Recently published Ornithological Works. 313 



is this true of the velocity of the movements of the flocks on 

 migration, which Gatke calculates in the case of the Red- 

 spotted Bluethroat at some 45 geographical miles per hour. 

 This estimate is founded on the belief that the bird quits 

 Egypt at the end of April or beginning of May, while it 

 arrives in Heligoland at about the same time of year • so 

 that some 400 miles would be covered in one spring night of 

 perhaps 9 hours duration. Moreover, Gatke appears to have 

 believed that the flocks never, or hardly ever, rested by the 

 way. Now Herr Helm is at great trouble to shew that the 

 Blue-throat leaves Egypt in February or March, and proves by 

 many a record that it occurs in spring much more frequently 

 than has been hitherto believed in the intermediate districts of 

 Austria and Germany. It therefore has one or two mouths in 

 which to compass the journey. 



Again, as to the height at which the flocks travel, he 

 considers that former calculations may have been erroneous, 

 for he thinks that the state of the atmosphere has not been 

 sufiiciently reckoned for, and that it may produce delusive 

 eff'ects both upon the eye and the ear of the observer. 

 Sound travels very differently through different media, and 

 the distance of a bird may be extremely difficult to judge 

 correctly. The second article brings under consideration the 

 flight of Swallows, Carrier-Pigeons, and Ducks, with a 

 discussion of the efl'ects of temperature. 



57. Hudson's ' Birds and Man' 



[Birds and Man, By W. 11. Hudson, F.Z.S. London. 8vo. Longmans. 

 318 pp. 190L Price 6s. net.] 



This new volume of our friend Mr, W. H. Hudson's essays 

 on topics connected with bird-life will be of interest to 

 ornithologists as well as to the world in general. They relate 

 to such popular subjects as Daws, Ravens, and Willow- 

 Warblers, and to such familiar places as London, Wells, and 

 Selborne, but will be none the less appreciated by many of us. 

 The Dartford Warbler has deservedly a chapter to itself ; 

 Mr. Hudson found it still existing in four counties " in a few 

 widely-separated localities," but in spite of the " protection- 



