KILBUCK AND AHKLUN MOUNTAIN BIRDS 



151 



Possibly, the two species most exemplifying the phenomenon of a 

 boundary or overlap between close congeners were dowitchers; the 

 long-billed dowitcher nests primarily to the north and west, and the 

 short-billed dowitcher nests primarily to the south, but both species 

 probably nested on our study area near Goodnews Bay. Although further 

 investigation is needed, the range of sympatric species or subspecies 

 pairs nesting in our area is striking. Several of the species or species pairs 

 that were sympatric in the area were Old World and New World forms; 

 that is, a goshawk, possibly Siberian, bred with an American goshawk. 

 The lesser (Pluvialis dominica) and Pacific golden-plovers (P.fulva) are 

 sympatric in western Alaska (Connors 1983); however, too few golden- 

 plovers were collected in our area to document both species as nesting. 

 Adult herring gulls on the west coast of our area were dark-mantled, 

 whereas DNW saw light-mantled adults just north of our area at Aniak 

 (village) in 1986, and just east of it at Dillingham in 1962. This suggested 

 that Siberian Lams argentatus vegae occurred on the west coast, while 

 American Z. a. smithsonianus more or less reached the northern interior 

 and southern coast. 



Our study area is in the western Alaska biogeographic region of 

 Kessel and Gibson (1978), but elements of the avifaunas of western 

 Alaska, southwestern Alaska, southcoastal Alaska, and central Alaska are 

 present. The taiga-tundra transitional nature of our avifauna, and the 

 presence of both Beringian and Old World breeding forms fit Kessel and 

 Gibson's (1978) concept of a western Alaska avifauna. However, the 

 breeding waterfowl, seabirds, and shorebirds of our area include a 

 number of species considered part of the southwestern, southcoastal, 

 and southcoastal island avifaunas (c.f. Gabrielson and Lincoln 1959; 

 Kessel and Gibson 1978). Many species and subspecies reach the south- 

 eastern and northwestern or western limit of their breeding or presumed 

 breeding range in the study area. 



We therefore conclude that the southern part of our area marks an 

 avifaunal as well as physical limit between Bristol Bay and Kuskokwim 

 Bay. We suggest that the western slope of the Kilbuck and Ahklun 

 mountains is best regarded as part of the western Alaska biogeographic 

 region and that the area from Cape Newenham east to the Togiak River 

 is part of the southwestern Alaska biogeographic region. 



