308 THE ZOOLOGIST. 



one hundred yards of this an exactly similar egg in the nest of a 

 Blackcap (S. atricapilla) , the two eggs undoubtedly belonging to 

 the same bird. One egg of the rightful owner is removed by the 

 Cuckoo from the nest she has selected to receive her own, but 

 whether this is done before her own egg is laid or afterwards I 

 am not sure. The fact that only one egg is removed shows that 

 the Cuckoo is no egg-eater ; probably the egg is carried away to 

 some distance and then dropped, for I have never been able to 

 find any trace of the remains of the discarded egg anywhere 

 near the nest. I have found (though I think it unusual) a fresh 

 Cuckoo's egg among a clutch that has already been incubated for 

 some days. Such cases point to the Cuckoo's egg requiring a 

 very short period of incubation, for if the other eggs in the nest 

 were hatched some days before the Cuckoo, it seems reasonable 

 to argue that the young receiving warmth and food would gain 

 sufficient strength to resist the young Cuckoo when it appeared ; 

 yet we all know that the young Cuckoo invariably becomes the 

 sole occupant of the nest. As a rule, the egg is deposited before 

 the foster-parent's clutch is complete ; generally about the time 

 there are two or three eggs in the nest. One nest of a Eeed- 

 Warbler I found appeared completed, but contained no eggs. Six 

 days later there were three Keed-Warbler's and a Cuckoo's egg. 

 When blown all showed signs of embryo. The young Cuckoo is 

 by no means a lovable bird ; it snaps and mouths around at 

 everything that goes near it, and it is often a most laughable 

 sight to see it when it has outgrown its foster-parent's nest, 

 squatting on the remains, and mouthing in all directions, Yet 

 the foster-parents — no matter of what species — always show the 

 utmost affection for their alien child, whose hunger never seems 

 able to be satisfied. We know that the adult Cuckoo often starts 

 on the return migration while young birds and even eggs are still 

 to be found in various nests. With whom, then, do the young 

 Cuckoos migrate ? Do the single nestlings seek out others of 

 their kind, and migrate together in small parties ; or is the 

 hereditary instinct so strongly developed in each individual that 

 they undertake the journey alone ? They cannot migrate in 

 company with their foster-parents, as these are often resident 

 species, as is the case of the Eedbreast, Hedge- Sparrow, Pied 

 Wagtail, &c. These and many other points make the Cuckoo a 



