MIGRATION OF BIRDS 
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take part in the migratory movement at any time cannot be 
proved. It is quite possible that when our knowledge of the 
nesting-habits of the birds of this country is increased, it will 
be found that quite a number of European birds remain to 
breed in some part of Africa. Thus, who can say whether the 
Great Spotted Cuckoo, which is found breeding in South and 
East Africa, was at one time purely a winter visitor to these 
countries and not a resident breeding species ? (See examples, 
adults and young.) Has the bird extended its breeding range, 
and will the African birds in time become a distinct form ? 
Evidence seems to point this way. 
Manner of Migrating . — The manner of migrating is interest- 
ing. Some species migrate in flocks of their own species ; others 
in mixed flocks ; others, again, travel alone. These three 
methods are of importance when considering the governing 
factors regarding routes. 
How do the birds know the correct route ? What guides 
them ? According to certain observers, each species has its 
definite route or routes ; but the routes of certain species may 
coincide for part of the way or for the whole distance. Our 
knowledge on these points is small ; thus we find authorities 
disagreeing. 
Manner of Travelling . — It seems to be established that all 
the birds of a given species and from a given locality do not 
migrate together and at the one time ; thus we find the move- 
ment to be wave-like ; one batch of birds starting the movement, 
to be followed at varying interval of days by fresh batches. 
In certain species the young birds are the first to arrive ; in 
others, again, the adults ; then when we consider the return or 
spring movement, we find that with certain species the males 
travel by themselves and the females by themselves, and in 
many of these cases the males arrive at their destination first. 
Not only do we find this to be the case with some European 
birds, but we see it also with certain of the Weaver Birds in this 
country. The males arrive at a nesting-site and begin to weave 
their nests : the females turn up later and help to finish the work. 
Directive Agents . — Several suggestions have been put for- 
ward ; keenness of vision and recognition of landmarks, high 
development of sense of direction and locality, and knowledge 
