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Use of a Robin’s Nest as a Cache Site for Truffles by a Red Squirrel
Karl Vernes and Nelson Poirier

Northeastern Naturalist, Volume 14, Issue 1 (2007): 145–149

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2007 NORTHEASTERN NATURALIST 14(1):145–149 Use of a Robin’s Nest as a Cache Site for Truffles by a Red Squirrel Karl Vernes1,* and Nelson Poirier2 Abstract - A Turdus migratorius (American Robin) nest was found in southern New Brunswick, Canada, containing 52 mature sporocarps (“truffles”) of Elaphomyces granulatus (false truffle), a species of hypogeous fungus common across North America. Teeth marks on the truffles indicated they had been cached in the nest by a Tamiasciurus hudsonicus (red squirrel). The truffles appeared to have been air-dried before caching and were well preserved. Mean (± SD) weight of each truffle was 3.3 ± 1.4 g, with a total weight of cached material of 173 g. Although caching of epigeous fungus by squirrels is well documented in the literature, records of cached hypogeous fungi are relatively uncommon, and caches involving disused bird nests appear to be rarely encountered. Introduction Although Tamiasciurus hudsonicus (Erxleben) (red squirrels) are known to rely heavily on conifer seeds for nutrition (Hurley and Robertson 1990, Rusch and Reeder 1978, Steele 1998), they also consume a wide variety of foods such as nuts, buds, fruits, bark, small mammals, fledgling birds (Klugh 1927, Layne 1954, Smith 1968), mushrooms (Buller 1920, Cram 1924, Currah et al. 2000, Dice 1921, Smith 1968), and a great variety of hypogeous (“truffle-like”) fungi (Fogel and Trappe 1978, Smith 1968, Vernes et al. 2004). In southern New Brunswick, Canada, the diet of the red squirrel can comprise anywhere between 45 and 95% fungus, with fungal dependency related to season, and possibly, the variability in conifer seed production and availability (Vernes et al. 2004). Red squirrels in southern New Brunswick consume at least 19 species of truffle-like hypogeous fungi, but the diversity changes seasonally, being high in summer (11–16 taxa), low in fall (5 taxa), and remaining low during winter and spring (3–7 taxa; Vernes et al. 2004). Fungi consumed in the winter are mostly from sporocarps collected, dried, and cached in the summer and fall (Hardy 1949, Murie 1927, Smith 1968). Red squirrels are usually “larder hoarders” (Steele 1998), caching large quantities of food items in a few selected locations. The most commonly seen (and documented) squirrel larder is the cache of conifer cones stored on the forest floor, usually beneath a midden of discarded cone fragments (Hatt 1943, Steele and Koprowski 2001). Caches containing fungi are less commonly documented, probably because these are usually hidden within tree 1Ecosystem Management, The University of New England, Armidale, New South Wales 2351, Australia. 2PO Box 25091, Moncton, New Brunswick E1C 9M9, Canada. *Corresponding author - 146 Northeastern Naturalist Vol. 14, No. 1 hollows, in “witches brooms” (a dense cluster of twigs in a tree caused by an environmental or biological stressor) high in the canopy, and within dead standing trees (Buller 1920, Cram 1924, Hardy 1949, Laursen et al. 2003). Methods and Results In April 2002, a cache of Elaphomyces granulatus Fries (false truffles) was brought to our attention in a suburban backyard in the city of Moncton, NB (46°07'N, 64°41'W). The cache was found on the margin of a forested block, abutting a relatively new housing subdivision. The cache was unusual in that the truffles had been stored within a nest (Fig. 1) made by a Turdus migratorius Linnaeus (American Robin). A robin had been observed using the nest during the preceding summer (2001), and a red squirrel had been seen active in the vicinity of the nest later that year, so the squirrel may have begun using the nest following fledging of chicks and migration south by the robins prior to winter. The nest was approximately 2 m above the ground in a young Abies balsamea L. (balsam fir) tree. In total, 52 E. granulatus truffles had been stored in the nest (Fig. 2), and most of the truffles bore the teeth marks of a small mammal (Fig. 3), presumably made when the truffles were gathered and transported to the cache. Using museum skulls (teaching collection of Mount Allison University, NB) from red squirrels (N = 10), Tamias striatus Linnaeus (eastern chipmunks; N = 2) and Glaucomys sabrinus Shaw (northern flying squirrels; N = 3) collected in southern New Figure 1. Robins’ nest in a young balsam fir tree in suburban Moncton, NB, packed by a red squirrel with 52 false truffles. 2007 K. Vernes and N. Poirier 147 Brunswick, we were able to confidently match the bite marks to a red squirrel. Our examination of these skulls suggested that eastern chipmunk skulls and teeth were too small to have made the puncture marks, while the lower incisors of northern flying squirrels were too broad for a suitable match. However, the upper and lower incisors of the red squirrel skulls articulated well with the bite marks. Figure 2. Robins’ nest and the false truffles that had been stored within it by a red squirrel. Figure 3. Example of the bite marks (indicated by arrows) seen on false truffles that we attributed to a Tamiasciurus hudsonicus (red squirrel), based upon the shape and size of incisors examined from the three species of small sciurids that potentially occurred at the study site. 148 Northeastern Naturalist Vol. 14, No. 1 Mean (± SD) weight of each truffle recovered from the nest was 3.3 ± 1.4 g (range 1.2–6.8 g), with a total weight of the cached fungus being 173 g. The truffles were preserved in reasonably good