Molt patterns, age criteria, and molt-breeding dynamics in American Samoan landbirds

Abstract

We examined 135 specimens and analyzed 1,735 captures of indigenous American Samoan landbirds, of nine target species in seven families, to document molt patterns, assess the extent of molt-breeding overlap, and present criteria to determine age. Preformative molts varied from absent to complete, and there was no confirmed evidence for prealternate molts. Molt strategies, age-determination criteria, and remigial replacement sequences were largely consistent with those of other temperate and tropical bird species within the same families. Suspended and/or arrested molts were recorded in seven species and staffelmauser or stepwise molt in two species, including the first report in a passerine. Our data suggest that staffelmauser and suspension of molt in passerines may share a common underlying mechanism. Despite broad overlap of breeding and molting seasons at the population level, we observed little evidence of molt-breeding overlap at the individual level. We suggest that molt and accompanying restoration processes may take precedence over breeding, as indicated by well-defined molting seasons despite apparent year-round or bi-modal breeding in some of our species. Tropical landbird species appear to be capable of suspending molt to breed when environmental conditions shift to facilitate successful reproduction.