DISPERSAL AND MIGRATIONS 165 



apparatus for aerial movement ; those that fly 

 least the weakest ; and in some cases, as we 

 have already seen, disuse of the wings has 

 eventually ended in loss of flight altogether. 

 It is not a necessary corollary, however, that 

 all long -winged birds are migrants. Many 

 sedentary birds have long wings, but this is the 

 result of having constantly to depend upon 

 them to secure food : the Humming-Birds and 

 many Birds of Prey are cases in point. It is 

 most significant that the groups with the most 

 rounded and concave wings are generally dwel- 

 lers in w^arm regions, leading a sedentary life ; 

 in cold and temperate regions it is the excep- 

 tion to find a short weak-winged bird, the rule 

 for them to have long and strong ones. Again, 

 in order that migratory birds may be best able 

 to undertake their periodical journeys, we find 

 that they generally moult their plumage before 

 they start. Once this tedious and dangerous 

 process is over, migrating birds, which during 

 its progress were sickly and skulking, brighten 

 up, and each day only seems to increase the 

 impulse to commence their annual passage. 

 But migrants, as most observers know, do not 

 all start off together ; the ones that complete 

 their moult earliest seem in many cases to be 



