REVIEWS. 348 



home " are similar to those of our winter visitors to Britain " 

 — we should not have thought that the two were in the least 

 comparable. 



We quite agree that the supposition that some birds are 

 wintering here during our summer and have bred in the 

 Southern Hemisphere during our winter, is hardly supported 

 by known facts, but we do not agree that it is even a 

 " possible explanation " of the presence of sexually mature 

 non-breeders in our breeding-season, as it seems highly 

 improbable that any bird should breed in its winter-plumage. 



Mr. Coward seems to scout much of Giitke's work, but 

 one must always realize that Gatke lived in an " area of 

 concentration " of bird-migration, and consequently had 

 unique opportunities of observation, and although he was 

 prone to exaggerate and build up theories on insufficient data, 

 his labours and enthusiasm did so much to stimulate the study 

 of migration, that his statements must not be rashly set aside 

 for those of others with less experience. Thus, Mr. Coward, 

 after dealing rather hardly with Gatke 's statements, appears 

 to accept (page 45) that of another observer who " for forty 

 hours " was " passing beneath the lines of an army of 

 (unseen) migrants, say 500 miles in width." 



The height at which birds migrate has always been a 

 source of speculation, and we do not consider it at all proved 

 that birds fly at the great altitude with which they have 

 been credited. The well-known and ^praiseworthy efforts of 

 the American observers to estimate the height by observations 

 through astronomical telescopes must, we think, be open to 

 doubt. The reviewer some years ago \^atched through the 

 Northumberland telescope in the Cambridge University 

 Observatory migrating birds passing across the moon, but 

 found that when it came to calculating the altitude of the 

 bird, a very small inaccuracy in estimating the apparent 

 and actual size of the object made a very great difference 

 in the result. 



Dealing with that mysterious faculty of birds called 

 " orientation " — if there be such, and we see no better 

 explanation — the author quotes the extremely interesting 

 experiments of Dr. Watson with the Sooty and Noddy Terns 

 at the Tortugas, but tells us also not too convincing a story 

 of the " homing " of a farm-yard duck. The recognition 

 of land-marks by migrating birds is also said to be a 

 guide, but it seems hardly necessary, if a bird can find its 

 way for the first time by " orientation," that on succeeding 

 journeys it should be helped by familiar landmarks. Besides, 



