Use of Conifers by Red Squirrels (Tamiasciurus hudsonicus) in Montana For Drying and Caching Mushrooms

Abstract

The diet of Red Squirrels (Tamiasciurus hudsonicus) is composed primarily of tree seeds, but may include: tree buds, flowers, bark, sap, fruits, insects, bird eggs, nestlings and adults, and other vertebrate flesh (Steele 1998), depending on circumstance and opportunity. Epigeous and hypogeous fungi are also important foods for Red Squirrels in some areas, particularly during autumn and winter (CC Smith 1968; Ferron and others 1986; Currah and others 2000). At least 89 species of fungi have been reported in their diet (Fogel and Trappe 1978), making Red Squirrels important dispersers of fungal spores (Laursen and others 2003). During the harvest of conifer cones and creation of cone caches, Red Squirrels may also collect fruiting bodies (sporocarps) of mushrooms and deposit them in trees for drying, caching, and later consumption. This behavior has been widely reported in the literature (Seton 1909; Buller 1920; Cram 1924; Murie 1927; Hardy 1949; CC Smith 1968; Gurnell 1984; Vernes and Poirier 2007), including popular field guides (for example Murie 1954), but remains little studied. Thus, few details have been published about the density of cache trees in individual squirrel territories, number of mushrooms per cache tree, relative abundance of different mushrooms in cache trees, or the relative use of different tree species for caching. On 4 November 2014, in Pattee Canyon, Missoula County, Montana (46.815466N, 113. 916156W; 1433 m elevation), we encountered 2 Western Larch (Larix occidentalis) trees with mushrooms cached on their lateral branches. The 1st larch (about 8 m tall and 13 cm dbh) supported 8 mushroom stems and caps between 0.25 and 1.0 m from the trunk and 1.0 to 3.5 m above ground. The 2nd larch, of equal size as the first, had 2 mushrooms supported on branches 2.0 and 3.0 m above ground. Lowest branches on both larches were 0.25 m above ground, and both were mostly devoid of needles by this time. The site was north-facing within an old seed-tree cut now dominated by a mixed stand of young Western Larch, Douglas-fir (Pseudotsuga menziesii) and Ponderosa Pine (Pinus ponderosa), with a shrub layer including alder (Alnus sp.), Saskatoon Serviceberry (Amelanchier alnifolia), Mallow-leaf Ninebark (Physocarpus malvaceus), and Rocky Mountain Maple (Acer glabrum). We revisited the site on 6 November to photograph the mushrooms for later identification and determine if any had been removed from the original 2 trees. The 1st larch now had 5 mushrooms instead of 8; the 2nd still had the original 2. Although we did not see a Red Squirrel harvesting or carrying mushrooms to or from the trees on these or later visits, a squirrel was present each time within 15 m of the mushroom trees, and tooth marks of a size typical for Red Squirrels (based on examination of skulls in the Philip L Wright Zoological Museum) were present in all cached mushrooms we examined. We visited the site a 3rd time on 8 November to obtain a count of trees in the immediate area that were used to dry and cache mushrooms. The 5 mushrooms present in the 1st larch on 6 November were still there, the 2nd larch now had none. We inspected all trees of pole-sapling size or larger within a rectangular area roughly 625 m (25 m 3 25 m, centered on where we had seen a Red Squirrel near the original mushroom trees on the first visit) to determine how many held cached mushrooms. Ten of 35 larch and 1 of 26 Douglas-fir held at least 1 mushroom on 1 of our visits; the difference in conifer species used for caching mushrooms was statistically significant (x with Yates correction 5 4.61, P 5 0.032). For this sample, 8 trees had single mushrooms, 1 had 2, 1 had 4, and 1 had 8. Mushrooms were wedged on branches 1.0 to 6.0 m above ground (mean 5 2.8 m, s 5 1.6 m), GENERAL NOTES