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Habitat Use by White-tailed Deer in a Tropical Forest SALVADOR MANDUJANO SONIA GALLINA GERARD0 SANCHEZ-ROJAS GLORIA ARCEO Depto. Ecologia y Comportamiento Animal, Instituto de Ecologia A.C., AP 63, Xalapa 91000, Veracruz, Mexico. GABRIELA SILVA-VILLILOBOS, CUCBA Universidad de Guadalajara, AP 39-82, Zapopan 451 10, Jalisco, Mexico Abstract: White-tailed deer in the tropical forest of "Chamela" in the state of Jalisco, Mexico, exhibit different spatial and temporal habitat use patterns. The heterogeneity of the understory of Chamela's tropical forest is determined by spatial (tropical dry forest and tropical semideciduous forest) and temporal (wet and dry seasons) variations in floristic composition, species richness and biomass, nutritional value, percentage of deciduous and evergreen species, and life form. During the wet season, white-tailed deer make greater use of the tropical deciduous forest. During this season the diet is less diverse. This greater selectivity in the diet is associated with an increase in foraging area, as greater distances are covered and the home-range is increased. In the dry period, low water and food availability is coupled with a decrease in cover to protect against climate and predators. White-tailed deer increases the diversity of its diet during this season. It also increases consumption of alternative food sources and water, such as fruits and flowers. Thus, habitat use is less selective in the dry season than in the wet season. Key words: Habitat structure, habitat use, Mexico, Odocoileus virginianus, tropical forest, white-tailed deer. INTRODUCTION White tailed deer (Odocoileus virginianus) are found throughout all of Mexico except on the Baja California peninsula and in northern Sonora (Hall 1981). The species inhabits a wide variety of vegetation types, such as temperate forests, grassland, semi-arid land, and tropical forest (Leopold 1965). This deer supplements the diet of local' ethnic groups (Mandujano and Rico-Gray 1991) and is 1 of Mexico's most important game species (Villarreal 1995). Most studies of this species have been carried out in temperate forests and semiarid zones of the United States, Canada, and Mexico (see Halls 1984). In contrast, few studies have been conducted in the tropical forests of Mexico, or in Central and South America (Vaughan and Rodriguez 1994). The present results are from a study of white-tailed deer (0. v. sinaloae) ecology in a tropical forest located in the state of Jalisco, Mexico, over a 6-year period (19891995). Our objectives were to determine basic life history information on population dynamics, activity patterns, and habitat use in a tropical environment noted for the marked seasonality of its available resources. The information contained in this paper is based on articles (Mandujano and Gallina 1993, 1995a, 19953, 1996; Mandujano et al. 1994; Mandujano and Martinez-Romero in press; Sanchez-Rojas et al. 1997), theses (Mandujano 1992, Sanchez-Rojas 1995, Silva-Villalobos 1996, PROCEEDINGS - 1997 DEERIELKWORKSHOP - ARIZONA Arceo 1997), and recent information which is yet to be published. See these publications for details regarding methods, statistical analyses, and results discussed in a wider context. We appreciate field support from R. E. Sanchez-Mantilla, L. E. Martinez-Romero, C. Lopez-Gonzalez, D. Valenzuela, G. Zavala, and G. Gonzalez. The following people collaborated in the identification of herbarium samples: F. Chiang (all groups), M. Sousa (Leguminosae), 0. Tellez (Leguminosae), and J. L. Vil'laseiior (Compositae). The following people collaborated in the laboratory analysis: L. Barrientos, M. Barrientos, M. Castellanos, G. Lopez, and L. Villarino. This study received support from CONACYT (P220CCOR-892 154, P020CCOR-903703 and 0327N9107) and SEP (DGICSA902467) projects. The UNAM's Chamela Biological Station provided all the facilities necessary for the successful completion of this study. DESCRIPTION OF HABITAT Study Site This study was carried out at the Universidad Nacional Autonoma de Mexico's "Chamela" Station for Research and Biological Diffusion, located on the coast of Jalisco. The Station covers an area of 3,200 ha. The elevation ranges from 30 to 580 m, although most of the territory is not higher than 150 m. The topography is irregular with numerous systems of small basins, all of which have seasonal run-off. The greatest