SWIFTS AND SWALLOWS 9 



chasing flying insects, and the anatomical characters 

 of the Swifts differ from those of the Swallows, 

 which present no important internal differences 

 from the ordinary small passerine birds^ There 

 are small differences also in external characters 

 which are not to be correlated with modes of living ; 

 the Swifts have but ten tail-feathers to the Swal- 

 lows' twelve, and have not the scales on their shanks 

 which are usual in birds. There is also a conspicuous 

 difference in habit which seems to have no relation 

 to utility, and hence is more likely to be a family 

 character ; in flight the Swallow every now and 

 then draws in its wings to its sides it still shows a 

 sign of the typical small passerine bird's flight 

 with its occasional dips with closed wings while 

 the Swift always keeps its wings fully expanded, 

 whether skimming motionless or renewing its 

 impetus by means of wing-beats. 



Small details of habit are thus always worth 

 observing, as they may be more significant than 

 they seem, and in any case are good practice in 

 observation. 



Some pitfalls in observation or in drawing con- 

 clusions from the same need mentioning in con- 

 clusion. The danger of the major habits becoming 

 modified in captivity or domestication has been 

 alluded to, and is, indeed, made rather too much of 

 by some writers ; still, it is well to bear it in mind. 

 There is also the difficulty of the field observer in 

 discriminating between individuals often between 

 the sexes, when these are alike. One must never 



