INTEBBBEEDING OF SONG-THBUSH d BLACKBIBD. 195 



have always found that the male bird has the influence over the 

 external appearance of the shell of the egg. 



As I was again visiting the district this year, I found two 

 identical eggs in a last season's nest. I am unable to say 

 whether or not the nest was the same used by the pair in 1910. 

 The eggs were quite cold, and no bird visited the nest. The next 

 day it was blown into the roadway, as the rain and wind had 

 loosened the foundations of the old nest. The eggs were, of 

 course, smashed, and their contents were in a perfectly liquid 

 state. 



The question naturally arises : " Do these hybrid eggs ever 

 hatch out, and, if so, whom do the nestlings resemble?" Mr. 

 Berry recorded in the 'Glasgow Naturalist' (vol. ii.) that no 

 difference could be seen between the young hybrids and young 

 Blackbirds. This, however, though not uncommon, is not always 

 the case. 



The birds produced from these hybrid eggs are almost always 

 ugly in appearance. They seem to be pre-eminently Thrushes, 

 but are sometimes uniformly darker, or darker in patches. 

 Very often they possess a Blackbird tail or beak, more often the 

 former. Although young Song-Thrushes are normally darker 

 than their parents, they are in no way so dark as are these 

 hybrids. 



The reason for this union, in nature, can hardly be the absence 

 of birds of the same species. In captivity. Thrushes and Black- 

 birds will invariably mate and interbreed. Again, the district 

 in which the birds are seems to affect interbreeding. I have 

 noticed this in Middlesex and Buckinghamshire, and in both 

 cases more than one pair of birds were interbreeding. In the 

 Edgware and Barnet district it is, I think, very noticeable, and 

 in both these districts the Song-Thrushes far outnumber the 

 Blackbirds. An account appeared in the 'Country Side' (vol. i. 

 p. 51) of a nest of hybrids at Stanmore, a village near Edgware. 

 The writer, finding Blackbird's eggs in a Thrush's nest, was 

 persuaded that the eggs were laid by stress of circumstances in 

 a Song-Thrush's nest. This, of course, occasionally occurs, but 

 I am rather inclined to think that this was another case of inter- 

 breeding in North Middlesex. 



The explanation often given that the female bird, being 



