Hayes, F. E. 2002. Geographic variation, hybridization, and taxonomy of New World Butorides herons.
North American Birds 56:4-10.
Abstract.--The New World Butorides herons comprise three distinct forms whose taxonomy has been debated: the rufous-necked Green Heron (B. virescens) of North America, Central America, and the West Indies; the gray-necked Striated Heron (B. striatus) of South America and the Old World; and the dark Lava Heron (B. sundevalli) of the Gal�pagos Islands. An extensive analysis by Payne (1974) concluded that they interbreed freely where their ranges meet and should be considered conspecific. However, Monroe and Browning (1992) alleged that Payne's voucher specimens used as a hybrid index for B. virescens and B. striatus included juveniles and did not represent a continuous series; they concluded that B. virescens and B. striatus rarely interbreed and were specifically distinct. My reexamination of Payne's voucher specimens revealed that all had attained adult neck coloration and represent a continuous series. My reanalysis of Payne's data demonstrates increased variability and intermediacy in the contact zone between B. virescens and B. striatus, implying extensive hybridization. However, the presence of apparently pure B. virescens and B. striatus phenotypes within the contact zone suggests that assortative mating does occur, supporting the treatment of the two forms as distinct species. Similarly, the persistence of pure B. sundevalli in a potential hybrid zone with B. striatus in the Gal�pagos Islands supports its treatment as a distinct species. Further information is provided on molts and plumages of Butorides herons. |
