VOL. VI.] STUDIES IN BIRD MIGRATION. 81 



takes it for granted that all late migrants in spring are birds 

 which are on passage for breeding-quarters further north, 

 but evidence is slowly accumulating to show that this is not 

 invariably the case, and that some individuals arrive late 

 and breed in the south of England long after others of the 

 same species are breeding there and even further north. In 

 the same way he thinks that the early immigrants are " home 

 birds ■' ; this we think is almost impossible to prove, and 

 furthermore accompanying them sometimes are Continental 

 species, e.g. Redwing (Feb. 19th). With these chapters are 

 two maps showing the advance of the isotherm of 48° F. north 

 in spring and south again in autumn, and the author points 

 ■out the relation between the arrival of summer birds in one 

 area and the coincident advance of this isotherm, which, 

 moreover, makes it quite clear why these migrants are first 

 seen in the south-west ; again, in autumn a drop in the 

 temperature acts as a direct incentive to start the migrating 

 movement from further north. 



In three appendices connected with these chapters are given 

 first and average dates of arrival of summer and winter visitors 

 and the periods of migration of passage birds. The usnal 

 •date of first arrival in England of summer visitors is, in our 

 •opinion, in some cases given too early, particularly in those of 

 the Yellow Wagtail, Willow- and Wood-Warblers, and House- 

 Martin, Avhile the dates for both summer and winter visitors 

 must much depend on locality, and none is specified ; doubtless 

 as more reliable records are obtained for some of the scarcer 

 species, or species which come little under notice, the dates of 

 passage will l)e amplified. 



An important chapter is that dealing with the influence 

 ■of meteorology, and Mr. Clarke has been fortunate to obtain 

 the assistance of Dr. Shaw of the Meteorological Office. The 

 author starts by pointing out that it is the weather conditions 

 at the point of deparhire of the migrants which must be looked 

 at to solve the question of weather influences on migration, 

 and from a mass of statistics he has come to several important 

 and reasonable conclusions. Firstly, that when there is an 

 anticyclonic centre lying over the continent which extends to 

 ■our shores, the North Sea is spanned by settled weather and a 

 south-eaasterly tvpe of weather prevails ; this is the most 

 favourable weather for passage of migrants between Great 

 Britain and the Continent ; if however the favourable condi- 

 tions do not reach our eastern sea-board, then, although favour- 

 able for a start, bad weather and consequently " wreckage " 

 •ensues on approaching England. Secondly, the opposite kind 

 'of weather, that is an anticyclonic centre covering most of 



