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
A monograph of the Trochilid, or family of humming-birds /.London :Printed by Taylor and Francis ;1861 [i.e. 1849-1861].biodiversitylibrary.org/page/35246209