...7 nest on December 28 (incubationperiod thirty-four days)... 
George Murray Levick 「Antarctic Penguins」
...All the nests round abouthad eggs under incubation, and the pair in questionmust have been newcomers...
George Murray Levick 「Antarctic Penguins」
...They also frequently lay in nests where incubation has actuallybegun...
P. L. Sclater 「Argentine Ornithology, Volume I (of 2)」
...Period of Incubation...
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」
...They arenever seen near their homes during the day, the bird then on the nestwaiting until night to feed, when the one which has been at sea returnsto assume its share of the task of incubation...
Frank M. Chapman 「Color Key to North American Birds」
...The so-called period of incubation...
U.S. Department of Agriculture 「Special Report on Diseases of Cattle」
...In aërial birds (except the cuckoos) the maleand female pair, build a nest, and both take part in the incubation ofthe eggs and the feeding of the young...
John H. Robinson 「Our Domestic Birds」
...An infertile egg is clear, that is, shows no signs ofdevelopment or decay, at every period of incubation...
John H. Robinson 「Our Domestic Birds」
...Still another important development due to artificial incubation tookplace in California...
John H. Robinson 「Our Domestic Birds」
...The period of incubation is from thirty to thirty-five days...
John H. Robinson 「Our Domestic Birds」
...The period of incubation for guinea eggs is four weeks...
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 period of incubation for the koel's egg is shorter thanthat of the crow, hence at the outset the baby koel steals amarch on his foster-brothers...
Douglas Dewar 「A Bird Calendar for Northern India」
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