POSITION OF LEGS OF BIRDS DURING FLIGHT. 145 



is nearly always a long or frequently a forked tail, the forks of 

 which are similar in their action to the long legs of other species. 

 But mere soarers and gliders, of however powerful and enduring 

 flight, such as the Caihartidce or Vulturidce, should be clearly 

 distinguished from birds which twist and turn frequently, such 

 as the Swallow-tailed Kite (Elano'ides), or the Hirundinidce or 

 the CypselidcB. In the former there is no need for a forked tail, 

 a feature which is so frequent amongst the latter. Further, it 

 must be remembered that even amongst such constant fliers as 

 the Swallows, the power of flight is by no means of universally 

 equal strength amongst all the forms. The long wings, and 

 deeply forked tail, of our own Swallow represent an immense 

 gulf, as regards powers of flight, between it and such compara- 

 tively feeble fliers as the South African Cliff Swallow (Petro- 

 chelidon spilodera), in which both wings and tail are short, and 

 the tail square. 



I have been at the pains to bring together in a list, the majority 

 of swiftly or erratically flying families in which the tail is forked, 

 or the legs long, excluding on purpose such merely powerful and 

 sustained fliers as the Herons, Storks, Cranes, Vultures, Con- 

 dors, and the like. An examination of these shows that, while 

 the Fregatidce have all a forked tail, it is only in certain repre- 

 sentatives of other families that the fork is present, as in 

 Oceanodroma amongst the Petrels ; in Milvus, Lophoictinia, and 

 Elano'ides amongst the Falconidce ; in Glareola, in Xema, Hydro- 

 chelidon, Ncenia, and Rhynchops amongst the Gulls and Terns 

 and their allies ; in Dicrocercus amongst the Bee-eaters ; and in 

 certain of the Caprimulgidce, Cypselidce, Hirundinidce, and Hum- 

 ming-birds. In some forms, on the -other hand, the same pur- 

 pose seems to have been effected by the medium of two or more 

 elongated tail-feathers ; such are the Phaethontida, Stercorarius, 

 Merops, and Meropogon, and the males of some of the Nectari- 

 niidce. Amongst those which perform great feats of flight, yet 

 have no fork, the Diomedeince, Oceanitince, Procellariince, and 

 Pelecanoidince (except Oceanodroma) are remarkable, but in this 

 case the majority possess long legs, and Phoebetria a long tail. 

 Most remarkable of all is, I think, the entire absence of a forked 

 tail amongst groups such as the Accipitrince and Falconince, in 

 which the powers of flight have been so strongly developed. 



