Irish Ornithology . 401 



The Firecvest (Regulusignicapillus), the Bearded Tit (Panurus 

 biarmicus), and the Crested Tit (Parus cristatus) , are so very 

 local in England and Scotland that their absence from Ireland 

 is not very surprising ; but that the Marsh Tit (Parus pa- 

 lustris) should be very rare in the north and east of Ireland, 

 and not be known at all in the south and west, and that the 

 Nuthatch (Sitta ccesia) should be absolutely unknown in 

 Ireland, is most extraordinary. Both the last-mentioned 

 species belong to circumpolar genera, one might even say 

 circumpolar subgenera, both are found with very slight modi- 

 fications all across the Paleearctic Region to Japan, and both 

 are represented by closely allied species in the Nearctic Region. 

 That such widely spread species should be absent, or nearly 

 so, from Ireland is a most significant fact. Ireland is most 

 admirably adapted for woodland birds of this kind, and their 

 absence can only be accounted for by the hypothesis that some 

 great catastrophe, such as a glacial epoch, drove them from 

 the island, and that they have not yet found their way back 

 again. The Marsh Tit and the Nuthatch are both as common 

 in Northern Europe up to the Arctic Circle as they are in 

 England, but curiously enough they are almost as rare in 

 Scotland as they are in Ireland. These and many other 

 species to be hereafter mentioned have evidently migrated to 

 the east of England from the continent, whence they have 

 slowly extended their range northwards to Scotland, whence, 

 at a still later date, they have migrated southwards across 

 the North Channel into Ireland. If these hypotheses be 

 true, the following facts ought to be observable :— Firstly, we 

 should expect to find that species which are common in Eng- 

 land, but are absent or rare in Ireland, are also absent or 

 rare in Scotland. Secondly, we should expect to find that 

 species which have advanced a stage further in the extension 

 of their range and have reached Scotland in some numbers, 

 but are still rare or local in Ireland, are most abundant in 

 the north-west of that country, in those districts which lie 

 nearest to Scotland. Most of our information respecting the 

 distribution of birds in Ireland supports both these assump- 

 tions in a remarkable manner. The Nuthatch is so rare in 