condition, although those lower in the nest had a light covering of mould on their surface. The general lack of deterioration of the truffles, despite them being packed tightly together, suggests that they might have been air dried by the squirrel elsewhere before caching, but we have no direct evidence for this. That the cache was found towards the end of winter is probably also an indication that the squirrel that preserved and stored the fungus either died during the winter before the cache could be utilised or misplaced the location of the cache. Discussion Caching of epigeous (above-ground “mushroom”) fungi by red squirrels is well documented in the literature. Buller (1920), Cram (1924) and Murie (1927) observed that red squirrels dried mushroom fungi in summer and fall, doing so by hanging them among the branches of trees before storing them in knot holes, hollow branches, and nests of twigs high in the canopy, as well as in holes beneath logs and stumps at ground level. In Alaska, Laursen et al. (2003) reported that red squirrels cache both epigeous and hypogeous fungal sporocarps in “witches brooms” caused by mistletoe infection of spruce trees. Garnett et al. (2004) also report Sciurus aberti Woodhouse (Abert’s squirrel) using “broomed” Pinus ponderosa Douglas ex C. Lawson (ponderosa pine) regularly as cache sites in northern Arizona. Similarly, Sciurus vulgaris Linnaeus (European red squirrel), a scatterhoarder, has been observed drying and caching fungi on the branches of trees in Scotland (Lurz and South 1998). In a singular observation, Dice (1921) noted that a red squirrel had packed dried mushrooms into empty cans in an abandoned cabin in Alaska after first drying them on shelves and other surfaces, showing the adaptability and opportunism displayed by the species in utilising novel cache sites. Relatively fewer records of caches of hypogeous (“truffle-like”) fungi have been reported, although Hardy (1949) gives a detailed account of a red squirrel cache in a burnt-out tree stump in British Columbia containing 59 sporocarps belonging to 13 species of fungi, many of which were hypogeous taxa. The earliest and most detailed treatment of fungal caching by red squirrels was by Buller (1920), who presented several accounts of fungal caches by red squirrels, and was the first to report that squirrels dry fungi in the branches of trees. Buller (1920) also recounts a letter received by him from a resident of Manitoba, Canada, that states “The chief place I have found fungus stores have been woodpeckers’ holes, hollow trees, and birds nests— especially crows’ nests.” However, further detail concerning the use of birds’ nests as cache sites for fungus are lacking from that account, and we could find no other accounts in the literature of birds’ nests as cache sites, suggesting that this phenomenon is rarely observed. 2007 K. Vernes and N. Poirier 149 Acknowledgments We thank Noella Gagnon for bringing this observation to our attention, and Felix Bärlocher, Mount Allison University, for hosting the senior author while on study leave, during which time this paper was prepared. Colleen Barber, David Richardson, and two anonymous referees made suggestions that improved an earlier draft of the manuscript. Literature Cited Buller, A.H.R. 1920. The red squirrel of North America as a mycophagist. Transactions of the British Mycological Society 6:355–362. Cram, W.E. 1924. The red squirrel. Journal of Mammalogy 5:37–41. Currah, R.S., E.A. Smreciu, T. Lehesvirta, M. Nieme, and K.W. Larsen. 2000. Fungi in the winter diets of northern flying squirrels and red squirrels in the boreal mixedwood forests of northeastern Alberta. Canadian Journal of Botany 78:1514–1520. Dice, L.R. 1921. Notes on the mammals of interior Alaska. Journal of Mammalogy 2:20–28. Fogel, R., and J.M. Trappe. 1978. Fungus consumption (mycophagy) by small mammals. Northwest Science 52:1–31. Garnett G.N., R.L. Mathiasen, and C.L. Chambers. 2004. A comparison of wildlife use in broomed and unbroomed ponderosa pine trees in northern Arizona. Western Journal of Applied Forestry 19:42–46. Hardy, G.A. 1949. Squirrel cache of fungi. The Canadian Field-Naturalist 63:86–87. Hatt, R.T. 1943. The pine squirrel in Colorado. Journal of Mammalogy 24:311–345. Hurley, T.A., and R.J. Robertson. 1990. Variation in the food hoarding behaviour of red squirrels. Behavioural Ecology and Sociobiology 26:91–97. Klugh, A.B. 1927. Ecology of the red squirrel. Journal of Mammalogy 8:1–32. Laursen, G.A., R.D. Seppelt, and M. Hallam. 2003. Cycles in the forest: Mammals, mushrooms, mycophagy, mycoses, and mycorrhizae. Alaska Park Science, Winter: 13–19. Layne, J.N. 1954. The biology of the red squirrel Tamiasciurus hudsonicus loquax in central New York. Ecological Monographs 24:227–267. Lurz, P.W.W., and A.B. South. 1998. Cached fungi in non-native conifer forests and their importance for red squirrels (Sciurus vulgaris L.). Journal of Zoology London 246:468–471. Murie, O.J. 1927. The Alaska red squirrel providing for winter. Journal of Mammalogy 8:37–40. Rusch, D.A., and W.G. Reeder. 1978. Population ecology of Alberta red squirrels. Ecology 59:400–420. Smith, C. 1968. The adaptive nature of social organisation in the genus of tree squirrels Tamiasciurus. Ecological Monographs 40:349–371. Steele, M.A. 1998. Tamiasciurus hudsonicus. Mammalian Species 586:1–9. Steele, M.A., and J.L. Koprowski. 2001. North American Tree Squirrels. Smithsonian Institution Press, Washington, DC. 201 pp. Vernes, K., S. Blois, and F. Bärlocher. 2004. Seasonal and yearly changes in consumption of hypogeous fungi by northern flying squirrels and red squirrels in old-growth forest, New Brunswick. Canadian Journal of Zoology 82:110–117.