...What a cheerful contrast is Bob White's clear, staccato whistle to thedrawing coo of the amorous dove! Character is often expressed in abird's voice as well as in ours... 
Neltje Blanchan 「Birds Every Child Should Know」
...Call, an explosive quab; song, a soft coo repeatedfour or five times...
Frank M. Chapman 「Color Key to North American Birds」
...A softly whistled coo repeatedmany times at intervals of about one second...
Frank M. Chapman 「Color Key to North American Birds」
...The coo is rapidly repeated, and is continued for several minutes; hence their name of Trumpeters...
Charles Darwin 「The Variation of Animals and Plants Under Domestication, Vol. I.」
...Brent, besides its peculiar note, used to coo in a singular and pleasing manner, which, independently, struck both Mr...
Charles Darwin 「The Variation of Animals and Plants Under Domestication, Vol. I.」
...In spring the male utters a note not unlike the coo of aWood-pigeon, which it repeats several times, and at other seasons itoccasionally emits a sound something like the shrill note of the Greenfinch...
Rev. C. A. Johns 「British Birds in their Haunts」
...The note of this dove is exceedinglyplaintive, and is softer, but much resembles the coo of the turtle-dove...
Charles Sturt 「Expedition into Central Australia」
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