THE SoUTHWESTERN NATURALIST 44(2):199-204 jUNE 1999

VARIATION IN HERD SIZE OF COLLARED PECCARIES IN A MEXICANTROPICAL FOREST

SALVADOR MANDUjANO

Departamento de Ecología y Comportamiento Animal, Instituto de Ecología A. C., APartado Postal 63, Xalapa,CP 91000, Veraauz, México. email: mandujan@ecologia.edu.mx

ABSTRAcr-Collared peccaries (Pecan tajacu sonorensis) inhabit the tropical deciduous and semi-deciduous forests of Charnela Biological Station on the coast of Jalisco, located in the southern-most pan of the geographical distribution of this subspecies. These vegetative communities aredifIerent in fIoristic composition, phenology, aerial biomass, productivity, nutritive value, and rootbiomass. From 1989 to 1994, I analyzed the variation of herd size of collared peccaries in relationto seasonal and spatial variation of food, cover, water, and predation risk. Nl,1mber of individualsper herd ranged from 1 to 12, with groups of 1 to 4 individuals being the most common. Intropical semi-deciduous forest pec{;aries usually formed large herds, but in tropical deciduousforest they most commonly formed small herds. Number of individuals per herd was similar duringrainy and dry seasons. Collared peccaries subdivided into small groups to forage in tropical de-ciduous forest, and aggregated into herds in semi-deciduous tropical forest. Density and herd sizeof P. t. sonorensis in Charnela were more similar to those found in other tropical forests than thosein northern arid habitats. Peccaries consumed a high percentage of roots thorough the year. Fromrainy to dry seasons consumption of low quality roots increased as high quality leaves-branchesdecreased. During the dry season, variation in fruit production and rate of fruit fall supportdifIerent herd sizes.

RESUMEN-El pecari de collar (Pecan tajacu sonorensis) habita en los bosques tropicales caduci-folios y subperennifolios de la Estación Biológica "Chamela" en la costa de Jalisco, localizada enla parte más sureña de la distribución geográfica de esta surespecie. Estas comunidades vegetativasson diferentes en su composición flonstica, fenología, biomasa aérea, productividad, valor nutri-tivo y biomasa de raíz. Se analiza la variación del tamaño de las manadas del pecari de collar enrelación a los cambios estacionales y espaciales del alimento, cobertura, agua y riesgo de depre-dación durante el período 1989 a 1994. El número de individuos por manada varió de 1 a 12,siendo los grupos de 1 a 4 individuos los más comunes. En el bosque tropical subeperennifoliolos pecaries formaban manadas grandes, mientras que en el caducifolio comunmente formabanmanadas pequeñas. El número de individuos por manada fue similar entre las épocas de lluvia yla seca. El pecarí de collar se dividió en pequeños grupos para pastar en el bosque tropicalcaducifolio, y se reunieron en manadas en el bosque tropical subperennifolio. En Charnela, laabundancia y el tamaño de las manadas de P. t. sonorensis fueron más similares a lo encontradoen otros bosques tropicales que lo reportado para zonas áridas norteñas. Los pecaries consumenaltos porcentajes de raíces durante todo el año. De la época de lluvias a la época seca, el consumode raíces de baja calidad se incrementó mientras que disminuyó el consumo de hojas y ramas dealta calidad. Durante la época seca la variación en la producción de frutos y la tasa de caída defrutos, sostienen manadas de diferente tamaño. .

México (Ceballos ~d Miranda, 1986). Duringa study of white-tailed deer (Odocoileus virgini-anus) in fue aTea (Mandujano and Gallina,1995a, 1995b), 1 algO gathered data on fue col-lared peccary. The objective of this study wasto analyze fue variation of herd size in relationto seasonal and spatial variation of food, cover,

The collared peccary (Pecan tajacu sonoren-sis) has been studied extensively in the aridzones of Arizona and New Mexico (Sowls,1984). In contrast, there has been little re-search on this subspecies in tropical habitats.The collared peccary is resident of tropical for-ests near Ch~ela in southwestern Jalisco,

200 The Southwestern Naturalist vol. 44, no. 2

and water in fue tropical forest located in fuesouthernmost part of fue geographical distri-bution of P. t. sonorensis (Hall, 1981).

