BIKD SOCIOLOGY 127 



eighteen hours in the day. Now if they feed their young 

 for eighteen hours, the latter presumably require it ; but 

 in a southern country, where the day is only twelve hours 

 long, they would perforce have to fast for twelve hours. 

 I take it that migrant birds originally lived in one place 

 throughout the year, but those who went a little further 

 north to breed reared stronger nestlings owing to the 

 longer summer day, and so had a slight advantage in the 

 struggle for existence. Of these the individuals who 

 moved south in winter when insect food became scarce 

 gained a further advantage, so that gradually the non- 

 migrants at either end were eliminated. Moreover, the 

 further the migration was pushed within certain limits 

 the greater was the advantage. This theory has at least 

 the merit of assuming a gradual and uniform development 

 of the migratory instinct in place of the sudden revulsion 

 postulated by Professor Thomson. Furthermore, I do 

 not see how the " organic reminiscence," which took the 

 professor's birds back to their " original headquarters 

 before the Ice Age," came to act in the reverse direction 

 with the approach of autumn. As regards the height at 

 which the migrants fly, is it not probable that, like 

 balloonist s, they seek the level at which there is a strong 

 current blowing in the desired direction? This would 

 also account for the rapidity of the journey. 



E. C. STOWELL. 



October 7, 1911. 



NOTE. I think that Mr. Stowell's very interesting 

 theory tends to look upon migration as an acquired 

 character, rather than a constitutional impulse (though 

 aptitude supplements the germinal capacity), to over- 

 emphasize the food question and to ignore not only the 

 high degree of punctuality in migratory movements but 

 the something of sublimity in them : " The stork in 

 the heaven knoweth her appointed times ; and the 

 turtle and the crane and the swallow observe the 



