SUMMER DIET COMPOSITION OF IN ROCKY MOUNTAIN NATIONAL PARK,

Jason D. Dungan' and R. Gerald Wright'

'Department of Fish and Wildlife Resources, University of , P.O. Box 441136, Moscow, ID 83844-1136, USA; 2USGS Idaho Cooperative Fish and Wildlife Research Unit, Department of Fish and Wildlife Resources, University of Idaho, P.O. Box 441136, Moscow, ID 83844-1136, USA

ABSTRACT: Summer diet composition of habituated adult moose (Alces alces) in Rocky Mountain National Park, Colorado, was determined using direct observations and fecal analysis. Direct ob- servations determined moose ate 20 different species, including 6 (Salix spp.) species, which comprised 91.3% of the overall diet from June through mid-September. Geyer willow (Salix geyeriana) accounted for 45.1% of summer diets. Other species included mountain alder (Alnus in- cana, 2.5%), quaking aspen (Populus tremuloides, 1.1%), and bog birch (Betula glandulosa, 1.0%). Aquatic accounted for 1.9%, forbs 1.1%, and grasses 0.9%. Moose ate 11 different species of woody browse, which comprised 96.9% of the diet. Species diversity in the diet peaked in July with 18 different species, including 7 species of non-woody browse. Fecal analysis showed moose consumed 79.3% willow; 11.9% less than direct observations indicated. Fecal analysis identified Carex spp. as a major contributor to moose summer diets (8.7%); a genus not identified by direct observation. Fecal analysis could not identify forbs, willow, or other to the species level, but identified all major genera (> 1%) contributing to moose summer diets that were indicated by direct observations, except quaking aspen (1.1%).

ALCES VOL. 41: 139-146 (2005)

Key words: Alces alces, diet, food habits, moose, willow, woody browse

Historically, moose (Alces alces shirasi) major changes in plant community composi- were rare in Colorado and early sightingstion and structure (Augustine and McNaugh- recorded in Colorado were believed to beton 1998). Herbivory is a major concern of moose that wandered into the state from RMNP where large numbers of Rocky Moun- northwestern (Bailey 1944). Thetain (Cervus elaphus) occur. Managers Colorado Division of Wildlife (CDOW) are particularly concerned about effects on introduced two groups of 12 moose near the riparian willow (Salix spp.) and upland town of Rand, Colorado, in 1978 and 1979; communities, based on visual appearance of 13 km west of Rocky Mountain National Park short-hedged willow on elk winter range. (RMNP). The objective was to establish a In a recent study, elk herbivory was found viable resident moose population in the area.to suppress heights, leader lengths, and an- In June of 1980, the first moose was observed nual production of willow, and herbaceous within the park, and the first moose to win- productivity of willow sites within the park ter in the park was recorded in 1985-1986 (Zeigenfuss et al. 1999). (Stevens 1988).Presently between 61-66 High densities of moose have also been moose are estimated to summer in the park shown to influence the dynamics and structure (J. Dungan, University of Idaho, Moscow, of ecosystems. Bark stripping by moose in Idaho, unpublished data). Denali National Park, , may increase Large mammalian herbivores can cause the rate of succession in aspen-spruce com-

