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Wooded Islands in a Sea of Prairie

Results and Discussion

Fort-seven bird species in the 30 wooded draws censused for breeding were recorded. An additional 23 species were found occupying adjacent draws or habitats in proximity to wooded draws. These figures indicate that at least 23% of the known nesting avifauna of North Dakota was found in the wooded draws censused, and nearly 34% of the total was found occupying wooded draws or adjacent habitats (Faanes and Stewart 1982). The mean number of bird species recorded per draw was 13.2, with the range 8-18 species. The most frequently occurring species were Rufous-sided Towhee, Brown-headed Cowbird, House Wren, and American Goldfinch (Table 2).

Among families, the Emberizidae accounted for 42.6% of all species recorded in wooded draws, and 42.2% of all bird species recorded in all habitats studied in 1982 (Table 3). Within the Emberizidae, 8 species were grosbeaks, 7 were warblers, and 5 were blackbirds. The Tyrannidae were second most numerous, making up 12.8% of the wooded draw bird species and 8.4% of all species recorded.

Each of the 30 census plots were within 11 subareas. For this analysis, I grouped the plots into 10 subareas, leaving out the lone plot in the Garrison Dam Quadrangle. These data suggest that the Cussicks Spring area of Williams County and the Zap area of Mercer County supported the highest mean breeding densities (Table 4).

Among all subareas, the lowest mean breeding-bird density and two of the three lowest mean species-richness values were from wooded draws either adjacent to the Missouri River or along the floodplain of the Knife River. Wooded draws along the Knife River generally supported high ground-cover values, low shrub density, and fewer individual large trees. Because these draws were located along the floodplain of a moderately large stream, the low shrub layer is subjected to increased frequency and duration of floods which may hinder the colonization of this layer by low-ground-layer breeding bird species. Examination of the species lists for these three draws revealed that among the 16 bird species recorded, only three (19%) are typical of ground or shrub layer vegetation.

Among the 34 breeding bird species that reached maximum numbers in individual draws or subareas, 18 or 53% occupied the three western subareas (Table 4). Three of the eastern subareas (Ft. Clark, Stanton, Medicine Butte) supported four species (12%) among them that reached maximum numbers, and of these the Stanton subarea was the only one not to support maximum numbers of at least one bird species.

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