METHOOS ANO MATERIALS-This study was con-ducted in fue Charnela Biological Station on fuesouthern Pacific coast of jalisco. The station covers3,200 ha with elevations ranging from 30 to 500 m.Mean annual temperature and precipitation are25°C and 748 mm (SD = 119 mm), respectively.

Eighty percent ofthe raiD falls betweenjuly and Oc-tober, fue dry season lasts from November to june(Bullock, 1986). Dominant vegetation is tropical de-ciduous forest located on bilIs. Tree heights wryfrom 4 to 15 m and there is a well-developed under-story (Lott et al., 1987). The station also has semi-deciduous forest along large streams, with treesranging from 10 to 25 m in height.

For each sample month, five to eight transectswere located along existing roads. Though place-ment of transects should be random (Burnham etal., 1980), dense understory at the Charnela sta-tion prevented placement of long random tran-sects. Therefore, 1 used existing dirt roads. Totaltransect length varied from 6 to 11 km (X = 9.1km) each month. Length of these transects wasproporcional to fue afea of each vegetation type,74% crossed tropical deciduous forest, the restcrossed tropical semi-deciduous forest. 1 walkedalong transects at 1 to 2 km per hour from 0700h to ,1200 h and 1600 h to 2000 h, two to fourtimes per month. AlI observations were madefrom O to 30 m into the forest, perpendicular tothe transect. Fieldwork was done in the rainy sea-son from 1989 to 1993 and the dry season from1990 to 1994. The observation rate was defined asthe number of herds observed per kilometer oftransect covered. This rate was calculated by sea-son using data from all years; the nonparametricMann-Whitney U-test was used to see differencesbetween seasons (Sokal and Rohlf, 1995). The dis-tribution of the number of individuals in smallherds (1-4 peccaries per herd) or large herds (>5peccaries per herd) by season (rainy and dry) andvegetation type (tropical deciduous forest andtropical semi-deciduous forest) , were comparedby Chi-square Goodness of Fit tests. The strip tran-sect method was employed to estimate annualdensity (D) of herds per km2. The formula appliedwas D = ni L2w, where n is the number of herds

observed, L is the totallength of the transect, andw is one half of the total transect width (w = 0.03km in this study). Once herd density was obtained,the number of individuals per km2 was estimatedby multiplying herd density by average herd sizein this afea. Results are expressed as a X :t 1 Sr.'.

RESULTS AND DISCUSSION-A total of 44 herdswas observed along fue 816 km walked in Cha-mela. Due to fue dense vegetation cover, Icould not count fue numbe~ of individuals in10 of fue herds. In fue remaining 34, a total of139 individuals was seen. AlI individuals prob-ably were not counted, because sightings typi-cally occur at road crossings and some individ-uals mar have already gone by. Herd observa-tion Tales were similar between rainy (0.071 :!:0.04 herds per km) and dry seasons (0.078 :!:0.06) (Mann-Whitney U-test, U= 12, P= 0.84).The number of individuals per herd rangedfrom 1 to 12, with groups of 1 to 4 individualsbeing fue most common (Fig. 1). In fue trop-ical semi-deciduous forest, peccaries usuallyformed large herds (5-12 individuals perherd), whereas in fue tropical deciduous forestthey most commonly formed small herds (1-4individuals per herd-}(I. = 4.6, di = 1, P =0.03). The number ofindividuals ofboth smalland large herds were similar during fue rainyand dry seasons (}(I. = 0.002, df= 1, P = 0.66).Independent of season, average herd size intropical deciduous forest was 3.3 :!: 0.6 individ-uals per herd, and 4.5 :!: 0.6 in tropical semi-deciduous forest. In contrast, independent offorest type, average size of herd during fuerainy season was 3.9 :!: 0.6, and 4.4 :!: 0.7 infue dry season. Density of herds per year variedfrom 0.3 to 2.5 herds per km2 depending onfue year, with an average of 1.2 :!: 0.9 herds perkm2. Average density of individuals was 4.9 :!:1.6 peccaries per km2.