139 Alces MOOSE SUMMER DIET COMPOSITION - DUNGAN AND WRIGHT ALCES VOL. 41, 2005

munities by killing trees (Miquelle and Van term effects of moose browsing on riparian Ballenberghe 1989).Similar results were communities from Alaska to RMNP, is not found in Isle Royale National Park, Michigan, yet understood. The purpose of this study where high rates ofmoose browsing depressed was to document summer diet composition nitrogen mineralization and net primary pro- of moose in RMNP. duction ofboreal forest ecosystems (Pastor et al. 1993). Furthermore, McInnes et al. (1992) STUDY AREA showed that moose herbivory reduced tree This study was conducted in RMNP dur- biomass and production, and increased shrub ing the summers of 2003 and 2004. RMNP and herb biomass at Isle Royale. is located in north-central Colorado just west Winter food supply is generally con- of Estes Park. RMNP covers an area of 1,075 sidered the limiting factor in some moose km2 and ranges from 2,389 m to 4,345 m in populations (Crete 1989, Kufeld and Steinert elevation. The park lies astride the continental 1990, MacCraken et al. 1997, Zheleznov-Chu- divide and the west and east side differ in kotsky and Votiashova 1998). Woody browse climate. Annual precipitation ranges from is usually the only food supply available for37.6 to 51.7 cm. Temperatures range from moose during the winter, and therefore moose highs in July and August of 24°C to lows in diet and habitat studies have focused on use, December-February of -17°C (Monello and availability, and quality of winter browse Johnson 2003). (LeResche and Davis 1973). Few studies have We conducted this study predominantly examined use of summer habitat, althoughon the west side of the park within the summer diets are generally 1.5 -3 times more Colorado River Drainage and within higher nutritious than winter diets (Schwartz 1992), elevation meadows east of the Continental and summer is a key period in which moose Divide. The study was conducted at 2 dis- build up fat reserves that take them through tinct elevational strata, below 3,000 m (low the winter. Knowledge of moose summerelevation sites) and above 3,000 m (high diets benefits resource managers in making elevation sites), because of differences in decisions on managing moose habitat. plant species composition, distribution, and Peek (1974) reviewed 41 food habit stud- plant morphology.Lower elevation sites ies in North America, of which 18 were fromtend to be comprised of a greater variety of the intermountain west, but none as far southplant species. Plants tend to be more sparsely as Colorado. Five of the 18 studies includeddistributed, and to be taller with longer leader summer food habits, and revealed even greater lengths and greater biomass, than plants at variation between areas than those on the high elevation sites. winter range (Peek 1974). Summer diet stud- Low elevation riparian meadows are ies have increased (Joyal and Sherrer 1978, characterized by large stands of geyer wil- Butler 1986, Van Ballenberghe et al. 1989), low (Salix geyeriana), mountain willow but none have investigated the southern extent (Salix monticola), drummond willow (Salix of the . drummondiana), plane-leaf willow (Salix In North Park, willow was the mostplanifolia), and smaller stands of whiplash commonly selected habitat by moose in allwillow (Salix lasiandra), and wolf willow seasons between 1991 and 1995 (Kufeld and (Salix wolfii).Other common species are Bowden 1996). Similarly, willow comprised beaked sedge (Carex utriculata), bog birch about 80-85% of the diet of wild adult moose (Betula glandulosa), mountain alder (Alnus in Denali National Park during the summerincana), marsh reed grass (Calamagrostis (Van Ballenberghe et al. 1989). The long- canadensis), white clover (Trifoliumrepens),

