242 Proceedings of the Eoyal Physical Society. 



ins are those connected with the laws of the extension of 

 range in the breeding season, and closely allied to these, and 

 in part dependent upon them, the laws of migration, and the 

 distribution of species at different seasons. 



If, for instance, a species of bird appears with tolerable 

 regularity and in yearly increasing numbers during the autumn 

 migration or winter season at a locality, or in a district where 

 it had never been seen before, it is perhaps natural to sup- 

 pose that this distribution is due to a greater extension of the 

 breeding area. If, however, these occurrences are only fitful, 

 and not steady or increasing in numbers yearly, a more 

 natural supposition perhaps is that they are due, not to a 

 steady increase in breeding range, but to abnormal winds 

 occurring at the time of migration. 



It is quite true, however, that in many cases such pheno- 

 menal " rushes " of birds at long intervals upon our coasts 

 can be traced to an overflow at their headquarters, and such 

 there is every reason to believe was the cause of the vast 

 irruption of Pallas' Sand Grouse into Europe from the Siberian 

 plains in 1863. 



It is not my purpose here to go into the subject of all the 

 causes affecting the spread of species in the nesting season, 

 as such an inquiry would form materials for a separate essay 

 of no mean proportions, but certain causes will readily suggest 

 themselves to you, as I speak of the actual facts of the 

 extension of range of the present species — the stockdove 

 {Columba wnaSy Lin.). 



The specimen I show you this evening was obtained at 

 Gartmore in the south-west of Perthshire, and was forwarded 

 for me to Mr Small, George Street, by Mr C. C. Tunnard, 

 factor on Gartmore. It was obtained on the 1st January 

 1883, and since then he is almost certain he has seen more. 



The following notes have no pretensions to exhaustiveness, 

 but are intended merely to indicate the general lines. They 

 might as it were form a framework for a more exhaustive 

 account of the species and its travels. 



Of the distribution of the stockdove on the continent of 

 Europe, and of the probable prehistoric land-connection be- 

 tween our south-eastern counties of England and Holland, I 



