8 BRITISH BIRDS. [vol. xiii. 



it seems as if the old bird begins to incubate as soon as the first 

 egg is laid, and that the eggs are not laid on alternate days 

 as I have stated in a previous paper.* The Bittern does not 

 always trouble about the later eggs. In 1918 there were 

 several left derelict in the various nests I saw. These when 

 broken contained perfectly formed young. Frequenth^ also 

 the youngest Bittern, being so much smaller and weaker than 

 his brethren, comes to grief. The young are very strong and 

 active when two or three days old and also very pugnacious. 



From the fact that the female does not always bring off 

 the entire clutch, and also because the male booms most of 

 the day some distance from the nest, I doubt very much 

 whether the males take any share in feeding the young. Both 

 this season and last, the males as soon as the young were a 

 few days old, went away from the nesting area and frequented 

 reed-beds much farther off. 



This season there seems to be a scarcity of male Bitterns. 

 It is possible when this is the case that the Bittern may be 

 polygamous, but so far the evidence is not absolutely conclu- 

 sive. In one reed-bed three nests have successfully hatched 

 off, while only one male has boomed there, and only one has 

 so far been flushed. But last year it took me some time to 

 discover two males in the same reed-bed where two females 

 had nested. Bitterns seldom boom together. They challenge 

 each other, and one after another responds until all the males 

 whose localities I can vouch for, have boomed in turn, and 

 then the first strikes up again. Therefore, if there were 

 several males in one small area booming in turn it would not 

 always be possible to differentiate between them. 



During the period prior to incubation the female sometimes 

 utters a soft booming sound when her mate is near. It is not 

 a deep resonant boom like that of the male, but a subdued 

 " wumph, wumph," akin to the contented grunt of a female 

 Water-Rail when the male approaches. 



Owing to their extreme furtiveness. Bitterns are perhaps 

 more difficult to watch than any other birds. It needs weeks 



* Transactions of the Norfolk and Norwich Naturalists' Society, 1918. 



