3' Q 8 NURTURE OF TTIKIR YOUNG. 



but their form ami arrangement vary considerably, as we have 

 elsewhere seen (A.viM. PHYSIOL., 7^4.) Nearly all Birds line 

 their nests with soft substances, which they collect with care, or 

 even with a thick and soft down, which they tear from their own 

 breasts. The warm and light sub.>tance employed in domestic 

 economy under the name of eider-down, comes from a kind of 

 duck named Eider (Fig. 293) ; which inhabits the isles of the 

 Arctic seas, and which thus strips itself to line its nest with the 

 down torn from its breast. 



.'151. Birds lay their eggs generally once, sometimes twice, a 

 year; in a *tate of domesticity their fecundity becomes greater. 

 The number of eofgs is greater in small species than in lar^e 

 ones ; Eagles lay only two or three at each season; Tomtits and 

 \Vrens from fifteen to twenty. The constancy with which Birds 

 sit on their eg'_ r s is admirable ; sometimes the two parents divide 

 this labour between them ; in other ea-es the male is satisfied 

 with providing for the wants of the female, while she is sitting : 

 and in other species, the whole charge of the incubation rest- on 

 the mother alone. In jjeneral it is only with reluctance, and 



G 



when urged by hunger, that she quits her offspring for a few 

 minutes ; and when her young ones are hatched, her maternal 

 affection leads her to lavish on them the most tender cares ; 

 she covers them with her wings to protect them from the cold, 

 and brings them carefully-selected food, which she often disgorges 

 into their throats, after having half-digested it, to render it 

 more suitable to their tender stomachs. She guides their i'uvt 

 steps ; teaches them ii) use their winirs ; and when danger 

 threatens, shews in saving them as much courage as devoted- 

 ness, we may almost say intelligence. There are however some 

 Birds, that lay their e^s in nests which do not belong to them, 

 in order to have them hatched hv strange nurses : such as the 

 Cuckoo, which lays its eg'_ r s in the nests of Thrushes, Yellow- 

 hammers, Blackbirds, or an v other insectivorous Birds, accustomed 

 to feed their young with what would be suitable for the young 

 Cuckoos ; and (which is a remarkable circumstance) the foster- 

 mother becomes a tender and indefatigable parent to these 

 intruders, although they deprive her of her own offspring. Some 

 naturalists as.sert that the old Cuckoos take care to destroy the 