140 Alces ALCES VOL. 41, 2005 DUNGAN AND WRIGHT - MOOSE SUMMER DIET COMPOSITION and strawberry (Fragaria ovalis). These areas These samples were bagged, oven-dried at are surrounded by stands of ponderosa pine 60°C for 48 hours, and weighed in accor- (Pinus ponderosa), Douglas fir (Pseudotsuga dance with methods described by Renecker menziesii), quaking aspen (Populus tremuloi- and Hudson (1985). Average dry weight per des), and narrowleaf cottonwood (Populusbite (g/bite) for each size and species was angustifolia). High elevation meadows are calculated. Diet composition was based on characterized by large stands ofplane-leafwil- percentage dry weight of species consumed low, wolf willow, and bog birch. Surrounding by moose. This was derived by multiplying trees include quaking aspen, lodgepole pine the number of bites taken of each species in (Pinus contorta), and subalpine fir (Abies each size class by the average dry weight per lasiocarpa) (Beidleman et al. 2000). bite (Van Ballenberghe et al. 1989). Fresh fecal samples were collected from METHODS observed moose during foraging bouts. Over 3 million people visit RMNP an- Sample size ranged from 6 to 17 per month, nually. Viewing wildlife is a major visitorand included pellets collected in October activity and traffic jams result when large and November, while walking low elevation animals such as moose are visible from parktransects, to look at early winter diets. These roads. As a result, moose within RMNP are samples were frozen and sent to the Wildlife accustomed to people and their habituation Habitat Lab at State University enabled us to directly observe feeding be- for microhistological analysis. Sub-samples havior and estimate diet composition. From of each fecal pellet group were combined 1 June through 15 September we observedwith others from the same month and year. the feeding behavior of moose at distancesFecal samples were blended with water, between 5-20 m. We recorded feeding data washed on a fine wire screen (200 mesh), and using hand-held voice recorders. Feeding data stained with a lactophenol blue stain. Rela- were grouped into feeding periods (bouts)tive cover (Korfhage 1974, Davitt 1979) of defined as any span greater than 15 minutes in plant cuticle and epidermal fragments were which the moose fed continuously. Miquelle quantified for 25 randomly located micro- and Jordan (1979) reported more than 95% scope views on each of four slides (total 100 of all bites recorded occurred during suchviews) per month. A 10 square x 10 square bouts. We counted individual bites takengrid was used to measure area covered by by foraging moose, and bites were classified each positively identified fragment observed by plant species when possible. Individual at 100x magnification, and measurements of moose were followed as long as possible, area covered were recorded by plant genus and each continuous span was considered a and species. Percent diet composition was single observation set. Bite counts were not calculated by dividing cover of each plant conducted at night for observer's safety andby total cover observed for all species, then compliance with park regulations. multiplying by 100. During feeding periods the sizes of We compared differences in percentages all bites were recorded to estimate intake of major plant species between years, eleva- rates, and bites were classified as small (1-5 tions, months, and sexes for bite count data leaves), medium (5-10 leaves), or large (> 10 using a 1-way ANOVA. Salix species were leaves). After each observation set, simulated pooled, and all percentages were Arcsine moose bites were collected by clipping 10-20 transformed in accordance with Krebs (1999). samples/species in each of the three sizes as Experimental units were observations (n = closely to the observed bite size as possible. 54), and pair-wise differences were located

141 Alces MOOSE SUMMER DIET COMPOSITION - DUNGAN AND WRIGHT ALCES VOL. 41, 2005

Table 1. Summary of moose feeding data collected in Rocky Mountain National Park, Colorado from June 1st through September 15th, 2003 and 2004.

Month Site (Elevation) Observations Female Male Feeding Bouts Bites

June Low 15 4 11 27 9,807

July Low 17 4 13 60 20,324

High 3 0 3 15 11,013

August Low 7 3 4 32 15,277 High 4 0 4 17 10,544 September Low 6 0 6 21 7,692

High 2 0 2 5 2,322

Totals 54 11 43 177 76,979 using the Tukey HSD procedure. Differences diets. Geyer willow accounted for 45.1% of were considered significant at alpha < 0.05, summer diets followed by plane-leaf willow and all statistics were performed using SAS (22.7%), mountain willow (11.7%), and drum- 8.3 (SAS Institute Inc., Cary, North Carolina) statistical software. Table 2. Percentage of plant species consumed by moose from June 1st through September 15th 2003 and 2004 in Rocky Mountain National RESULTS Park, Colorado.Percentages were based on We recorded feeding data on 11 female 76,979 bites classified to species and their as- and 43 male moose for a total of 54 observa- sociated weights, measured in grams/bite. tion sets (Table 1). Over 75,000 bites were counted during 177 feeding bouts (Table Species Diet % 1).Data from direct observations showed Salix geyeriana 45.10 no difference between sexes and elevations S. planifolia 22.70 (P> 0.05), but showed a significant difference S. monticola 11.70 (F=3.51; df= 3,48; P = 0.02) among months for S. drummondiana 9.90 mountain alder. Moose consumed significant- Alnus incana 2.50 ly more mountain alder in late summer (Sep- S. wolfii 1.50 tember) than early summer (June). Likewise, Aquatic spp. 1.30 a significant difference was found between Populus tremuloides 1.10 years for western dock (Rumex aquaticus) Betula glandulosa 0.97 (F = 4.15; df = 1,48; P = 0.04) and trian- Grasses 0.91 gular leaf Senecio (Senecio triangularis) Cirsium spp. 0.71 (F = 5.71; df = 1,48; P = 0.02). Moose ate Rumex aquaticus 0.47 significantly more western dock in 2003 and Senecio triangularis 0.32 significantly more triangular-leaf Senecio in S. lasiandra 0.29 2004. Other than the forementioned species, Nuphar lutea ssp. Polysepala 0.21 moose ate similar diets among months (P > Pentaphylloides floribunda 0.16 0.05) and years (P > 0.05). All bite count Psychrophila leptosepala 0.03 data were therefore pooled, for all animals, Mentha spicata 0.02 sexes, months, and years to estimate summer Pincus contorota Trace' diet composition (Table 2). Moose consumed Shepherdia canadens s Trace' 11 different species of woody browse, which comprised 96.9% of the diet.Six willow 'Trace species representedless than 0.01 % of species comprised 91.3 % of moose summer the diet.

