...They also frequently lay in nests where incubation has actuallybegun... 
P. L. Sclater 「Argentine Ornithology, Volume I (of 2)」
...The period of incubation is 28 daysbut 2 days more should be added to this to allow forcleaning out the machines, etc...
Harry M. Lamon 「Ducks and Geese」
...All the eggsintended for incubation purposes are sounded bystriking them gently against one another in order todetect and remove the cracked eggs...
Harry M. Lamon 「Ducks and Geese」
...The period of incubation ofgoose eggs is approximately 30 days, but may varyfrom 28 to 33 or occasionally even 35 days...
Harry M. Lamon 「Ducks and Geese」
...She will cover nine eggs, and incubation will last amonth...
Robert Jennings 「Sheep, Swine, and Poultry」
...The autumnal eggs afford useful employmentto turkeys and hens that choose to sit at unseasonable times; and theperiod of incubation is less tedious than that required for the eggs ofsome other birds...
Robert Jennings 「Sheep, Swine, and Poultry」
...The period of incubation isabout four weeks...
John H. Robinson 「Our Domestic Birds」
...The period of incubation for guinea eggs is four weeks...
John H. Robinson 「Our Domestic Birds」
...The period of incubation is fromtwenty-two to twenty-four days...
John H. Robinson 「Our Domestic Birds」
...The means of treating it at its different periods, from the periodof incubation to that of its decline...
Honoré Bourguignon 「On the cattle plague: or, Contagious typhus in horned cattle. Its history, origin, description, and treatment」
...The horned cattle composing this latter class must becarefully watched, and be made the subject of the preventive treatment,the moment the first sign appears of the working of the incubation...
Honoré Bourguignon 「On the cattle plague: or, Contagious typhus in horned cattle. Its history, origin, description, and treatment」
...Most birds, whenseized by the mania of incubation, will sit upon anything which evenremotely resembles an egg...
Douglas Dewar 「Birds of the Indian Hills」
...The male bird assists the female in performing the office of incubation,and is said to relieve the monotony of his occupation by singing,thus often betraying a well-concealed nest...
Rev. C. A. Johns 「British Birds in their Haunts」
...From two to four eggs are laid, bothmale and female taking part in the incubation...
Rev. C. A. Johns 「British Birds in their Haunts」
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