12 PROCEEDINGS OF THE 



Thrushes, which were so abundant at Tamarack, became scarce, 

 while Wood Thrushes and Wilson's became rather more 

 abundant. We looked carefully for Hermit Thrushes, but not 

 a single one was heard or seen. Neither were any Brown 

 Creepers met with. In the latter case, however, their presence 

 might easily have escaped our notice, as in no instance did we 

 have time to push back into the forest more than a mile from 

 the road. 



Enough has been said, I think, to show pretty clearly the 

 close relationship between the geographical distribution of the 

 summer birds belonging to the Canadian fauna and the original 

 primeval forests which once covered the mountains of Pennsyl- 

 vania. Where those forests still exist in large tracts, as, for 

 example, they did a few years ago on North Mountain, there we 

 find a very strong, if not a predominating, tinge of the Canadian 

 fauna. On the other hand, where they have been entirely de- 

 stroyed or broken vip into isolated patches, those birds which 

 may be regarded as typical of the Alleghanian fauna are in the 

 majority. In the latter case, even where the altitude is above 

 1,200 ft., certain Carolinian species are beginning to find their 

 way north. Such at least is the only good explanation which 

 we can offer for the presence in recent years of the Chat in a 

 mountain region where it was never before known. [See below.] 



In the case of the forest regions of Potter and Clinton coun- 

 ties, with which the present paper deals, I am inclined to think 

 that the fauna is rapidly changing from Canadian to Alle- 

 ghanian, with a tinge of the Carolinian. To be sure, most of 

 the birds noted at Tamarack Swamp must be regarded as be- 

 longing to the former (i. e.. Canadian), but there the whole 

 environment is pecuUarly suited to their habits. In the south- 

 ern part — indeed, throughout the whole of Potter county — we 

 find an interesting transition going on. The large bodies of un- 

 cut timber which still exist in the Upper Kettle Creek Valley 

 can no longer be regarded as typical of the conditions prevailing 

 throughout the entire county; rather, they are exceptions to the 

 general rule. As such their fauna naturally contains a large 

 percentage of northern species, yet it is already becoming more 

 southern in its character. What will be the fate of manv of 



