The Natural History of Tassel-Eared Squirrels

11. Ecology [Includes Image Plates]

129 Ecology Tassel-eared squirrels were fairly common in the yellow pine association, and were most active early in the morning. . . . The squirrels were feeding on the bark of the yellow pine twigs and the ground under several young trees was covered with branch-tips. . . . One was seen chased by the much smaller chickaree. —J. E. Hill, “Notes on Mammals of Northeastern New Mexico,” 1942 This chapter is dedicated to Dr. Jim Keith for all of his research with Abert’s squirrels. Introduction T he importance of the relationship between the tassel-eared squirrel and the ponderosa pine forest was first noted in 1925 when Taylor stated, “Its attractive presence could ill be spared from the woods” (ref. 1). Bailey wrote of a conversation he had regarding tasseleared squirrels on the South Rim of the Grand Canyon: “[T]he gardener at El Tovar Hoteltoldme he sawone ofthe bigsquirrelsbringtheconeofa yellow pine into the hotel flower garden and bury it among his snapdragons . This seems to fix the storing habit among these squirrels sufficiently to place them on the list of useful tree planters” (ref. 2). Later Bailey wrote again about the importance of squirrels and their cone-burying habits: “If it were not for the squirrels, the pine cones would lie on the ground or scatter their seeds to be eaten by mice and jays. Consequently, although many branches are trimmed and many seeds are eaten by these small tenants of the forest, it is still evident that they are great planters and thus conservators, of the forest trees on which they depend for their living” 11 130 C H A P T E R E L E V E N (ref. 3). Abert’s squirrels bury pine cones with their “legs rapidly crossing and re-crossing with their familiar covering up and patting down motions” (ref. 4). Tassel-eared squirrels are considered to be beneficial to the forest because they act as “seed spreaders” (ref. 5). When green ovulate cones are buried by squirrels and not later located and eaten, many seeds may germinate (ref. 6). All the feeding activities of tassel-eared squirrels, obligate herbivores in ponderosa pine forests, from digging for false truffles to consuming seeds from ovulate cones, directly affect the forests (ref. 7). Digging opens the litter layer to the parent soils while seed eating can in some cases eliminate an entire tree’s reproductive effort for a year. Feeding on inner bark with the concomitant loss of green needles influences nutrient cycling. Numerous ecological studies have examined the complex relationship between the tassel-eared squirrels and the ponderosa pine forests. Ecology of Tassel-Eared Squirrels and Ponderosa Pines Tassel-Eared Squirrels and Ponderosa Pine Tree Morbidity and Mortality Tree mortality due to defoliation of ponderosa pine trees by tassel-eared squirrels as they feed on inner bark has been evaluated in a number of studies with differing conclusions. Taylor reported excessive defoliation by squirrels during their feeding activities to be rare. He examined 942 trees and noted that only three trees appeared to be severely damaged and that “branch-cutting” activities could be beneficial or neutral to the tree rather than being considered harmful (ref. 8).Two years later Taylor wrote, “One tree was observed from which most of the foliage had been trimmed by squirrels. As with the Abert most of the work of the white-tail [Kaibab] was apparently diffuse . . . if the animals did become superabundant they might do serious damage to the western yellow pine, through their branch-cutting and cone-scaling activities” (ref. 9). In another report the next year, Taylor wrote that squirrels “ordinarily do little damage but in a few areas squirrels have defoliated and caused the death of some trees” (ref. 10). Hall attributed the death of one ponderosa pine tree to squirrel clipping activities but he cautioned that this was an isolated case in all of his work with the Kaibab squirrel over ten years. He noted that trees that had been fed on by Kaibab squirrels for inner bark did show a difference PLATE 3 San Francisco Peaks in northern Arizona where Dr. Woodhouse first discovered and named the Abert’s squirrel. Photograph by Sylvester Allred. PLATE 1 Col. Abert’s squirrel by John Woodhouse Audubon. Plate 153 from the first octavo edition of The Quadrupeds of North America. Hand-colored stone lithograph by J. T. Bowen, 1854. Used by permission of Minniesland.com...