142 Alces ALCES VOL. 41, 2005 DUNGAN AND WRIGHT - MOOSE SUMMER DIET COMPOSITION mond willow (9.9%). Geyer willow ranked (1.1%, Table 4). With the exception of Carex first each month except in August 2003 when spp., both techniques showed similar results it ranked third behind mountain willow and (Table 4). drummond willow.Other woody species included mountain alder (2.5%), quaking DISCUSSION aspen (1.1%), and bog birch (1.0%). Aquatic Moose summer diets in RMNP consisted species accounted for 1.9%, forbs 1.1%, and of 11 different species of woody browse, grasses at 0.9%. Species diversity peaked inwhich accounted for roughly 97 % ofthe over- July with moose eating 18 different species, all diet. These results are similar to those found including 7 species of non-woody browse. by Van Ballenberghe et al. (1989) in Denali Monthly fecal analysis for 2003 showedNational Park, Alaska, where woody species moose relied more heavily on species other made up 96% of moose summer diets, and than willow in June, most notably Carex spp. Joyal and Scherrer (1978) in Mont-Tremblant (46.4%, Table 3), then increased willow con- Park, Quebec, where moose summer diets sumption in July with a peak inAugust at 90%. consisted of 100% woody browse. Moose in In September, willow consumption began to RMNP use riparian willow communities dur- decrease and early winter diets included spe- ing the summer, which contain little aquatic cies other than willow, most notably conifer vegetation or forbs. Moose were observed needles (34.1%), shrubs (18.1%), and Carex eating 9 different non- woody species. Stud- spp. (11.6%, Table 3). ies in less mountainous habitats have found Fecal analysis data were pooled for all moose consume larger proportions of forbs months and years, with the exception Octo- (25%, LeResche and Davis 1973; 70.6%, ber/November 2003, to show summer moose Knowlton 1960) and aquatics (9.3%, McMil- diet composition (Table 4).Fecal analysis lan 1953) than those in RMNP. Forbs and showed moose consume 79.3% willow, aquatics may contain higher concentrations which is 11.9% less than direct observations of important minerals (Belovsky 1978), and indicated (Table 4). Fecal analysis identified have higher digestibility levels than woody Carex spp. as a major contributor to moosebrowse (LeResche and Davis 1973). Forbs summer diets (8.7%), and was not identified and aquatics only accounted for 2.4% of the by direct observation.Fecal analysis was overall summer diet of moose in RMNP. not able to identify forbs, willow, or shrubs Moose ate 6 willow species comprising to the species level, but identified all major 91.3% of their summer diets, with geyer genera (> 1%) identified by direct observa- willow accounting for 45.1%. Results were tions with the exception of quaking aspen similar to those found by McMillan (1953) for

Table 3. Percent of major plant species consumed by moose in Rocky Mountain National Park, Colo- rado per month for 2003, and by year for 2004, as indicated by fecal analysis.

