523 
1921 .] Bird-Migration by the Marking Method. 
“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. If 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-sseking 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. 
