Common Components of Orchard Ground Cover Selected as Food by Captive Woodchucks

Abstract

I examined diet selection by captive woodchucks (Marmota monax) for 20 species of plants commonly found in ground cover in Connecticut orchards. Cafeteria-style feeding trials indicated that the most frequently selected foods were dandelion (Taraxacum officinale) and common plantain (Plantago major), whereas orchard grass (Dactylis glomerata), Virginia creeper (Parthenocissus quinquefolia), and common toadflax (Linaria vulgaris) were selected least often. Sequential elimination of the most frequently selected foods resulted in increased use of mugwort (Artemisia vulgaris), campion (Lychnis alba), red clover (Trifolium pratense), aster (Aster vimineus), poison ivy (Rhus radicans), common strawberry (Fragaria virginiana), old-field cinquefoil (Potentilla simplex), bird vetch (Vicia cracca), and goldenrod (Solidago rugosa). Management of ground cover to reduce the abundance of plant species selected by woodchucks might reduce woodchuck numbers and the problems they cause. J. WILDL. MANAGE. 54(3):412-417 Woodchucks inhabit orchards throughout eastern North America, and damage due to their burrowing (Byers 1984) and gnawing of fruit trees (Swihart and Conover 1988, Swihart 1990) is a problem for growers. Phillips et al. (1987) estimated annual losses of $240,000 because of woodchuck activity in orchards in the Hudson Valley, New York. Population reduction typically is used to lessen problems caused by woodchucks, although immigration and increased fecundity of survivors may limit the utility of this type of control (Davis et al. 1964). Ground cover in orchards typically is composed of numerous herbaceous species that woodchucks eat. Reducing the abundance of commonly selected plants while encouraging the growth of less palatable species may lessen the suitability of orchards for woodchucks. Information on food habits of woodchucks consists primarily of qualitative observations (Hamilton 1934, Twichell 1939, Grizzell 1955). Moreover, these studies did not examine the relative abundance of each species in determining diet selection. My objectives were to examine selection by captive woodchucks for 20 plant species found in orchards and to determine the extent to which diet selection was affected by removal of the most readily eaten species. I thank M. R. Conover, G. L. Kirkland, Jr., P. M. Picone, and an anonymous reviewer for constructive comments on the manuscript, and P. M. Picone and A. DeNicola for diligent assistance with feeding trials. METHODS Feeding trials were conducted using 15 adult woodchucks (8 M, 7 F) captured in early spring of 1988 and 1989 in agricultural regions of western and central Connecticut. Woodchucks were housed individually in 1.5x 1.5x 0.9-m outdoor pens constructed of galvanized wire mesh and containing a plywood nest box. Animals were kept in cages with access to unlimited rodent chow and water for 10-30 days prior to initiation of feeding trials to permit acclimation to their surroundings and to a diet of rodent chow. Feeding trials were conducted in June and July 1988 and in June 1989. Vegetation used in trials was collected in or near orchards in central Connecticut. Vegetation not used immediately after collection was stored in a cool room (10 C), and any vegetation kept in storage >48 hours was discarded. Vegetation was collected from the same sites in both years to reduce variability in vegetation due to site characteristics. Nonetheless, differences in environmental conditions between years could have caused differences in plant quality and, consequently, selection of plants by woodchucks. However, selection by woodchucks was highly consistent between years (selection between 1988 and 1989, Pearson r = 0.78, 18 df, P 0.10 for all plant species). Hence, results were pooled across years and sexes prior to anal-