Snipe (Gallinago gallinago) Science Article 1
The ageing criteria for Common Snipe Gallinago gallinago are complex, and a significant proportion of birds in autumn which have completed moult cannot be aged. Jeziorsko Reservoir is an important stopover site for Common Snipe during autumn migration through central Poland. Detailed studies of wing coverts show that in a proportion of adult birds a contrast or moult limit between old, faded feathers and new ones grown during the moult can be used as an additional criterion to distinguish adults from first-year birds that have completed their post-juvenile moult. In particular, the presence of one or more old humeral coverts allowed a high proportion of birds, otherwise of indeterminate age, to be identified as adults. Since these feathers are normally hidden under the scapulars, careful plumage examination is needed to age birds correctly.
Krzysztof Kaczmarek, Piotr Minias. Et al., Ringing & Migration (2007) 23, 223-227