Proceedings of the British Association. 377 
Species are common to Asia also.—The report then proceeded with 
an account of the Ornithology, which Dr. Richardson said it would 
be unnecessary to touch upon at so great length or with so much 
detail as the Mammalia, since the species were so much better known, 
a great majority of them being migratory, and therefore those which 
lived in the less frequented regions were, at stated seasons, visitants 
of the more civilized districts. Local lists, however, were still want- 
ing to enable naturalists to trace their geographical limits with pre- 
cision, and, more especially, our knowledge was very imperfect of 
those of California and Russian America. Of about five hundred 
species, there were one fourth to be found in Europe, but not more 
than one eighth in South America. Of the former, or those com- 
mon to North America and Europe, thirty nine were land birds, 
twenty eight waders, and sixty two water birds. Several of the 
generic forms were peculiar, but only two of the families, viz. the 
Trochilide and Psittacide, were not to be found in Europe; and the 
Hoopoe is the only European representative of the whole order to 
which the former of these families belongs. No vultures are com- 
mon to both worlds, but nearly half the other birds of prey are so, 
and many of these range over South America also, and indeed the 
whole world. One fourth of the Corvide are inhabitants of Europe; 
but the other land birds, common to both continents, are in much 
smaller proportions, and not more than two out of sixty two Sylvia- 
e are European. The number of species common to North and 
South America is very uacertain. Some of the most numerous fami- 
lies characteristic of the former country have few or no species in 
South America. It is remarkable that only one Trochilus has been 
described as common to North and South America, although this 
family is peculiarly characteristic of the latter country ; and there 
are twenty two species which have been described as natives of 
Mexico. Dr. Richardson then detailed several particulars respect- 
ing the migration of birds, stating it to be his opinion, that the spring 
movement was for the purpose of finding a convenient place for in- 
cubation and rearing the young. The lines of route were influenced 
by the supply of food to be obtained, and thus the northerly and 
southerly courses were often over different tracts; and he pointed 
out the three great lines of route which were to a certain extent 
determined by the physical features of the country. The absolute 
number of birds to be found in different countries decreases on re- 
ceding from the equator towards the north pole; but of those which 
VoL. XXXI.—No. 2. 48 
