N19 2015 Northeastern Naturalist Notes Vol. 22, No. 4 B. Heinrich American Chestnut Caching by Red Squirrels Bernd Heinrich* Abstract - I observed Tamiasciurus hudsonicus (Red Squirrel) harvesting Castanea dentata (American Chestnut) fruits in 2 different manners: they either snipped off relatively immature fruit (burrs) and chewed them open on the ground to feed on the unripe seeds, or they foraged on the tree as the ripened fruit opened and released their seeds, carried 1 seed at a time down to the ground, and cached them. I also saw Cyanocitta cristata (Blue Jay) on the trees, but only after the fruit dehisced. Both Blue Jays and Red Squirrels likely played a significant role in the dispersal of American Chestnut seeds, but the Blue Jays spread primarily single or several seeds per cache, while the Red Squirrels created caches of seeds clustered closely together. Tamiasciurus hudsonicus (Erxleben) (Red Squirrel) make extensive use of conifers. They cut cones from trees, let them fall to the ground, and gather them up into piles or “middens” (Forsyth 1985). As such, they are larder-hoarders (Gerhardt 2004) and they defend a small home-range (Gurnell 1984). Red Squirrels exhibit variable behaviors or personalities (Boon et al. 2008), which may include scatter-hoarding (Hurley and Robertson 1987, 1990), and maple-sugaring that involves running “trap-lines” to harvest maple syrup (Heinrich 1992). At a site in western Maine where I made these observations, Red Squirrels are common and Castanea dentata (Marshall) Borkh. (American Chestnut, hereafter, Chestnut) are non-native, but I introduced 4 seedlings there in 1982. Over 200 surviving pure Chestnut offspring of the 4 seedlings planted at the edge of a clearing in mixed deciduous–hardwood forest have been dispersed in all directions over 9 ha (Heinrich 2014). Only 4 of these plants were growing under the parent trees, and due to the long-distance dispersal of the rest of young trees from the parent tree, the Chestnut seeds were necessarily animal-transported. The numerically most abundant of the seedlings (110 out of 238) were 1–5-y old and growing singly (Heinrich 2014). Until 2012, I had only observed Cyanocitta cristata L. (Blue Jay) routinely carrying off 1 to several Chestnut seeds, and because I had found seedlings growing up to 300 m from the parent trees, it seemed likely that Blue Jays were the primary dispersal agents. Birds are known as scatter-hoarders (Brodin 2010), and each of their caching trips ends at a new location. Thus, how could the sometimes-observed caches of at least 10, 18 and 20 seedlings with attached nuts (Heinrich 2014) have resulted when the Blue Jays could carry at most 5 American Chestnut seeds at a time? Here I describe new observations that solved this riddle, and provide details that pertain to Red Squirrels. In October 2012, when the seeds that produced the clumped seedlings originated, there was neither Quercus sp. (oak) nor Fagus sp. (beech) mast, but the mature Chestnuts that I had planted bore fruit. Blue Jays were few or absent at first, but I observed Red Squirrels in the Chestnut trees from 4 to 7 October. I saw 1 of them on 2 separate tree crowns (the 2 trees were close together). They were snipping off one Chestnut fruit (burr) after another, and I timed a Red Squirrel that snipped off 25 burrs in 5 minutes, and tabulated a total of 737 burrs snipped off that fell to the ground; none of these fruits had yet dehisced their seeds. But by 13 October, when the burrs started to open to reveal the browned nuts, Blue Jays became abundant, and for several days streams of them were flying in all directions carrying off nuts. The woods were dense and the Blue Jays flew far; thus, I could not determine *PO Box 153, Weld, ME 04285; bheinrich153@gmail.com. Manuscript Editor: Michael J. Cramer Notes of the Northeastern Naturalist, Issue 22/4, 2015 2015 Northeastern Naturalist Notes Vol. 22, No. 4 N20 B. Heinrich current-year cache sites. However, I inferred locations of past-year caches by the locations of unrecovered nuts that had sprouted to produce over 200 small trees in previous years (Heinrich 2014). The following fall (2013) no Blue Jays were present at the Chestnut trees at any time, presumably because there was a competing huge crop of beechnuts that they had started visiting earlier