J. Range Manage. 46:467-492, November 1993 White-tailed deer and cattle diets at La Michilia, Durango, Mexico SONIA GALLINA The author is a research scientist on the Project Ecologia y Comportamiento Animalof the Institute de Ecologia, A. C. Apartado Postal, 63, C. P. 91000 Xalapa, Veracruz, Mexico. Abstract 2,250 to 2,850 m.a.s.1. The dominant species in the mixed oak-pine forest are the following: Quercus rugosa N&e, Q. sideroxyla H.&B., Fecal analysis was used to determine the relationships between Q. chihuahuensis Trel, Pinus engelmanni Martinez, P. chihua- white-tailed deer (Odocoiieus virginimus couesi [Cows and Yar- huana Engelm. and P. arizonicu Engelm. Chaparral and grass- row]) and cattle diets (Beef Master, Hereford and criollo), in lands are also present. The chaparral is characterized by Q. potos- Durango, Mexico. Deer preferred shrub and tree species (85% of ina Trel, Juniperus durangensis Martnez, P. lumholtzii Rob. et the diet), whereas cattle preferred grasses (61%). Although diets Fem. and Q. urbanii Trel. The grassland is an association of varied seasonally, as did forage availability and quality, the same Muhlenbergia rigida [H.B.K.] Kunth, M. montnna [Nutt] Hitch, selective forage pattern was maintained throughout the year. There Bouteloua gracilis [H.B.K.] Lag and Aristida schiedeana Trin. et was a significant difference in the use of different plant groups Rapr. (Gallina 1981). There are 2 well-defined seasons: the dry between the 2 herbivores. The diet overlap index (50.51%) sug season from February to May and the rainy season from June to gested competition during the wet season, but forage was abundant September. Light winter rains occur in December and January, (628 kg/ha dry weight biomass compared with 380 kg/ha in the dry providing less than 5% of the total annual precipitation, and occa- season), thus reducing potential conflicts. Deer and cattle can sionally it snows (Gallina 1981). The climate varies between semi- simultaneously forage in this area without detriment to either arid temperate and subhumid temperate (Garcia 1964). The species. The vegetation can maintain a stable composition under temperature fluctuates between 17.4” C and 20.7O C. The mean higher utilization levels when used by 2 herbivores with different annual precipitation is 609 mm at meteorological stations Mezqui- forage patterns than when used by only 1 herbivore. tal and Chalchihuites (1963-1975). The records from 1980-1985 at Key Words: deer, Odocoileus virginianus couesi, cattle, Michilia La Michilia show annual precipitation of 600 to 860 mm. Biosphere Reserve, Durango, diets, microhistological techniques, biomass Materials and Methods Deer and cattle diets have been studied extensively, and infor- In 1975, plant material and deer fecal samples were collected mation on diet overlap and potential competition is necessary to during April (3 mixed fecal samples that consist of a pellet of each adjust habitat management at the local level. This is particularly fresh group collected), May (12), August (6), late September and important in a Biosphere Reserve where the main economical October (13), and November-December (13), at the La Michilia activity is cattle management. Our objectives in this study were to Biosphere Reserve. A total of 47 mixed fecal samples were ana- determine deer and cattle diets, intensity of competition for food, lyzed (Gallina et al. 198 1). In 1980-198 1, the collection methodol- seasonal changes, dietary similarity and overlap at the La Michilia ogy was changed by Morales (1985), and the pellets collected were Biosphere Reserve, Durango, Mexico. Forage availability and counted. A total of 866 pellets of individual deer fecal groups were utilization were also determined to clarify resource use in a mixed collected [June (140), August (118), November (336), January oak-pine forest. (225) and May (47)]; as were 751 individual cattle fecal samples: The microhistological analyses of fecal samples has been used June (116), August (99), November (153), June (215), May (104), extensively to determine herbivore diets (Storr 1961, Sparks and July (64) in order to quantitatively compare both diets (Morales Malechek 1968, Zyznar and Urness 1969, Ward 1970, Todd and 1985). Hansen 1973, Anthony and Smith 1974, Goodwin 1975, Holechek The identification of the botanical composition of the diet was et al. 1982, and Elliott and Tanner 1985). Although not without based on the fecal analysis by microhistological techniques (100 flaws, the technique has proven to be reasonably reliable for study- fields for each mixed sample). Five slides of 8 different collecting ing herbivore diets (Holechek et al. 1982). areas were made on each sampling occasion, and 20 fields on each slide were examined. A total of 4,700 