1 92 1.] Bird-Migration hy the Marking Method. 523 



^'Individual Migration.'''' — This term is used to express the 

 fact that individual birds belonging to the same species and 

 native to the same area may behave differently as regards 

 migration. The point has been very clearly brought out 

 by the marking method, and in the preceding sections 

 numerous instances are given where individuals have sought 

 different winter-quarters, or where some individuals have 

 remained sedentary, while others have migrated. In the 

 case of Lapwings bred in Aberdeenshire and the neigh- 

 bouring counties, for example, some have wintered there, 

 some in Ireland, and some in Portugal. Theoretically, the 

 question seems to present two alternatives. I£ all the birds 

 are naturally endowed with a similar instinct, what is it 

 that stimulates this to greater activity in some cases than 

 in others where the general conditions are apparently the 

 same ? And if different instincts, or degrees of instinct, are 

 inherited, how may this be accounted for — are there different 

 gentes not morphologically distinguishable, but differing in 

 constitution and temperament in ways not at present definable, 

 as, for instance, a sedentary gens, an Ireland-seeking gens, 

 and a Portugal-seeking gens ? (Or, as a very unpromising 

 alternative, must we re-examine the apparently overwhelming 

 evidence in favour of migration being an inborn-habit rather 

 than a direct effect of immediate stimuli ?) 



Types of Migration. — An interesting point has been brought 

 out in the case of several species, namely, the absence of 

 records of marked birds from what may be called " inter- 

 mediate distances," a bird being usually recorded either from 

 its native locality or from a comparatively great distance. 

 In these cases it accordingly seems probable that individual 

 birds are either quite sedentary or very definitely migratory, 

 gradations being absent. In other instances, such as that 

 of the Herring-Gull, the records clearly reveal a rather 

 indefinite wandering tendency. 



Sedentary Birds. — Some interest attaches to the evidence 

 of the extreme nature of the sedentary habit of many 

 individual birds, these being often recorded time after time, 

 over a period of years, from the very same gardens. 



