Effects of group size and group density on tradeāoffs in resource selection by a groupāterritorial centralāplace foraging woodpecker
Tradeāoffs in resource selection by centralāplace foragers are driven by the need to balance the benefits of selecting resources against the costs of travel from the central place. For groupāterritorial centralāplace foraging birds, tradeāoffs in resource selection are likely to be complicated by a competitive advantage for larger groups at high group density that may limit accessibility of highāquality distant resources to small groups. We used the groupāterritorial, centralāplace foraging Redācockaded Woodpecker Leuconotopicus borealis (RCW) as a case study to test predictions that increases in group density lead to differences in foraging distances and resource selection for groups of different sizes. We used GPS tracking and LiDARāderived habitat data to model effects of group size on foraging distances and selection for highāquality pines (≥ 35.6 cm diameter at breast height (dbh)) and lower quality pines (25.4–35.6 cm dbh) by RCW groups across low (n = 14), moderate (n = 10) and high group density (n = 10) conditions. At low and moderate group density, all RCW groups selected distant highāquality pines in addition to those near the central place because competition for resources was low. In contrast, at high group density, larger groups travelled further to select highāquality pines, whereas smaller groups selected highāquality pines only when they were close to the central place and, conversely, were more likely to select lower quality pines at greater distances from the central place. Selection for highāquality pines only when close to the cavity tree cluster at high group density is important to longāterm fitness of small RCW groups because it allows them to maximize benefits from both territorial defence and selecting highāquality resources while minimizing costs of competition. These relationships suggest that intraspecific competition at high group density entails substantive costs to smaller groups of territorial centralāplace foragers by limiting accessibility of distant highāquality foraging resources.