Plants Jun-03 Jul-03 Aug-03 Sep-03 Oct/Nov 03 2004 Grasses 2.10% 0.00% 0.60% 0.80% 8.90% 7.70% Carex spp. 46.40% 5.00% 0.10% 3.80% 11.60% 3.60% Salix spp. 48.00% 88.20% 90.00% 82.90% 25.30% 81.40% Shrubs 0.40% 6.00% 9.30% 11.50% 18.10% 6.90% Conifer needle 0.70% 0.00% 0.00% 0.00% 34.10% 0.20% Forbs 2.40% 0.60% 0.00% 1.00% 2.00% 0.00% Sphagnum Moss 0.00% 0.00% 0.00% 0.00% 0.00% 0.20% Insect 0.00% 0.20% 0.00% 0.00% 0.00% 0.00%

143 Alces MOOSE SUMMER DIET COMPOSITION - DUNGAN AND WRIGHT ALCES VOL. 41, 2005

Table 4. Percent diet composition of major plant showed the same trend, with exception of species consumed by moose in Rocky Mountain June bite count data, suggesting moose eat National Park, Colorado from June 1st throughwillow when available biomass and nutrients September 15th, 2003 and 2004, using directare high (Stumph 2005) and rely less heavily observations and fecal analysis. All months and on willow in spring and fall when available years were pooled for both techniques. biomass and nutrients are lower. Early winter Species Fecal Analysis Bite Count fecal analysis showed willow comprised only Salix spp. 79.3 91.3 25.3 % of the diet, whereas conifer needles Carex spp. 8.7 made up 34.1%, and grasses, forbs, and Shrubs 6.8 3.6' sedges made up 22.5 %. Forbs and grasses Grasses 4.3 0.91 comprised relatively larger percentages of fall Aquatics 0.11 1.982 diets than winter diets (Peek 1974). During Populus tremuloides 1.12 both years we observed moose moving out Forbs 0.51 1.083 of the lower riparian willow communities, Conifer needles 0.19 Trace' with the onset of the rut, and moving into Insects 0.02 higher more heavily forested areas ofthe park, possibly giving a reason for the large percent 'Shrubs consisted of Alnus incana, Betula glan- of conifer needles in early winter diets.In dulosa, Pentaphylloides floribunda, and Shep- a study conducted from December 1991 to herdia Canadens is. November 1995, moose from North Park, 2Aquatics consisted ofAquatic spp., Nuphar lutea Colorado, tended to winter at lower elevations spp. Polysepala, and Rumex aquaticus. and move to higher elevations during spring, 3Forbs consisted of Cirsium spp., Mentha spi- summer, and fall (Kufeld and Bowden 1996). cata, Psychrophila leptosepala, and Senecio Winter transect data showed little use of low triangularis. elevation riparian willow communities from 4Trace species represented less than 0.01 % of October through December for both years. the diet. were the primary forage plants in 5 moose in Yellowstone National Park (willowout of 6 winter diet studies reviewed by Peek 88.5%) and Van Ballenberghe (1989) in Denali (1974), and Risenhoover (1987) reported National Park (81.5%). Similarities of diet that willow comprised 94.3% of winter diets composition of moose in RMNP and moosein Denali National Park.Stevens (1970) in Denali National Park suggest use of veryreported timber types received 82% of total similar habitats during the summer. Willowuse during the winter in the Gallatin region of habitats not only provide a high quality woody . October/November fecal analyses browse for consumption (LeResche and Davis coupled with winter trans e ct data suggest that 1973) but are also used extensively for cover willow may not constitute a large proportion (Kufeld and Bowden 1996). of moose winter diets in RMNP, although a Fecal analysis showed moose rely morecomprehensive study of winter diets has not heavily on grasses, sedges, and forbs (50.9%)been performed. in early summer than woody browse (49.1%). Similar results were achieved using bite Peek (1974) found that grasses and sedges count data and fecal analysis. Direct observa- were seldom consumed other than in spring, tions failed to detect the large amount of sedges when digestibility and nutrient content are consumed by moose in early summer, which high.Consumption of willow species in-was largely affected by adult movements creased in July, peaked in August, and started during June. Older, more habituated moose to decline in September. Both techniqueshad not yet moved to summer range from

