Proceedings of the British Association t, 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 w-ater birds. Several of the 

 generic forms were peculiar, but only two of the families, viz. the 

 Trochilida3 and Psittacidse, were not to be found in Europe j 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 Corvidae 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- 

 dae are European. The number of species common to North and 

 South America is very uncertain. 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 conv^enient 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 