Density and herd size of P. t. sonorensis inCharnela were more similar to those found inother tropical forests than those in northernarid habitats. In Peru, Kiltie and Terborgh(1983) estimated a density of 1.2 herds perkm2; in Panarna, Eisenberg and Thorington(1973) calculated 7 individuals per km2. Insome forests in Venezuela, Panarna and Peru,47%, 75%, and 87% of fue herds, respectively,were made up of 1 to 4 individuals (Kiltie andTerborgh, 1983; Robinson and Eisenberg,1985). In contrast, in Arizona, mean popula-tion density was estimated as 11.8 :!: 4.4 pec-caries per km2, average herd size fluctuated be-tween seven and 16 animals, and maximumherd size varied from 20 to 30 peccaries (Sowls,1984). Therefore, population density and herdsize of this subspecies in fue Charnela region

june 1999 Mandujano-CoIlared peccaries in a tropical forest 201

16

14

12>-()cQ) 10:JO-Q).::: 8Q)

:J-O 6CJ)

..cro

4

2

o1-2 3-4 9-10 11-125-6 7-8

number of animals / herd

FIG. 1.-Frequency of fue nurnber of individuals per herd in two types of tropical forest near Charnela,jalisco, Mexico.

in fue tropical deciduous forest throughoutfue year. Aggregation of herbivores is expectedto increase in habitats with substantial variationin forage quality and productivity, and signifi-cant predation (Fryxell, 1991). Vegetative com-munities in tropical semi-deciduous forest andtropical deciduous forest are different in theirfloristic composition (Lott et al., 1987), phe-nology (Bullock and Solis-Magallanes, 1990),aerial biomass (Martínez-Yrizar et al., 1992),productivity (Martínez-Yrizar et al., 1996), nu-tritive value (Silva-Villalobos, 1996), and rootbiomass (Castellanos et al., 1991). During fuerainy season, species richness in the understoryis higher in tropical deciduous forest than intropical semi-deciduous forest, but net foliageproduction (NFP) is similar between fuese veg-etation types (S. Mandujano and S. Gallina, inlitt.); and fue quality (protein : fibre index) oísome species is higher in tropical deciduousforest than in tropical semi-deciduous forest(Silva-Villalobos, 1996). During fue dry seasonspecies richness and NFP are higher in tropicalsemi-deciduous forest than in tropical decidu-ous forest, and quality is low and similar inboth vegetative comunities. In addition, there

depends more on habitat features than on tax-onomic affinity.

Th'e continuous observations and mappingof two particular herds suggest that subdivisionof a herd into small groups occurs in Charnela.This pattern has been reported in other trop-ical forests (Castellanos, 1983; Robinson andEisenberg, 1985) and brushland in Texas(Green et al., 1984), where a herd ofcollaredpeccaries subdivided into small groups in areaswith few resources. In contrast, fue en tire herdand sometimes aggregations of distinct herds,occurred at sites of abundant food (Green etal., 1984). During fue entire year, herds com-monly comprised juvenile and adult individu-als in fue tropical semi-deciduous forest;whereas

in fue tropical deciduous forest it wasmore common to see groups of one to fouradults and juveniles foraging together. New-born peccaries were seen only in tropical semi-deciduous forest during October and Novem-ber, but there is not enough data to test if pec-caries prefer fue semi-deciduous forest for

rearing young.Collared peccaries form large herds in fue

tropical semi-deciduous forest and small ones

The SouthUle5tem Naturalist vol. 44, no. 2202

hillsides in tropical deciduous forest, althoughat low densities with limited fruit production(Lott et al., 1987; Mandujano et al., 1994).Consumption of Spondias fruits by peccariesdepends on fue foraging activity of Chachala-cas (Ortalis poliocephala), because this birdknocks fue fruits to fue ground, making themavailable to peccaries (Mandujano and Martí-nez-Romero, 1997). A similar association hasbeen observed between herds of collared pec-caries and troops of monkeys foraging in trees(Robinson and Eisenberg, 1985). Large herdswere observed eating fruits of Ficus and Brosi-mum trees. Relative abundance of fuese speciesof trees is high in fue tropical semi-deciduousforest (Lott et al., 1987). Therefore, high fruitproduction and high rate of fruit fall of sometree species in the tropical- semi-deciduous for-est could support large herds.

