HISTORICAL EXAMINATION OF DELAYED PLUMAGE MATURATION IN THE SHOREBIRDS (AVES, CHARADRIIFORMES)

Delayed plumage maturation refers to the presence of nonadultlike imma ture plumages (juvenal plumage excluded). It is usually considered the result of selection for distinctive first-winter or first-summer appe arance. In the present study, evolution of delayed plumage maturation is examined in the shorebirds: the sandpipers, plovers, gulls, and the ir allies. Nine plumage-maturation characters were identified, and the ir states were superimposed onto topologies generated during two recen t investigations of shorebird relationships (Sibley and Ahlquist; revi sed Strauch). The characters were then optimized so as to assign chara cter states to interior nodes of the trees in the most parsimonious wa y.Reconstructions of character evolution on six of the shortest revise d Strauch trees were ambiguous with respect to delayed plumage maturat ion in the hypothetical ancestral shorebird. If plumage maturation was not delayed in the shorebird ancestor, optimization indicated that de lay appeared when nonadultlike juvenal feathers were acquired. In cont rast, on the single Sibley and Ahlquist tree, absence of delayed pluma ge maturation in the shorebird ancestor was indicated unambiguously, w ith three evolutionary novelties (nonadultlike juvenal feathers, seaso nal plumage change, and a reduced first-spring molt) implicated in its acquisition. Optimization indicated that delayed plumage maturation i n shorebirds can be explained plausibly without invoking selection for distinctive first-winter or fist-summer appearance. Two of the novel conditions generating delayed plumage maturation (modified juvenal fea thers and seasonal plumage change) did so only because they were acqui red in a taxon possessing restricted first-year molts, which are primi tive. Given these observations, it seems simplest to explain the delay in plumage maturation as an incidental consequence of the phylogeneti c inertia of shorebird molts. The third novelty that generates delayed plumage maturation, a reduced first-spring molt, may have been acquir ed to reduce molt-associated energetic demands in young birds.