16 BIRDS OF THE NEW YORK CITY REGION 



most of the species concerned, the cause is obviously the 

 interference of man. The disappearance of the Acadian 

 Flycatcher however, cannot be ascribed wholly to this cause. 

 If Giraud's statements, written in 1842, can be credited, the 

 decrease of Carolinian species has been going on ever since 

 then. The Red-bellied Woodpecker, which is now of acciden- 

 tal occurrence, was formerly a permanent resident on Long 

 Island. I cite this, one of several southern species which have 

 completely disappeared from our region, because the inter- 

 ference of man cannot reasonably be advanced to explain it. 

 Unfortunately the accurate and detailed data of the present 

 did not exist in the past, and this interesting question can 

 never be settled definitely. 



II. The Alleghanian or Transition Zone. It can readily 

 be inferred from the foregoing, that the southern limit of this 

 Zone is approximately reached in this region. The following 

 species, at sea-level, reach their southern breeding limit here 

 or but little south of us : 



Carolina Rail Rose-breasted Grosbeak 



Alder Flycatcher Purple Finch 



Least Flycatcher Golden-winged Warbler 



Bobolink Chestnut-sided Warbler 



Savannah Sparrow Black-throated Green Warbler 



Wilson's Thrush 



As with the Carolinian birds, there is much still to be 

 learned of the factors limiting the southward extension of these 

 species. The majority, however, are rare or absent on the 

 coastal plain of Long Island and Staten Island, which is a 

 more definite statement than is possible for the northern 

 limits of the Carolinian species. Most of them also increase 

 northward, as might be expected, but the Purple Finch and 

 Savannah Sparrow do not, for which there is no available 

 explanation. The Black-throated Green Warbler is very 

 irregularly distributed, and turns up in three distinct habitats, 

 with different associations of species and radically different 