quantity of water falls in September (Bullock 1986). Depending on the amount of rainfall, there is frequently no water in the streams by the end of the dry season. Apart from these seasonal streams, there are only 3 permanent rivers in a 100 km radius of the Biological Station. Climactic Pattern Average annual precipitation from 1977 to 1993 was 73.55 cm. Monthly precipitation causes 2 seasons: wet (rainy) and dry. The wet season, which lasts an average of 126 days, begins in June, with 80% of the annual rain falling between July and November (Bullock 1986). Twenty percent of the annual rain falls during the dry season, which lasts an average of 158 days. From June to July, the Trade Winds play a role in the variability of annual rainfall; cyclones occur during August to October and greatly increase the likelihood of winter precipitation (Garcia-Oliva et al. 1991). The mean annual temperature is 25 C, the hottest periods occurring between May and September (Bullock 1986). From June to November, the temperature was greater than 30 C on an average of 23 days (Mandujano and Gallina 1995a). From mid-December until mid-May, temperatures did not exceed 30 C. Insolation is highest in April. The maximum wind speed occurs from February to June and the minimum from August to December. The greatest evaporation occurs between March and June and the least between November and January. During the wet season dew was present for 7-15 days and between 5-12 days during the dry season (Gonzalez 1992). Types of Vegetation The dominant vegetation, covering 75% of the surface, is tropical deciduous forest (TDF). It is found on hills with shallow soils; the trees reach a height of 5 to 10 m and have a highly developed understory. Numerous tree and shrub species lose their leaves during the dry season (Lott et al. 1987). Some of the most common arboreal species are Cordia alliodora (Ruiz & Pav.) Oken, Croton pseudoniveus Lundell, Lonchocarpus lanceolatus Benth, and Caesalpinia eriostachys Benth. There is also tropical semi-evergreen forest (TSF), Habitat Use by White-tailed Deer in a Tropical Forest Mandujano et al. which grows along the principal streams in deep soils. The trees reach a height of 10 to 25 m. The most common tree species are Thouinidium decandrum (Humb. & Bonpl.) RadIk., Astronium graveolens Jacq., Brosimum alicastrum Sw, and Sideroxylon capiri A. DC. (Lott et al. 1987). Understory Structure In the wet and dry seasons during the period from 1989 to 1993, understory richness and biomass was measured in the TDF and TSF using permanent plots. The best represented families, genera, and species in the understory were Euphorbiaceae, Leguminosae, Sapindaceae, and Acanthaceae; Acalypha spp., Croton spp., Lasiacis ruscifolia, Coursetia caribaea, Dicliptera resupinata, Forchhammeriapallida, Capparis verrucosa, and Elytraria imbricata. In the TSF they were Euphobiaceae, Leguminosae, Bignoniaceae, Nyctaginaceae, and Sapindaceae; Acacia rosei, Guapira macrocarpa, Croton pseudoniveus, Thounidium decamdrum, Clytostoma binatum, Paullinia cururu, and Capparis verrucosa. During the wet season, 39% of the species were exclusive to the TDF, 43% to the TSF, and 18% are found in both vegetation types. Average species richness during the dry season was 2 species/m2in the TDF and 4 in the TSF; during the wet season, richness was 9 species/m2in the TDF and 8 in the TSF. Average biomass during the dry season was 7 g/m2in the TDF and 18 in the TSF, while in the wet season it was 41 g/m2 in both types of forest. There was a positive correlation between the precipitation and richness of both TDF and TSF and their biomass. Availability of Potential Food in the Dry Season Biomass availability for the species which deer consume in the TDF varied during the dry season from 2 to 12 g/m2, depending on the year. This corresponds to an average of 23% of the standing biomass in the understory of this vegetation type (Mandujano and Gallina 1995a). In the TSF, availability was estimated at 1 to 10 g/m2for species which the deer consume; this corresponds to an average of 9% of the biomass for this type of vegetation. Nutritional Value of the Vegetation Using a proximal analysis, we found that the nutritional value of vegetation was greater during the wet season, as there was a higher percentage of crude protein and nitrogen free extract (NFE). Nutritional value decreased during the dry season, when there was a higher percentage