FIELD STUDY IN ORNITHOLOGY. 477 



tlieir stations punctiiall}^ on a given day, as if their movements were 

 regulated by clock-work. In like manner, whether the summer be cold 

 or hot, the swiftrS leave their summer home in England about the first 

 week in August, only occasional stragglers ever being seen after that 

 date. So in three different years I noticed the appearance of the com- 

 mon swift {Gi/2>'^ehis apus) in myriads on one day in the first week in 

 April. In the case of almost all the land birds it has been ascertained 

 by repeated observations that the male birds arrive some days before 

 the hens. I do not think it is proved that they start earlier; but being 

 generally stronger than the females, it is very natural that they should 

 outstrip their wejilcer mates. I think, too, that there is evidence that 

 those species which have the most extended southerly, have also the 

 most extended northerly range. The same may hold good of individ- 

 uals of the same species, and may be accounted for by, or account for, 

 the fact that, e. //., the individuals of the wheatear or the willow wren 

 which penetrate farthest north have longer and stronger wings tlian 

 those individuals which terminate their journey in more southern lati- 

 tudes. The length of wing of two specimens of Saxicola amanthe in my 

 collection from Greenland and Labrador exceeds by 0-G inch the length 

 of the Briti.sh and Syrian specimens, and the next longest, exceeding 

 them by 0-5 inch, is from the Gambia. So the sedentary rhylloscopus 

 trockilns of the Canaries has a perceptibly shorter wing than European 

 specimens. 



To say that migration is i^erformed by instinct is no explanation of 

 the marvellous faculty; it is an evasion of the diflBculty. Prof. Mobius 

 holds that birds crossing the ocean may be guided by observing the 

 rolling of the waves, but this will not hold good in the varying storms 

 of the Atlantic; still less in the vast stretch of stormy and landless 

 ocean crossed by the bronze cuckoo {Chrysococcyx lucidna) in its pas- 

 sage from ISTew Guinea to New Zealand. Prof. Palmen ascribes the due 

 I)erformance of the fiight to experience, but this is not confirmed by 

 field observers. He assumes that the flights are led by the oldest and 

 strongest, but observation by Ilerr Gatke has shown that among 

 migrants, as the young and old journey apart and by different routes, 

 the former can have had no experience. All ornithologists are aware 

 that the parent cuckoos leave this country long before their young ones 

 are hatched by their foster-parents. The sense of sight can not guide 

 birds which travel by night, or span oceans or continents in a single 

 flight. In noticing all the phenomena of migration, there yet remains 

 a vast unfilled region for the field naturalist. 



What Prof. Newton terms the sense of direction, unconsciously 

 exercised, is the nearest approach yet made to a solution of the prob- 

 lem. He remarks how vastly the sense of direction varies in human 

 beings, contrasting its absence in the dwellers in towns compared with 

 the power of the shepherd and the countryman, and, infinitely more, 

 with the power of the savage or the Arab. He adduces the experience 



