THEIR REPRODUCTION (EGGS) 285 



lessen the period of incubation, but often 

 prove detrimental to the life of the embryo. 

 According to the observations of Mr. Evans 

 {Ibis, 1 89 1, pp. 52-93), and the many facts relat- 

 ing to incubation collected by him, the smaller 

 Passeres hatch their eggs in from twelve to 

 fifteen ' days, the larger species, including the 

 Raven, in nineteen or twenty days. The Crow 

 family are apparently the longest incubators 

 in the order, as of course they are the largest 

 species. In the Coraciiformes the period may 

 be slightly longer, but some of the Humming- 

 Birds are said to hatch their eggs in ten or 

 twelve days, whilst the Rollers, Kingfishers, and 

 Woodpeckers take from eighteen to twenty. 

 In the Owls the period of incubation is a long 

 one, ranging from twenty-six days in the Long- 

 eared Owl to thirty-three in the Eagle and 

 Snowy Owls. The Birds of Prey in some 

 cases are know^n to occupy from four (in the 

 Kestrel) to five weeks (in the Eagle). The 

 Condor is said, however, to take fifty-four 

 days. The Gannet takes nearly six weeks ; the 

 Cormorant about a month. The Herons vary 

 from about seventeen days in the smallest 

 species to twenty-five days in the larger, whilst 

 the Stork is said to occupy thirty days. Among 



