THE STRUGGLE FOR EXISTENCE. 207 



Wrens, and Tits, there is every reason to believe, 

 occasionally lay their eggs in the nests of other 

 birds of their own species, and, in the case of the 

 first-named two, I have found them mixed together 

 in the same nest. 



With a view to testing how far certain birds 

 will tolerate the eggs of others of a different species 

 in their nests, I commenced a series of experiments 

 last spring in the neighbourhood of Elstree. I dis- 

 covered that a Thrush will take no notice whatever 

 of the introduction of a Blackbird's egg to her nest, 

 and that the latter bird is equally indifferent to an 

 exchange with her lighter-coloured neighbour. I in- 

 tended to endeavour to carry out the exchange to 

 entire clutches, but, unfortunately, my experiments 

 were all ruined by Carrion Crows and mischievous 

 boys, of which we can boast a goodly number in 

 our particular corner of Hertfordshire. 



As some indication of the great struggle for 

 existence going on amongst birds, I have, from 

 close observation and a pretty extensive experience, 

 little hesitation in saying that I do not believe that 

 one-third of the eggs laid by British wild birds, 

 preserved and otherwise, ever produce in any 

 single season chicks which have the good fortune 

 to grow to adults. Egg collectors, schoolboys, and 

 savage destroyers who despoil for the mere love of 

 annihilating the beautiful ; table and manufacturing 

 requirements ; bird-catchers who take clutches of 

 young song-birds; Eagles, Falcons, Hawks, Owls, 

 Ravens, Crows, Eooks, Magpies, Jays, and Gulls; 

 foxes, dogs, cats, rats, stoats, weasels, and snakes ; 

 bad weather and accidents all claim a tithe either 

 of sitting hens, eggs, or young birds. 



Some birds' eggs and young have to trust for 

 protection entirely to their close harmonisation with 



