266 On the Physical and Geographical Distribution 



with the great extent of bog throughout the island, brings 

 hither to winter different species of grallatorial and other 

 birds, in much greater numbers than prevail in England or 

 Scotland. The extent of moist and rich meadows in sum- 

 mer, has a similar but more limited influence. The want of 

 extensive districts of old timber seems, when fully considered, 

 to have little effect in excluding from Ireland species which 

 inhabit Great Britain. 



To the laws o^ geographical distribution alone must, I con- 

 ceive, be attributed our want of species not affected by any 

 of the foregoing causes, — viz., physical geography, minera- 

 logical structure, climate, and absence of old timber. It should 

 be borne in mind, that in all the preceding remarks, the mere 

 absence or presence of species is considered ; consequently, 

 nothing is said of birds, from different causes, being less fre- 

 quently met with in Ireland than in particular parts of Eng- 

 land or Scotland. Such points will be fully treated of under 

 the respective species. 



Although, in their polar and equatorial migrations, the 

 crossing of a sea, — as the Mediterranean for instance, — offers 

 no obstacle to birds, yet is it different when they are spread- 

 ing latitudinally, either to the east or to the west, in which 

 ease the migration of many species terminates at the mar- 

 gin of the sea. Were Ireland, therefore, geographically 

 joined to Great Britain, some species that are not now found 

 would certainly inhabit it, but the junction would make no 

 difference with respect to others, — resident as well as migra- 

 tory birds. In that event we should, in the east of Ireland 

 at least, have those species which are found throughout the 

 most western portion of Great Britain, in the same parallel 

 of latitude ; but not those whose range of distribution does 

 not extend to the most western counties of England and to 

 Wales. The species which Ireland would and would not 

 have, under such circumstances, may be inferred from an ex- 

 amination of the summary appended to the end of each order 

 of birds, where the distribution over Great Britain, of the 

 species not known as Irish, is pointed out. We should, for 

 example, if the country united them, have, as resident birds, 

 the green woodpecker and the nuthatch ; of annual summer 



