THE LAYING OF CUCKOOS 183 
Cuckoo A. On each of the only two occasions 
in 1920 and 1921 when she laid an egg in a nest 
of a bird other than her natural fosterer, had she 
retained her egg one day longer, she would have 
been able to lay it in a nest of her natural fosterer 
in suitable condition, for which nest I believe such 
egg was intended. Observe, moreover, that the 
exceptional act of laying an egg in a Tree Pipit’s 
nest was promptly followed in each case by a break 
in the Cuckoo’s laying sequence. 
In other words, when a Cuckoo is forced to 
desert her natural fosterer, the stimulus to repro- 
duction is checked. Hence my belief that when 
a Cuckoo is driven from her natural fosterers by a 
more dominant Cuckoo she will not lay many eggs 
unless and until she becomes reconciled to the 
adoption of another species of fosterer. This is 
a line of inquiry I am anxious to see pursued. 
It can be readily understood that in the mean- 
time such a Cuckoo lays such eggs as nature 
demands, depositing them haphazard ; hence the 
exceptional cases of Cuckoos’ eggs being found 
fresh in nests containing eggs well advanced in 
incubation or even in nests from which the young 
have flown. I do not believe this possible in the 
case of a “ dominant ” Cuckoo. 