144 Alces ALCES VOL. 41, 2005 DUNGAN AND WRIGHT - MOOSE SUMMER DIET COMPOSITION winter range, necessitating that our sample be 62:1165-1183. focused on younger, less habituated moose. BAILEY, A. 1944. Records of moose in Colo- This caused us to miss a large proportion of rado.Journal of Mammalogy 25:192- feeding data per day, which could account 193. for some of the variation. Grasses were also BEIDLEMAN, L. H., R. G. BEIDLEMAN, and B. slightly higher (3.4%) in fecal analysis than E. WILLARD.2000.Plants of Rocky direct observations. Consumption of grasses Mountain National Park. Falcon, Helena, and sedges is hard to observe because of their Montana, USA. low growth form, and bites were not recorded BELOVSKY, G. 1978. Diet optimization in a when species could not be identified, a factor generalist herbivore: the moose. Theoreti- which could also lead to differences between cal Population Biology 14:105-134. the two techniques. Wallmo et al. (1973) BUTLER, C. E.1986. Summer food utiliza- reported bite count methods estimated more tion and observations of a tame moose, use of shrubs as a class and less use of grass Alces aces.Canadian Field Naturalist and forbs than actually occurred for mule deer 100:85-88. (Odocodeus hemionus). CRETE, M. 1989. Approximation of K car- Fecal analysis could not differentiate rying capacity for moose in eastern willow, forb, or shrub species, and failed to Quebec. Canadian Journal of Zoology detect Populus tremuloides. Other species not 67:373-380. detected by fecal analysis included Cirsium DAVITT, B. B. 1979. Elk summer diet composi- spp., Rumex aquaticus, Senecio triangularis, tion and quality on the Colockum Multiple and Nuphar 'Idea ssp. Polysepala, but these Use Research Unit, Central Washington. species were less than 1 % ofthe observed diet. M.S. Thesis. Washington State University, Monthly fecal sample size was smaller than Pullman, Washington, USA. similar studies, which could have contributed JOYAL, R., and B. SCHERRER. 1978. Summer to not detecting these species. movement and feeding by moose in west- ern Quebec. Canadian Field Naturalist ACKNOWLEDGEMENTS 92:252-258. We want to acknowledge field technicians KNOWLTON, F. F.1960. Food habits, move- John Skinner, Basil Iannone, and Mandy ment, andpopulations ofmoose in Gravely Cluck who spent countless hours observing Mountains, Montana. Journal of Wildlife moose night and day. Park service staff were Management 24:162-170. more than helpful all 3 years of the study, KORFHAGE, R. C. 1974. Summer food habits with special thanks going to Ryan Monello. of elk in the Blue Mountains of north- Funding for this project was provided by eastern based on fecal analysis. Rocky Mountain National Park through the M.S. Thesis. Washington State University, USGS Idaho Cooperative Fish and Wildlife Pullman, Washington, USA. Research Unit. This manuscript is dedicated KREBS, C. J. 1999. Ecological Methodology. to the memory of Dr. Francis Singer. Second edition.Benjamin/Cummings, New York, New York, USA. REFERENCES KUFELD, R. C., and D. C. BOWDEN.1996. AUGUSTINE, D. J., and S. J. MCNAUGHTON. Movement and habitat selection of Shiras 1998. Ungulate effects on the functional moose (Alces aces shirasi) in Colorado. species composition of plant communi- Alces 32:85-99. ties: herbivore selectivity and plant tol- ,and S. F. STEINERT. 1990. An estimate erance. Journal of Wildlife Management of moose carrying capacity in willow

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