and continued to harvest even while the Chestnuts ripened. I found no reason to conduct formal observations at the Chestnut trees, but rather, searched systematically for Chestnut seedlings in the woods. I located primary caches of 1, 2, 3, and sometimes 4 or 5 clumped seedlings at distances up to 300 m from the parent trees that were likely the result of caches made by Blue Jays. I also found the afore-mentioned caches of 10 to 20 one-year-old sprouted Chestnut seeds. These caches were about 5 m apart and 45 m from the parent trees. During October 2014, there was another lack of both beechnut and Quercus rubra L. (Red Oak) acorn mast, but, as they had done every year for at least the previous 5 y, the 4 Chestnut trees produced a large nut-crop. That year, Blue Jays were present even before the burrs opened. One Red Squirrel was uncontested (and stayed silent) in a tree crown (of 2 trees together) where it snipped off burrs for only 1 day. No burrs were snipped off at the other Chestnut tree crown (also of 2 trees) where a second Red Squirrel frequently vocalized as it chased other squirrels. I later observed Blue Jays in the tree crown near this second Red Squirrel after the seeds ripened and the fruits started to dehisce and expose the seeds. While watching the Blue Jays (up to 7 present at one time) to determine their movements and numbers of Chestnuts taken, I saw the 1 Red Squirrel in residence at the tree. It repeatedly ascended the tree and then descended carrying a nut. Each time it reached the ground it ran several meters, stopped to hide the nut under loose leaves, then returned and re-climbed the tree. Within 1 or several minutes, the Red Squirrel came back down with another nut, and carried it to the same spot as before. On some trips, however, it deposited the nut at another spot, also nearby and under the crown of the tree. While the squirrel was up in the tree getting a nut, I rushed to find and examine the 2 spots where it had left nuts. After scraping aside the leaves at those spots, I found 2 caches of 9 and 10 nuts, respectively. The nuts were closely packed together in 1 packet (Figs. 1, 2), and were located 2.4 m and 5.8 m, respectively, from the Chestnut tree trunk. After my count, when the Red Squirrel ran back down the tree trunk with another nut and ran directly to its cache of 10 nuts, it rummaged briefly and then ran on without leaving the nut there. I left and came back an hour later, finding both caches emptied. At the same time that the Red Squirrel had been making the 2 near caches that I found, it also repeatedly ran carrying nuts in the same direction but into the forest, and it returned from the same direction about 2 minutes later to get another nut from the top of the tree. The Red Squirrel’s caching site was out of my view. Estimating the distance by the squirrels’ approximate running speed, I stationed myself in the woods hoping to intersect its path or be near enough to see it cache a seed at the presumed distant cache site or sites. Using this method, I found 1 cache 20 m from the parent tree when the Red Squirrel dropped the nut it was carrying into a hollow stump, which I immediately examined as the animal left and found it to contain 4 nuts. It did not continue caching there and removed the 4 nuts for apparent re-caching somewhere else (see Zhang et al. 2014). Beechnut mast was available near the same site during September 2015, but acorns were again nearly absent that fall in the nearby forest. The Chestnut trees fruited as abundantly as in previous years, and I monitored them from near the beginning of nut ripening on 19 October until 26 October. During this time, I made at least 15 spot check from dawn to dusk throughout each day. Although Blue Jays and Red Squirrels had fed routinely on the N21 2015 Northeastern Naturalist Notes Vol. 22, No. 4 B. Heinrich beechnuts this year, I observed no red Squirrels and no more than 2 Blue Jays at or near the Chestnuts. One Blue Jay occasionally (6 times) qppeared in the 2 Chestnut trees. A single Sciurus carolinensis Gmelin (Eastern Gray Squirrel) fed on the nuts on 3 occasions. No Figure 1. Entrance (in center) to a Red Squirrel cache of 10 Chestnuts. Figure 2. The same cache as shown in Figure 1 after covering leaves were removed. 