PARENTAL CARE AND NEST-MAKING 311 



nests, so the cuckoo may build none. Just as the courtship 

 period, which normally stops as brooding begins, may be 

 lengthened out abnormally, so the cuckoo may shorten down 

 its brooding to nil. A lack of time-keeping or attunement 

 between egg-laying and nest-building is casual in many 

 birds ; it occurred as a variation in the ancestors of the 

 European Cuckoo and became established as a racial 

 peculiarity because it was congruent with some other 

 peculiarities of constitution and habit, and because it was 

 found to work well. 



§ 7. The Case of the Mound-Birds 



Incubation may be skipped altogether, but this does not 

 necessarily imply the absence of parental care. The most 

 instructive case is that of the Mound-Birds of Borneo and 

 other parts of the Far East, technically called megapods 

 {Megapodius) because of their heavily built legs, which are 

 capable of very vigorous digging. 



One of these birds, the maleo of Celebes, often makes its 

 nest in the dry volcanic sand near the shore. A pair of 

 them dig a hole about a yard deep and a yard in diameter, 

 and in this the mother-bird lays an egg and covers it with 

 sand. They then return to the forest. At intervals, 

 however, extending over a considerable time, they come back 

 to the shore, and the hen lays egg after egg till there are eight 

 or more. Then the hole is filled up and the precious pair 

 retire for good to the shelter of the trees and trouble no more 

 about the matter. There is perhaps no food for them near 

 at hand, and in any case there is no need for them to stay. 

 The warmth of the sun-baked dry sand is sufficient to ensure 

 the development of the embryo, and the sand is loose enough 

 to let air in to the eggs. It must be an awkward place to 

 be born in, beneath the ground, but the young mound-birds 

 manage to struggle out safely. Some young mound-birds 

 are unique in being able to fly on the day of their birth, but 

 it is said that the young maleos are only able to run. In 

 any case, running or flying or both, the newly hatched 



