( 330 ) 

 NOTES ON MORTALITY IN NESTLING-CLCKOOS. 



BY 



J. H. OWEX. 



During the last few summers I have paid special atten- | 

 tion to the development of the nesthng-Cuckoo {Cuculus \ 

 c. canorus), and have been very lucky in finding plenty 

 of Cuckoos' eggs and young Cuckoos, but in other ways , 

 I have not been equally fortunate. A large proportion | 

 of the eggs disappeared during incubation, though not 

 by the hand of man. This was obvious, because the | 

 eggs in the nest were taken one by one, and curiously \ 

 enough the Cuckoo's egg, the largest in the nest, was | 

 invariably the first egg taken. Last year another ele- 

 ment of " luck " was against me, for in each of five 

 nests I found a solitary egg, and that a Cuckoo's, and 

 in every case the victimized bird deserted it. In another I 

 case the Cuckoo turned out all the Sedge-Warbler's eggs, 

 and the Sedge-Warbler, after incubating the Cuckoo's 

 egg for nearly eight days, finally deserted it. Three 

 nests were also destroyed by Jays. 



When the young Cuckoos hatched they were apparently I 

 no safer than the eggs. The number which failed from ! 

 various causes to grow up, was far nearer fifty per ] 

 cent, than forty of those found. In this estimate I only ! 

 reckon birds of which I have definite records in the 

 nest, and do not take into account young Cuckoos which 

 had left the nest a day or two. I have also omitted 

 from the following lists three young Cuckoos which ^^•ere 

 reared in 1911, as I am fairly certain they were removed , 

 by country boys and afterwards died, and for the same 

 reason I do not include two 1912 birds. 



Lists of nestlings are appended for 1911 and 1912. 

 Where it is stated that the bird was removed it must 

 be understood that it was destroyed before it was old : 

 enough to leave the nest. Number 9 in 1911 ejected 

 the Tree-Pipit's eggs, and I have in the Felsted School i 

 Museum an infertile egg ejected by the young Cuckoo. ] 

 Number 10 (1911) furnished me with some amusement j 