2015 Northeastern Naturalist Notes Vol. 22, No. 4 N22 B. Heinrich burrs were snipped from the trees, and the Gray Squirrel handled the chestnut burrs and the nuts while remaining on the tree. I observed no competition for the nuts and no caching by any of the 3 potentially nut-caching species. The present observations show that Red Squirrels make nut caches, aside from their well-known cone middens, and they may relocate these caches as well as add nuts to them. Their use of the same site for multiple caching trips contrasts with the scatter-hoarding behavior of food-caching birds (Balda and Kamil 1989, Brodin 2010). Although the repetition of visits to the same cache site may facilitate long-term memory of the location, “putting all the eggs in one basket” risks losses to raiding cache thieves, such as other squirrels. This risk may be counterbalanced by the squirrels’ local residency combined with strong territorial defense (Hurley and Roberson 1990). The differences in Red Squirrel behavior I observed between 2013 and 2014 were likely related to inter- and/or intra-specific competition. The Red Squirrel almost immediately relocated the 3 caches I found while it was in the process of making them, which suggests that it may have detected my presence and perceived the caches to be vulnerable to pilfering; it responded with a counter-strategy (Zhang 20114). However, the Blue Jays, which in aggregate take most of the nuts, are competitors at the tree for the 3–4 days when the nuts are available from the opening burrs. Harvesting the fruit by snipping them off the trees before the Blue Jays could get nuts from them, as occurred most prominently in 2012, may function as a counter-strategy. In 2014, no Red Squirrel, however, was prominent in a tree crown (a duo of 2 trees) until the nuts were opening, when it then competed directly with the Blue Jays present there. This Red Squirrel could potentially have similarly simply dropped nuts for a while to pick them up later, as the 2 Red Squirrels had done with the early-harvested burrs. It would then not have needed to travel back and forth between the crown of the 13-m-tall tree and the ground. However, although nuts inside the burrs 2–3 days before they fully ripen are inaccessible to the Blue Jays and could not be taken by them, the same is not true for the nuts in open burrs; Blue Jays flew to the ground whenever a nut dropped as they were extracting nuts from the multi-seed burrs, and the ground was bare of nuts because they picked them up. By carrying 1 nut at a time, the squirrel precluded competitors from gathering the nuts that had cost time and effort to find in the tree and extract from the burrs. Chestnut fruits open in a relatively synchronous, narrow period (4 days in 2014) and unlike the Blue Jays, Red Squirrels cannot easily travel fast and far. This lack of mobility may also favor the practice of making quick, temporary, local caches, to take advantage of the rich but highly ephemeral food bonanza, and to later relocate the nuts further away to a less-contested site such as into the territory where it has its nest and its midden. The multiple-seed caches (10 or more nuts as determined by number of seedlings) were ~50 m from the source, whereas the farthest of the 3 fresh caches of multiple seeds that I observed was 20 m from the parent tree. Based on these new observations, it is likely that the enigma of the clustered Chestnut seedlings is explained by the fact that Red Squirrels rather than Blue Jays created at least the large, nearby multiple-seed caches. Thus, it appears that both Red Squirrels and Blue Jays are important dispersal agents of American Chestnuts. Acknowledgments. I would like to thank the manuscript editor and 2 anonymous reviewers for their comments on earlier drafts of the manuscript. Literature Cited Balda, R.P., and A.C. Kamil. 1989. A comparative study of cache recovery by three corvid species. Animal Behaviour 38:486–495. N23 2015 Northeastern Naturalist Notes Vol. 22, No. 4 B. Heinrich Boon, A.K., D. Reale, and S. Boutin. 2008. Personality, habitat use, and consequences for survival in North American Red Squirrels, Tamiasciurus hudsonicus. Oikos 117:1321–1328. Brodin, A. 2010. The history of scatter-hoarding studies. Philosophical Transactions of the Royal Society B 365:869–881. Forsyth, A. 1985. 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