Predators such as jaguar (Panthera onca),puma (Puma concolor), ocelot (Leopardus par-dallis), coyote (Canis latrans--Ceballos and Mi-randa, 1986) and recentIy bobcat (Lynx rufus--López-González et al., 1998), inhabit Charnela.Particularly, fue jaguar and puma include pec-caries in their diet (R Nuñez and B. Miller, inlitt.). In other tropical forests, jaguar is one offue principal predators of peccaries (Aran da,1994). Social organization and size of herds oflarge herbivores are influenced also by preda-tion risk (Hirth, 1977; Nelson and Mech, 1981;Fryxell, 1995). Thus, small herds and solitaryindividuals are more frequent in forested hab-itats, whereas in oren areas, herds tend to belarger (Mandujano and Gallina, 1996). In fueCharnela region, fue jaguar and puma use fuetropical semi-deciduous forest as pathways intheir daily activities (R. Nuñez, B. Miller, andF. Lindzey, in litt.). Thus, when peccaries arein the tropical semi-deciduous forest a partic-ular individual' s chances of being killed byfuese cats might be lessened by being part ofa large herd. Spatial and temporal variation infood and cover resources, and predation risk,seem to be fue principal factors determiningvariation in herd size of collared peccaries atCharnela.

are no sources of free water during fue dryseason (Mandujano and Gallina, 1995b) .Therefore, fue potential of this tropical forestto support different herd sizes varies spatially(tropical deciduous forest versus tropical semi-deciduous forest) and seasonally (rainy versusdry). Overall, tropical semi-deciduous forestsupports larger herds of collared peccaries.

Diet of collared peccaries in Charnela con-sisted of 46% and 50% roots, 43% and 39%leaves-branches, and 10% and 11 % fruits dur-ing fue rainy and dry seasons, respectively(Martínez-Romero and Mandujano, 1995).Particularly, monthly consumption of rootsand leaves-branches were inversely correlated(r = -0.93, df= 4, F = 23.8, P = 0.008): moreroots were consumed in fue dry season, andmore leaves-branches in fue rainy season. Sim-ilar patterns of consumption were reported inother tropical deciduous forests (McCoy et al.,1990; Olmos, 1993), wherein consumption oflow quality roots increased as high qualityleaves and fruits decreased. Olmos (1993) pro-posed that variability in percentage of rootsand tubers in fue diet is fue result of pro-nounced seasonality of tropical deciduous for-esto In Charnela, availability of leaves is highonly during fue rainy season; whereas through-outthe year, total root biomass is high (Kum-merów et al., 1990). Despite fue great root bio-mass, fue cost of foraging mar be high becausepeccaries must search and scratch for roots ata depth of 0-10 cm (Olmos, 1993). Foragingfor roots in small herds or groups could be aoptimal strategy because fue quantity of rootsof specific plants consumed by peccaries in alocalized area probably is not enough to sup-port a large herd.

During fue dry season, collared peccariesconsume fruits of some species like opuntia ex-celsa, Ficus, Brosimum alicastrum, Spondias pur-purea, and unidentified legumes (Martínez-Romero and Mandujano, 1995). In arid habi-tats and other tropical deciduous forests, den-sity, herd size, borne range, and movementsdepend on abundance of certain forage spe-cies, mainly opuntia in arid habitats and spe-cies of fruit trees in tropical forest (Bissonette,1985; Robinson and Eisenberg, 1985; McCoyetal., 1990). In Charnela I commonly observedsmall groups of peccaries, feeding signs, andtracks below opuntia and Spondias trees. Thegreatest number of fuese trees are found on

L. E. Martínez-Romero and A. Hernández gaveme information from their field observations oncollared peccaries in the study area. 1 thank M.Aranda, A. González-Romero, P. A. Jansen, and B.E. Coblentz for their comments and suggestions

June 1999 Mandujano,-CoIlared peccaries in a tropical forest 203

regarding an early version of this rnanuscript. Thisresearch was supported by the Charnela BiologicalStation. The study was also enhanced by a sirnul-taneous study of the white-tailed deer financed byCONACYT (P220CCOR-892154, PO20CCOR-903703

y 0327N9107).

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Submitted 9 june 1997. Accepted 24 November 1998.Associate Editor was Mari¡ D. Engstrom.