1370 U.S. NATIONAL MUSEUM BULLETIN 23 7 part 3 



Although a canopy of dead bracken was a feature of many nests, 

 in no case was the nest begun under an overstory of live mature 

 bracken. At the time when many early nests were found, however, 

 young growing bracken fronds were evident. As the season progressed 

 and this bracken matured, new nests were restricted to patches of 

 blueberry that did not contain bracken. Thus these later nests had 

 no canopies of dead bracken. 



Four characteristics of the larger vegetation within a 50-foot radius 

 of the nest sites were notable. First, there was usually one large 

 object or group of objects, a tree, shrub, stump, or log, close to each 

 nest, and a positive correlation between the height of this object 

 and its distance from the nest. In other words, the nest is positioned 

 on the ground at a definite angle from the top of the nearest large 

 object, which may provide a lookout point for the bird before it flies 

 down to the nest. 



The other three characteristics refer to the amount of cover afforded 

 by the objects about the nest site, and the number of feet of edge 

 around them. To measure those, a circle of 50-foot radius centered 

 about the nest was divided into five annular rings, each 10 feet wide. 

 The percent of cover, the number of feet of edge per square foot of 

 total area, and the number of feet of edge per square foot of cover 

 were measured separately for each of the five concentric areas. 

 Measurements within a 10-foot radius about random points were 

 made to show conditions in the general habitat for comparison with 

 nest sites. Comparisons were also made between these same charac- 

 teristics surrounding the nest sites of white-throats, song sparrows, 

 and slate-colored j uncos, all of which nested in the same general area. 



The data showed that the average amount of cover within the 

 10-foot radius about sites of white-throat nests is similar to that 

 within the general habitat in which the species nests, but the variation 

 in the cover values about the nest sites is much less than that within 

 the rest of the habitat. Also, the values for sites is intermediate 

 between values for the open sites of song sparrow nests and the dense 

 sites of slate-colored junco nests. 



The amount of edge about objects within the 10-foot radius of 

 nest sites of white-throats is significantly greater than the amounts 

 of edge in the general nesting habitat of this species. Furthermore, 

 it was found to be greater than that about sites of song sparrow and 

 slate-colored junco nests. 



Finally, measurements of the number of feet of edge per unit area 

 of cover (which is a measure of the dispersion or arrangement of 

 objects) showed that although the dispersion of objects within the 

 10-foot radius did not differ from the average dispersion in the rest 

 of the nesting habitat, there was much less variation than that existing 



