Foraging Relationships of Brown‐Headed Nuthatches and Pine Warblers

Foraging behavior and interactions between Brown—headed Nuthatches (Sitta pusilla) and Pine Warblers (Dendroica pinus) were studied in longleaf pine lands of Louisiana during the fall and winter of 1963—64 and 1964—65. Both species frequently were members of flocks that formed around Carolina Chickadees (Parus carolinensis) and Tufted Titmice (P. bicolor). Most contact between the former two species occurred in these flocks. While in flocks, Brown—headed Nuthatches foraged most heavily on the distal parts of limbs and on twigs, Pine Warblers on proximal parts of limbs. When alone, Brown—headed Nuthatches foraged more heavily on trunks and proximal parts of limbs than they did when Pine Warblers. When pine seeds were abundant, Brown—headed Nuthatches fed upon them heavily and regularly ventured to large limbs and trunks to crack seeds, causing increased hostilities with Pine Warblers. Attempts to crack seeds where bark was not sufficiently rough to permit adequate anchoring met with little success. Pine Warblers fed upon pine seeds much less frequently than did Brown—headed Nuthatches. During the height of seed abundance, Brown—headed Nuthatches lingered behind mixed flocks and often became separated from them. More competition for food apparently exists between Brown—headed Nuthatches and Pine Warblers than between either of these species and others. The noticeably different foraging distribution of the two species when together and apart is probably largely the result of the presence or absence of the other. Dividing the habitat in each other's presence avoids fighting over a similar foraging station. Abundant food sources may cause this system to break down.