i74 
THE CUCKOO’S SECRET 
Cuckoo had shared the territory, and at the begin- 
ning of 1921 two other Cuckoos each laid an egg at 
either end of the area, but nothing more was seen 
of them. The Cuckoo which laid eleven eggs 
evidently drove them off the territory. 
In another locality a Reed Warbler Cuckoo 
produced four eggs and placed one of them in the 
nest of a Chaffinch * built in the same willow bush 
in which Chaffinches had a nest with a young 
Cuckoo in the previous season. This supports my 
belief that Cuckoos victimise the same individual 
foster birds season after season. Mr. Pettitt states 
there were only five pairs of her natural fosterers, 
and none of them had a nest in suitable condition 
at the time the Cuckoo deposited her egg in the 
Chaffinch’s nest. 
In a third area of a few acres, three Cuckoos 
attempted to establish themselves. The first- 
comer deposited an egg on June 2 in the only Reed 
Warbler’s nest then available. A second egg was 
found on June 14, but on the same day eggs of two 
other Cuckoos were found in one Reed Warbler’s 
nest. The area was not visited again until July 3, 
when I also was present, and together we found 
two eggs of one of the later Cuckoos, and also 
* FringiUa coelebs , L. 
