Restoring a pine in decline: Foraging ecology of Clark's nutcracker and red squirrel in whitebark pine forests

Background/Question/Methods

Whitebark pine (Pinus albicaulis), a keystone species of high elevation ecosystems in western North America, is in decline throughout its range. Clark’s nutcracker (Nucifraga columbiana), a bird that collects and stores whitebark pine seeds in ground caches, is the primary seed disperser of whitebark pine. Nutcrackers compete for whitebark pine cone resources with red squirrels (Tamiasciurus hudsonicus), a major whitebark pine seed predator. Whitebark pine restoration efforts must take into account the complex ecology of Clark’s nutcracker and red squirrel foraging habits in whitebark pine stands. In this study, we monitored and quantified Clark’s nutcracker and red squirrel foraging on whitebark pine cones in Glacier National Park, Montana. We also collected data on physical and compositional characteristics of the sites, whitebark pine cone production, and whitebark pine health. We completed a correlation analysis to examine the relationships between these factors and determine which characteristics define the sites where nutcrackers and squirrels forage most successfully. 

Results/Conclusions

Nutcrackers harvested seeds from a greater proportion of cones in the stands where they started foraging earlier (R = -0.985, p = 0.02). Nutcrackers began harvesting earlier in areas where whitebark pine was relatively more abundant (R = -0.961, p = 0.04). In addition, squirrels depleted the cone source more quickly in stands where a greater proportion of whitebark pine trees were dead (R = 0.977, p = 0.004). Because nutcrackers harvested more seeds in stands where they started foraging earlier, restoration efforts, such as whitebark pine seedling planting, should occur in sites where whitebark pine is more prevalent. It is also important to focus on those areas because, as the results suggest, squirrel populations are not vulnerable to the decline in whitebark pine and will deplete the remaining cone source more rapidly as the trees continue to die. However, if healthy trees remain abundant in these stands, nutcrackers will have access to cones without increased competition from squirrels.