of crude fiber and total polypyenols (Silva-Villalobos 1996). Plants in the TSF have a higher percentage of fiber, less protein, and less NFE throughout the year. Plants in the TDF had a high nutritional value during the wet season and a low value during the dry season. Seasonal Fruit Production Fruit production of arboreal species tends to occur mainly from February to early April and from July to August (Bullock and Solis-Magallanes 1990). Some species deer consume during the dry season are Ficus sp., Brosimum alicastrum, Sideroxylon capiri, Opuntia excelsa, and Spondiaspurpurea. Characteristics of the Spondias purpurea Tree Fruits from the S. purpurea are an important source of water for the deer at the end of the dry season because there are few of water sources. S. pururea is a dioecious arboreal species. The density of adult trees is 7.5tha; approximately 50% are reproductive female trees, 38% of which Habitat Use by White-tailed Deer in a Tropical Forest Mandujano et al. produce more than 500 fruits (Mandujano et al. 1994). The average weight of fresh f i t is 7.5 g, and fruit production during 1991 was 14.9 kg/ha. Chachalaca (Ortalis poliocephala) foraging on S. purpurea has important consequences for the deer. When chachalacas forage, they drop many h i t s from their trees, making them available for the deer as well as for other terrestrial mammals. Exclusion experiments show that in the absence of this bird, the rate of S. purpurea fruitfall is very low (Mandujano and Martinez-Romero in press). Water Availability An estimate of the average availability of water for the deer was obtained using plant moisture content and the percentage of plants that the deer were known to consume in both types of forest during the dry seasons fiom 1990 to 1993. In the TDF, the average density of deer forage plants was 3 l h a (ranging from 10-56ha), while in the TSF the average was 28iha (ranging from 450ha) (Mandujano and Gallina 1995a). The average estimate of water in S. purpurea fruits was 10 Liha in 1991. HABITAT USE BY THE DEER Biological Cycle In the tropical forest of Chamela, the breeding season occurs between November and January (Mandujano 1992). Gestation occurs throughout the dry season, between December and June. The young are born between June and August. Group Size In this habitat, the white-tailed deer do not form large herds (Mandujano and Gallina 1996). Solitary individuals are frequently seen throughout the year. Females and their offspring comprise the most common social groups. Males are not known to form groups. This group size strategy is related to the availability of food, and to the density of cover in the understory that provides protection against predators. Population Dynamics Population density was estimated using a direct count of animals on line transects. Population density was estimated between 10 and 14 deer/km2(Mandujano and Gallina 1993, 1995b), and did not change over a 5year period. The birth rate is 1.5 fawns per female, however, the mortality rate is high from the fawn to yearling category. Mortality is higher for males than for females. We propose that the period between May and June is the "bottle-neck" for deer population increase in this tropical habitat. Feeding Habits Using microhistological fecal analyses, 129 species of 29 families were eaten by deer (Arceo 1997). The most important families were Euphorbiaceae, Leguminosae, and Convolvulaceae throughout the year, Malvaceae during the wet and transition seasons, and Anacardiaceae during the dry season. The deer selected 36,55, and 44 species during the wet, transition, and dry seasons, respectively. But on average, only 5 species represent 50% of the seasonal diet. Acalypha spp. was the most important food item in the wet and transition season. Overall, Acalypha langiana, Cardiospermum halicacabum, Coursetia caribaea, Croton sp., Abutilon sp., Spondias purpurea, and Ayenia micrata were the more important species in the diet. Deer diets became more diverse from wet to dry season, and the plant parts consumed changed in this period. Leaves and twigs were the most important plant parts in the annual diet, but in the dry season fruits and flowers, particularly fruits of red mombin (Spondias purpurea), constituted 30% of its diet. Overall, shrubs and vines were the Habitat Use by White-tailed Deer in a Tropical Forest Mandujano et al. most important life forms in the diet yearround, with