130 



The Bird 



When we sought the extreme in the provision of saHva 

 in birds, we had to refer to a swift, Uving in caves in 

 islands of the Malay Archipelago, but to find the highest 

 degree of development of crops is a much easier matter. 

 In the ordinary pigeon the crop is of \'er}' great size 

 and divided into two lobes. The capacity of the crop 

 in some birds of this class is astonishing. As many as 

 sixty-three acorns have been found in the crop of the 

 English Wood-pigeon. If we look at the crop of a pigeon 

 before its A'oung leave the nest, we will discover a func- 

 tion of this organ which would otherwise never be sus- 

 pected. We know that herons and some other birds 

 feed their young on fish half-digested by themselves. 

 This process is known as regurgitation. If we have ever 

 seen a pigeon with the beak of its young half down its 

 throat, pumping something into the offspring's mouth, 

 we have probabl}' thought that a similar habit was being 

 shown, — half-digested grain taking the place of the 

 heron's fish. But such is not the case. At the time 

 of the breeding season, the folds of membrane in the 

 crops of both parent pigeoas thicken and secrete or 

 peel off in curdy cheesy masses — "pigeon's milk" some 

 call it — and this forms the food of the young birds So 

 in pigeons the crop not only receives food, but at times 

 provides it. 



Now for a glance at some of the oddities in the struc- 

 ture of crops. The Hoatzin — a strange bird of Brazilian 

 swamps — which harks back to its reptihan ancestors in 

 many ways, has a very curious crop. There are strong 

 muscles in its walls, the use of which, it is said, is to 