fields were examined in 1975, Study Area and 6,800 fields in 1980-81. Epidermal identification requires ref- This study was carried out at the La Michilia Biosphere Reserve, erence slides of plant material; these were made and studied, prior which is located in the southeast of the State of Durango, Mexico, to fecal analysis, by 3 observers in 1975 and 1 observer in 1980-8 1. between 23’ 30’ and 23O 25’ N Lat and 104’ 21’ and 104’ 15’ W Frequency of each species identified in each location (micros- Long. The Reserve is located on the foothills of the Sierra Madre copic field using 100 power magnification) was recorded. Percen- Occidental, 145 km south of Durango. The altitude varies from tages were converted to density using a table developed by Fracker and Brischle (Sparks and Malechek 1968), and the relative density, This research was funded in part by the Consejo National de Ciencia y Tecnologia expressed as a percentage of each species in the sample, was calcu- de M&&o. Manuscript accepted 15 May 1993. lated. Relative density was used to estimate the percentage dry weight of the species in the sample. The epidermal material not JOURNAL OF RANGE MANAGEMENT 46(6), November 1993 487 identified constituted 5% on deer fecal samples and 20% on cattle WHITE-TAILED DEER fecal samples. The diets of the 2 ruminants (deer and cattle), between deer diet in different years (1975 and 1980-81) and their seasonal variation were compared using a 3 way ANOVA (Sokal and Rohlf 1969) to see if observed foraging patterns were affected by changing conditions. In this paper the diet similarity was analyzed using the Sorensen Index S=2a where 2a+b+c a = number of plant species used by both herbivores b = number of plant species consumed by deer c = number of plant species consumed by cattle Diet overlap was obtained by Pianka’s formula (1975), where pg and p& are the proportions of i resources used by the j ojr = okj q g;; zp2n species.(deer) and the k species (cattle). CA-ITLE The availability of forage was obtained with the Pechanec and Pickford method (1937). A double sample technique was used in the same areas where the fecal samples were collected from 1978 to 1980, in 14 transects with 10 sample areas of 1 rnz separated by 40 m. Available aerial biomass to a height of 1.8 m was estimated during the wet season, i.e., November 1978, October 1979, October 1980 (n = 420) when biomass values are highest, as well as during the dry season, May 1979, June 1980 (n = 280) when biomass is lowest (Gallina 1990). During the biomass estimation the percent of the resource used in the field by herbivores was also determined. Results and Discussion -(61 .O%) Global Diets Shrub and tree species constituted more than 85% of the annual diet of white-tailed deer. Gramineous species were the most impor- tant food in cattle diets, (>60%; Fig. 1). These results are sup- ported by those of other studies reported by Van Dyne et al. (1980). The total number of plant species consumed by deer was 135 in 1975 (Gallina et al. 1978) and 99 in 1980-1981 (Morales 1985). However, in general, the deer depend on few shrub and tree species. For deer, the most important of these species were: mistletoe GRASSES FORBS SHRUBS TREES (Phoradendron bolleanum [Seem] Eichl and P. villosum Nutt), oak Fig. 1. Annual diets of white-tailed deer and cattle showing the different (&ercus spp.), juniper (Juniperus deppeana Martinez and J. foraging patterns. durangensis Martinez), and madrone (Arbutus spp. and Artosta- phylos spp.). These species represented the highest percentage of deer diet in both studies (Table 1). There were significant differences in (i) the use of the different Cattle consume 84 species (Morales 1985), and of these more plant groups by each herbivore (F q 79.361, P<.OOl) and (ii) in the than 50% are gramineous (46 species). This indicates a high selec- preferences for the different plant groups by both herbivores (F q tivity for grasses at La Michilia, mainly of the genera Muhlenber- gia (22% of the diet) and Aristida (Table 2). Holechek et al. (1982b) 35.551, P<.OOl; 3 way ANOVA). During the dry season, cattle consumption of tree species reported that cattle grass consumption ranged from a low of 54% in increases, perhaps as a strategy for complementing their diet when late spring of 1978 to 91% in the fall of 1977. Many investigators other forage is scarce. The same pattern occurs in other regions, as have reported grasses to be the most important component of has been shown by Holechek et al. (1982b). In spite of this, the cattle diet (see Van Dyne et al. 1980). Beck (1975, cited by Hole- basic diet of cattle is grass (more than 50%). The same pattern is chek et al. 1982b) reported that plant phenology was the primary observed for deer with respect to shrub species.