trees being most important in the dry season. Perennial plants with deciduous leaves were dominant in the diet year-round. Plant species from TDF comprised a greater percentage of the diet, principally in the dry season, than those species from the TSF. Water Demand The deer population's need for water was estimated using the following factors: daily water demand for 1 individual, average weight, the percentage of each age group represented, annual population density, and consumption over 30 days at the end of each year's dry season (Mandujano and Gallina 1995~).Minimum and maximum individual demand was estimated at 1.9 and 3.9 Llday, respectively, for adult deer, 1.4 and 2.8Llday for young deer, and 0.8 and 1.7LIday for fawns. Use of Vegetation Types Through direct observations of deer and pellet group counts from 1989 to 1994, we found that the TDF is used more frequently throughout the year than the TSF. In particular, in the wet season the TDF is used more during the morning hours, while in the dry season it is used more in the afternoon. The TSF, in contrast, is used during the morning in the dry season and very little during the day in the wet season. Deer prefer the hillsides with northern exposure in the dry season. From 1992 to 1994, radiotelemetry of 1 male (n = 122 locations) and 1 female (n = 479) indicated that females preferred hillsides more than areas near streams (Shchez-Rojas 1995). Specifically, the doe favored hillsides facing NE or NW during the wet season and SW during the dry season. The male, on the other hand, made less use of hillsides facing NW and SE and preferred low areas. Activity Patterns The radiotracking of 2 deer provided the following data. In the dry season, the female exhibited more movement at dawn (0500-0800 hours) and at dusk (1700-2000 hours). In the wet season, she remained active throughout the day, slowing down notably at night (2 100-0400 hours). Male activity during the dry season was higher at dusk and at night. The distance covered by the female was 1.5 km/day in the dry season and from 2.5 km/day in the wet season. The male covered 2.5 km/day in the dry season of 1994. Estimates of female home-range were 11 ha during the dry season and between 24 and 44 ha in the wet season (Shchez-Rojas 1995). Figures for the male were 26 ha in the dry season of 1994. Predation At Chamela, the jaguar (Panthera onca), puma (Puma concolor), and ocelot (Leoparduspardalis) are the principal predators of white-tailed deer (LopezGonzalez et al. 1995). Like other studies (Main et al. 1996), it is very probable that the deer's habitat use is influenced by the risk of predation. Tracks of these felines are common along the streams of the study area. IMPLICATIONS Results indicate that the deer's foraging strategy during the wet season is to make greater use of the TDF because of its high nutritional value (higher percentage of protein and NFE and less fiber), greater richness and increased production of biomass of understory species as compared to the TSF. During this season the diet is less diverse, which indicates that the deer selects fewer species, principally those of the Euphorbiacea, Convolvulacea, and Leguminosae families, to cover its nutritional requirements. Deer get more energy and nutrients from these species, Habitat Use by White-tailed Deer in a Tropical Forest Mandujano et a/. thus permitting the accumulation of fat reserves for the mating season and for the critical dry season. This greater selectivity in the diet could be associated with an increase in the foraging area, as greater distances are covered and the home-range is increased. In the dry period, low water and food availability is coupled with a decrease in cover to protect against climate and predators. The deer's strategy is to select, .from low species richness and biomass, those plants and plant parts which are more nutritious and that have lower concentrations of fiber. Thus, the whitetailed deer increases the diversity of species and families in its diet during this season. It also increases consumption of alternative sources of nutrients and water, such as h i t s and flowers, especially Spondiaspurpurea, Ficus spp., and Brosimum alicastrum. Thus, habitat use is less selective in the dry season than in the wet season. Apparently, the distribution of fruiting trees plays a role here. During the dry season, deer show a clear preference for hillsides with northern exposure where the solar radiation is lower and humidity higher. Also, deer cover less distance, decreasing their home-range which could be a strategy to diminish energy demand and protect against predators. LITERATURE CITED Arceo, G. 1997. Habitos alimentarios del venado cola blanca en un bosque tropical caducifolio de Jalisco. M.S. Thesis, Universidad Nacional Aut6noma de MCxico, Mexico. Bullock, S. H. 1986. Climate of Chamela, Jalisco, and trends in south coastal region of Mexico. Archives for Metereology, Geophysics, and Bioclimatology 36:297-3 16. Bullock, S. H., and J. A. Solis-Magallanes. 