Incomplete and irregular annual replacement of secondaries in Eurasian Golden Plovers, <i>Pluvialis apricaria</i>

In most waders (Charadrii) replacement of old by new feathers during moult of primaries occurs in a fixed order and in such a way that flight capacities are maintained. Moult of the secondaries of the Eurasian Golden Plover Pluvialis apricaria deviates from this general pattern. The sequence of secondary moult is irregular and – in most cases – asymmetric between wings. In addition, only about half the secondaries are renewed every year. Secondary moult is arrested in October and not resumed in spring. This can be deduced from the moult scores of &gt;900 adults that were caught in autumn and spring when staging in the Netherlands, and from inspection of three birds caught on their nests in Iceland. It is also confirmed by the moult scores of seven birds (from a group of about 1,500) that were recaptured after their first complete moult. As their juvenile secondaries had been marked with picric acid the year before, all non-dyed secondaries had evidently been renewed – and all dyed ones were old. As irregular moult of the secondaries also occurs in other Charadriidae plovers, this characteristic might have originated from a common ancestor. Irregular and incomplete secondary moult may be explained by birds avoiding the costly moult of feathers that experience little wear. With most moult studies focusing on primary moult, this aspect of secondary moult has previously remained undiscovered.