CLARK’S NUTCRACKER SEED USE AND LIMBER PINE METAPOPULATION STRUCTURE IN ROCKY MOUNTAIN NATIONAL PARK

Williams, Tyler

The Clark’s nutcracker (Nucifraga columbiana) is the major seed disperser for limber pine (Pinus flexilis), which in turn is a preferred conifer food source for the nutcrackers. Limber pine exhibits a metapopulation structure: regional populations consist of small, local populations connected by seed dispersal. Current and predicted threats to limber pine include mountain pine beetle (Dendroctonus ponderosae) outbreaks, larger wildfires, and especially exotic white pine blister rust (pathogen Cronartium ribicola). Extensive limber pine mortality may force nutcrackers to rely on alternative conifer seed sources. In Rocky Mountain National Park (RMNP), I investigated the importance of alternative seed sources for nutcrackers, limber pine’s metapopulation structure, and how local population connectivity might be influenced by nutcracker spatial use. From mid-June to late October 2014 to 2016, data were collected on: 1) cone production in stands of limber pine, ponderosa pine (Pinus ponderosa), and Douglas-fir (Pseudotsuga menziesii); 2) timing of nutcracker stand visitation; and, 3) nutcracker seed harvest and caching behavior; 4) limber pine geographic occurrence within RMNP using GIS layers; and 5) radio-tracked locations for nutcrackers in 2015-2016. Limber pine component populations (n = 51) ranged from 1 - 400 ha in size with inter-population distances of 1 - 36 km. Nutcrackers traveled distances ranging from 1 - 12 km (n = 7 nutcrackers) and cached seeds 2.2 km away from the foraging site (n = 1 iv nutcracker), indicating potentially high limber pine metapopulation connectivity, even with a smaller nutcracker population. Annual variation in cone production influenced nutcracker foraging preferences and the use of different seed sources. Each year starting in mid to late August, nutcrackers foraged on limber pine seeds, which ripen in early September. In 2014 and 2015, nutcrackers transitioned to harvesting ponderosa pine seeds, which ripen in early October. In 2016, instead they transitioned to Douglas-fir seeds, which ripen in late September. With potential limber pine losses, I believe that alternative seed sources will support a nutcracker population, although carrying capacity may be lower. I suggest that ponderosa pine will serve as an increasingly critical food resource if limber pine declines.