Ecological Distribution of Birds in the Napaskiak Area of the Kuskokwim River Delta, Alaska

Abstract

Few critical studies of the distribution of birds in Alaska have been made which are directed toward the accumulation of data on the effects of biotic and physical factors in controlling species occurrence. In this region, as in others at northern latitudes, the number of vegetational formations of a rank sufficient to influence the distribution of birds is relatively limited. Superimposed on this is a climate that is rigorous in many aspects. In such a region, it seems likely that field studies will be helpful in ascertaining the relative significance of biotic and physical factors in limiting abundance and providing barriers to distribution of birds. Recent studies of avian distribution have revealed the importance of some aspects of the biotic environment. Pitelka (1941) emphasized the importance of biotic interrelations, especially responses to the physiognomy of vegetation, as controlling factors in the distribution of birds. Miller (1951) has demonstrated, in California, that climatic extremes usually do not affect the distribuitional pattern of a species when a suitable plant formation is present; the effects of climate are reflected, in an indirect way, by the ability of the plants to withstand the extremes. Local studies of bird distribution provide basic data from which an understanding of the relative role of biotic and climatic factors may be developed, and it is toward this end that this paper on the avifauna of a poorly known sector of southwestern Alaska has been prepared. Sufficient data have not yet been gathered to ascertain the importance of climate on the distribution of birds in the area under consideration, along the Kuskokwim River, but it is suspected that the direct action of climatic or other physical factors may be significant in a few instances. The Napaskiak area, approximately 40 square miles in extent, is situated in the upper portion of the Kuskokwim River delta and includes the land adjacent to the south shore of the river as well as islands in the river itself. Its center is in the Eskimo village of Napaskiak about eight miles southwest of Bethel (fig. 1). The area is of particular biological interest because it lies along the western terminus of the vast, interior spruce forest where this plant community interdigitates with the broad, flat, coastal plain or tundra of the Yukon-Kuskokwim delta (fig. 2). Characterizing this overlap of markedly different vegetation types is an avifauna consisting of elements derived from each major community, along with those species common to both. The Napaskiak area was visited by Robert Rausch and the writer during late May and early June of 1955. Return trips were made by the writer in August of the same year and again in May and June of 1956. The writer spent a total of 37 days in the area. The primary purpose of this work was the investigation of animal-borne diseases, an activity affording ample opportunity to obtain a fairly extensive and representative collection of birds. These specimens, in conjunction with field notes and photographs made in the area, constitute the basis for this report.