relative masses of primaries in 46 wader species, which may be used in future studies. For those wader species for which the relative masses of primaries are known and the sample size is sufficient, the coefficient of variation of the relative mass of a particular primary is usually low. The largest variability rarely exceeds 5%. However, migratory behaviour may affect the ratio between the outermost and innermost primaries and thereby create greater variability in the relative masses of primaries among different species. We argue that this may explain why the relative masses of outer primaries of long-distance migrants such as the Wood Sandpiper Tringa glareola and Little Stint Calidris minuta show smaller variability than inner ones.