1 92 1. BuRKiTT. — Song and Nesting of Birds. 119 



the iith and 24th April, and by the first days of May the 

 greatly increased number of Thrushes which sang either 

 at dusk or dark dusk, made the singers so close together 

 that one could not hope to tell with certainty to which 

 territory or nest each singer might belong. I had therefore 

 to regretfully conclude that further observations in such an 

 area on the relation of song to nesting were futile. 



I took therefore no more notes till June 5th when I 

 found there was no dusk song whatever around me. I do 

 not know when it ceased. There were still a few songs in 

 the day and a few in the evening. June 22nd was the last 

 date I heard a single song in the country. (I noticed a 

 Thrush badly moulted on June 28th). 



The early song of January and of three weeks of 

 February, followed by the comparative silence of March 

 and part of April, and the rising again to a high volume 

 and great numbers towards the beginning of May seems to 

 indicate (as one feels at the time) that there must be a great 

 immigration in the latter period. I had not been aware 

 of such immigration, but I have since been told that it is 

 probable. The normal early nesters would be free to start 

 new nests early in May and therefore, perhaps, to join in 

 this May song, but this is only gues^-; work. A certain amount 

 of second brooding is evident. 



The relation of song to nesting in the May birds may 

 be different to that of the early birds, but I have to leave 

 the solution of this to observers who have much fewer 

 Thrushes than I. Some very late Thrushes which had 

 young hatched out about June 8th had certainly not 

 sung for a long time before that and did not sing after- 

 wards ; what then was the meaning of the singing birds 

 who continued to the 22nd, unless they were niateless ? 

 The time of day in which these birds sang would be 

 parallel to the early unmated birds. Therefore probably 

 this June song, like the Chaffinch's, js of the type I call 

 " residual " below. I have not referred to mateless birds 

 much, because the early birds seemed to be all mated 

 except a couple of males within half a mile radius of 

 me who remained singing and apparently mateless and 

 maintained their day song for from 15 to 28 days — quite 



