74 BULLETIN 17 6, UNITED STATES NATIONAL MUSEUM 



average 27.18 by 20.57 millimeters; the eggs showing the four ex- 

 tremes measure 30.48 by 22.86, 22.61 by 18.80, and 25.40 by 18.29 

 millimeters. 



Young. — Incubation is shared by both sexes and lasts for about 14 

 days. As the eggs are often laid at infrequent intervals, it is not unus- 

 ual to find j'^oung birds of different ages, or even eggs and young, in 

 the same nest. Both sexes assist in the care of the young and are 

 devoted parents ; even when an egg is hatched by a foster parent, the 

 mother cuckoo does not seem entirely to lose interest in her young- 

 ster, as related above. On the other hand, William H. Moore (1902a) , 

 of Scotch Lake, New Brunswick, says: "I have known this bird to 

 desert its young when the nest was molested, and after the young 

 died they were covered with leaves by the adults." Cuckoos are care- 

 less about removing the cast-off shells, which are often found in the 

 nest after the young have hatched. The young remain in the nest 

 7 to 9 days after hatching and then become quite precocial. While in 

 the nest the young are fed by their parents in a rather peculiar man- 

 ner, of which Dr. Thomas. S. Roberts (1932) writes: 



When the old bird returns, the food, which is very likely to be live cater- 

 pillars, is concealed in the throat. As a nestling raises its head with open 

 mouth and rapidly vibrating wings, the parent thrusts its bill deeply into the 

 open maw and the young bird grasps securely the smooth bill of the old bird, in 

 which action it is greatly aided by several soft papillae or disks in the roof of 

 the mouth. Then, with a slow, pumping motion, the squirming caterpillars are 

 transferred with some difficulty from one mouth to another. The process is a 

 slow one, the birds being attached a minute or more and the transfer aided, 

 apparently, by a sucking effort on the part of the nestling. 



When a young Cuckoo opens its mouth widely there are visible, in the rocf 

 of the mouth, a number of large, flat-topped, white papillae or tubercles, ar- 

 ranged symmetrically, the function of which is plainly to make it possible for 

 the nestling to maintain its hold on the parent's bill, which is smooth and 

 tapering. A small finger-tip inserted well down into the open, upturned mouth 

 of a nestling is seized tightly and a sucking motion is distinctly perceptible. 

 [PI. 10.] 



Prof. Francis H. Herrick (1935) has made a thorough study of the 

 home life of the black-billed cuckoo, and I cannot do better than to 

 quote a few of his remarks on the behavior of the young. After 

 describing the peculiar appearance of the newly hatched young, he 



says: 



More remarkable than anything about its appearance, however, is the muscu- 

 lar vigor and endurance the cuckoo displays at this tender age, for it seems to be 

 able to withstand heat, hunger, and general neglect that would be fatal to the 

 young of most wild birds. I soon found by experiment that when barely three 

 hours out of its shell this little cuckoo could hang suspended by a leg or even 

 by a single toe for upwards of a quarter of a minute, and that it could raise it- 

 self up until its bill was well over the twig that it grasped with both feet ; and 

 in a short time it was able to raise itself on to the twig, or even to draw itself 



