MIGRATION—-MEINERTZHAGEN. 345 
the first of these conditions Sztta canadensis, occurring in Corsica, 
China, and America; Cyanopica cyanus, in Spain and Eastern Asia ; 
and Pyrrhocoraxz pyrrhocorax, with its reported isolated colony in 
Abyssinia, afford good examples. 
Tsolation will in its turn most assuredly produce differentiation. 
In these three above-quoted cases there can be little doubt that the 
isolated colonies emanated from the same parental stock and that 
they primarily emigrated from the same area. As in Mesopotamia, 
we find derelict remains of ancient civilization, such as the banks of 
some Babylonian canal, cropping up at sometimes great intervals, 
and only giving us a general clue to a once huge work, so we find 
among some species derelict groups or forms cropping up in widely 
separated parts of the world as landmarks of some bygone migra- 
tion or continuous distribution. 
Such gradual movements as are outlined above, when undertaken 
by what are commonly believed to be resident species, represent in 
fact incipient migration or movements from which a strong migra- 
tory habit has since developed in other species. 
2. PERIODIC AND REGULAR MIGRATION. 
We see periodic and regular migration effecting changes in breed- 
ing-area in certain species of Palaearctic birds. We find the bee 
eater (Merops apiaster) taking advantage of South African condi- 
tions and establishing breeding colonies there. (Stark and Sclater, 
Fauna of South Africa, Birds, iii, p. 59.) That this species breeds 
regularly in Algeria and Egypt is beyond question, and it seems pos- 
sible that it also breeds in the northern Sahara. (Novit. Zool., xviii, 
1911, p. 524, xx, 1913, p. 60.) It is not then surprising to find them 
nesting in South Africa, where conditions are more favorable than 
in north Africa. But it is not inferred that this bird breeds twice a 
year, once in its normal summer haunts and again in its winter 
haunts. It is more likely that the colonies which breed in South 
Africa are resident communities who have dropped the migratory 
habit as redundant to their life. 
Again, we find the sandpiper (Yotanus hypoleucus) nesting in 
tropical East Africa (Van Sommeren), and the writer observed the 
young of this species with their parents on the Kajiado River near 
Nairobi in 1915. The pratincole is reported to have bred in a colony 
near Durban in November, 1917 (Ibis, 1908, p. 385), Geoffroy’s sand 
plover is suspected of breeding in Somaliland (Archer), and the 
swallow (Hirundo r. rustica) in Uganda and on Kilimanjaro. 
It is held that these cases of expansion of the breeding range are 
directly attributable to migration, as they all occur among species in 
which the migratory instinct is strongly developed. Whether or no 
