A monograph of the Bucerotid, or family of the hornbills..[London]Published for the subscribers by the author [printed by Taylor and Francis]1882..biodiversitylibrary.org/page/38534569
The birds of North AmericaNew York :Published under the auspices of the Natural Science Association of America,1903. biodiversitylibrary.org/page/35159679Aquila chrysaetos use 9 different calls 2 communicate esp. when their young & food are involved! biodiversitylibrary.org/page/35159679 #bhlpod > thx @eol