286 THE STORY OF THE BIRDS 



the Ducks we have a range of from about 

 twenty days in the smaller species to thirty 

 days in the Geese, and from thirty-five to 

 forty days in the Swans. The Typical Pigeons 

 range from about fifteen to seventeen days, 

 the largest species in the order a month. The 

 Sand-Grouse incubate in a little over three 

 weeks to a month. In the Galliformes the 

 smaller species like the Quail take about three 

 weeks, the larger species a month. This is 

 also about the limit in the Charadriiformes 

 and the Lariformes. The Petrels are longer, 

 the smaller species taking about five weeks ; 

 the larger, such as the Albatrosses, eight or 

 nine weeks. The Auks take more than a month 

 (thirty to thirty-five days) ; some of the Im- 

 pennes are said to occupy six weeks, whilst 

 the Emu requires a couple of months, the 

 Rhea two weeks less, and the Ostrich takes 

 from seven to eight weeks, or even more. In 

 some species incubation commences as soon 

 as the first egg is laid ; in the majority of 

 cases, however, the process does not begin 

 until the last egg of the clutch or sitting is 

 deposited. As we have already seen the female 

 in most cases is the principal incubator ; in 

 some instances both sexes incubate in turn ; 



