DOMINATING CUCKOOS 187 
conditions in which, in two consecutive seasons, 
the same two Cuckoos lay concurrently in nests 
of the same species of fosterers on one and the 
same territory. 
In the second season there was quite a different 
state of affairs. A had developed her full powers 
and become a truly dominant bird. She kept the 
common entirely to herself until she had finished 
laying, and then, and not until then, B was allowed 
to enter and deposit two eggs. In the third year 
(1920) we found an egg of B on May 15 in the nest 
of a Linnet with three of the rightful eggs, and 
that was the only trace of her seen throughout the 
season. 
But later in the same year 1920 an entirely new 
Cuckoo, F, came to the common, and had before 
noon on June 14 deposited an egg in a Meadow 
Pipit’s nest, since it had been victimised by A with 
her sixteenth egg on June 12. A reference to the 
detailed notes for that period will show that this 
was about the time of the crisis in A’s domestic 
affairs, and her vigilance was no doubt so far 
relaxed as to afford F the opportunity to slip in and 
use unmolested a nest for which A had no further 
need. Cuckoo F also laid one only out of six eggs 
found on another common within ten days 
