Clark’s Nutcrackers (Nucifraga columbiana) caching Whitebark Pine (Pinus albicaulis) seeds in trees

Abstract

On 17 September 2017, I observed two Clark’s Nutcrackers (Nucifraga columbiana) from 8–10 m distance as they cached seeds in a stand of dead Whitebark Pines (Pinus albicaulis) at 2500 m elevation on Saint Mary Peak in the Bitterroot Mountains of Ravalli County, Montana. Over 5 minutes, the nutcrackers created 14 caches in seven different multi-trunk tree clusters in an area of about 50 m2. All caches appeared to be single Whitebark Pine seeds, positioned 2–5 m (mostly 3–4 m) above ground in dead trees. Of the 14 caches, three were placed under loose pieces of bark on a trunk (one) or large limb (two), and the remaining 11 were in encrustations of American Wolf Lichen (Letharia columbiana) growing on branches of the dead trees. Nutcrackers are known to sometimes cache seeds above ground in trees during the late summer and autumn harvest of pine seeds, but usually not to the exclusion of other microsites. The ground at the Montana site was covered by 7–9 cm of fresh snow that fell the previous day, which may have encouraged the nutcrackers to place all of their seed caches above ground in trees.