ORNAMENTAL PLUME DEVELOPMENT AND THE “PREALTERNATE MOLTS” OF HERONS AND EGRETS

Abstract

Abstract To investigate molts and ornamental-plume development in herons and egrets, we examined 448 specimens of 10 North American species. We found no evidence for a prealternate molt, despite widespread opinion that such a molt occurs and includes the ornamental plumes. Our data indicate that these plumes emerge during the later stages of the definitive prebasic molt in August–November, grow slowly through January– February, and are retained until replacement during the following prebasic molt. The preformative (traditionally termed “first-prebasic”) molt shows substantial variation in extent. In 91.9% of 86 first-year individuals collected between November and May, this molt included the development of ornamental plumes that were similar in form, but shorter in length, than those of adults. Male Great Blue (Ardea herodias) and Little Blue (Egretta caerulea) herons developed longer ornamental plumes than females, presumably a result of sexual-selection strategies.