1990. Phenology of canopy trees of a tropical deciduous forest in Mexico. Biotropica 22:22-35. Garcia-Oliva, F., E. Ezcurra, and L. Galicia. 1991. Pattern of rainfall distribution in the central Pacific coast of Mexico. Geografiska Annaler 73: 179-186. Gonzalez, M. G. 1992. Importancia ecologica del rocio en la selva baja caducifolia de Chamela, Jalisco. Bc. Thesis, Universidad Nacional Autonoma de Mexico, Mexico. Hall, E. R. 1981. The mammals of North America. Vol. 2. John Wiley & Sons, New York. 1 , 2 7 1 ~ ~ . Halls, L. K. 1984. White-tailed deer ecology and management. Stackpole Books, Harrisburg, PA. 870pp. Leopold, A. S. 1965. Fauna silvestre de Mexico. Institute Mexicano de Recursos Naturales Renovables. Mexico. 608pp. Lopez-Gonzalez, C., J. W. Laundre, K. Altendorf, and A. Gonzalez-Romero. 1995. Carnivores in a tropical dry forest of western Mexico: test of methods. Annual Meeting Northwest Scientific Association and Idaho Chapter, The Wildlife Society, Idaho Falls, ID. Lott, E. J., S. H. Bullock, and J. A. SolisMagallanes. 1987. Floristic diversity and structure of upland and arroyo forests in coastal Jalisco. Biotropica 19:228-235. Habitat Use by White-tailed Deer in a Tropical Forest Mandujano et al. Main, M. B., F. W. Weckerly, and V. C. Bleich. 1996. Sexual segregation in ungulates: new directions for research. Journal of Mammalogy 77:449-461. Mandujano, S. 1992. Estimaciones de la densidad poblacional del venado cola blanca (Odocoileus virginianus) en un bosque tropical caducifolio de Jalisco. M.S. Thesis, Universidad Nacional Autonoma de Mexico, Mexico. Mandujano, S., and S. Gallina. 1993. Estimaciones de la densidad del venado cola blanca basadas en conteos en transectos en un bosque tropical de Jalisco. Acta Zoologica Mexicana (nueva serie) 56: 1-37. Mandujano, S., and S. Gallina. 1995a. Disponibilidad de agua para el venado cola blanca en un bosque tropical caducifolio de MCxico. Vida Silvestre Neotropical4: 107-118. Mandujano, S., and S. Gallina. 19953. Comparison of deer censusing methods in tropical dry forest. Wildlife Society Bulletin 23: 180-186. Mandujano, S., and S. Gallina. 1996. Size and composition of white-tailed deer groups in a tropical dry forest in Mexico. Ethology, Ecology, and Evolution 8:255-263. Mandujano, S., and L. E. Martinez-Romero. In press. Fruit fall caused by chachalacas (Ortalis poliocephala) on red mombin trees ( S p d i a sspurpurea): impact on terrestrial h i t consumers, especially the white-tailed deer (Odocoileus virginianus). Studies on Neotropical Fauna & Environment 3 1. Mandujano, S., and V. Rico-Gray. 1991. Hunting, use, and knowledge of the biology of the white-tailed deer, Odocoileus virginianus (Hays), by the Maya of central Yucatan, Mexico. Journal of Ethnobiology 11: 175-183. Mandujano, S., S. Gallina, and S. H., Bullock. 1994. Frugivory and dispersal of Spondiaspurpurea (Anacardiaceae) in a tropical deciduous forest in Mexico. Revista de Biologia Tropical 42: 105112. Sanchez-Rojas, G. 1995. Ambito hogarefio y uso del habitat por el venado cola blanca en un bosque tropical caducifolio de Jalisco. M.S. Thesis, Universidad Nacional Autonoma de Mexico, Mexico. Sanchez-Rajas: G., S. Gallina, and S. Mandujano. 1997. Areas de actividad y uso del habitat de dos venados cola blanca (Odocoileus virginianus) en un bosque tropical de la costa Jalisco, Mexico. Acta Zool, Mex. (n.s.) 72:3954. Silva-Villalobos, G. 1996. Calidad del forraje para el venado cola blmca en el bosque tropical caducifolio de Charnels, Jalisco. Bc. Thesis, Universidad de Guadalajara, Mexico. Vaughan, C., and M. A. Rodriguez (eds.). 1994. Ecologia y manejo del venado cola blanca en Mexico y Costa Rica. EUNA, Heredia, Costa Rica. Villarreal, J. G. 1995. Venado cola blanca en Mexico. Revista DUMAC 17:29-34. Habitat Use by White-tailed Deer in a Tropical Forest Mandujano et al.