Structure of Collared Peccary Herds in South Texas: Spatial and Temporal Dispersion of Herd Members

Abstract

The collared peccary (Tayassu tajacu) is regarded as a social ungulate that lives in a stable, cohesive herd throughout its life (Bigler, 1974; Ellisor, 1976; Ellisor and Harwell, 1969, 1979; Sowls, 1974). Collared peccary herds are described as essentially closed social units (Byers and Bekoff, 1981) with stable territories (Bissonette, 1976, 1982a, 1982b; Day, 1977; Schweinsburg, 1969, 1971) and little exchange of members between herds (Bissonette, 1976, 1982a, 1982b; Ellisor, 1976; Ellisor and Harwell, 1969, 1979; Schweinsburg, 1969, 1971; Schweinsburg and Sowls, 1972). Day (1977) reported that only about 11% of the members of observed herds migrated into other herds. However, previous studies have mentioned that members of collared peccary herds separate from the main group (Bigler, 1974; Bissonette, 1976, 1982a, 1982b; Byers, 1980; Day, 1977; Foldesh, 1982; Green et al., 1984; Jennings and Harris, 1953; Kiltie, 1980; Neal, 1959; Schweinsburg, 1969, 1971; Supplee, 1981) and that periods of separation may last as long as 2 weeks (Byers, 1980; Bissonette, 1976, 1982a, 1982b). In Arizona, members of larger herds have been reported to separate more frequently than members of smaller herds (Day, 1977), and in Texas, separation of members from the herd has been reported to be most frequent during spring and summer (Bissonette, 1976, 1982a; Jennings and Harris, 1953). However, detailed information on the spatial and temporal dynamics of grouping behavior within peccary herds is not available. The present study examines the structure of collared peccary herds in south Texas in terms of spatial and temporal patterns of dispersion among herd members. We were particularly interested in documenting the extent to which single individuals or subgroups separated from the main group, and in relating occurrence of such separation to sex, age, time of day, and season. The study was conducted on the 6,151-ha Chaparral Wildlife Management Area, located in Dimmit and LaSalle counties in south Texas. Vegetation on the study area was mesquite (Prosopis glandulosa)-dominated, mixed brush, typical of much of south Texas. Peccaries from two adjacent herds (Herd A and Herd B) were marked and recaptured from July 1981 through October 1982. Captured animals were tagged in both ears, sexed, and examined for dental wear to determine wear class (wc) (Sowls, 1961). Members from Herd A had been marked and observed previously by Ellisor (1976) and Green et al. (1984). Peccaries in wc 1 were assumed to range in age from 1-3 years; wc 2, 2-5 years; wc 3, 3-7 years; wc 4, 5-14 years; and wc 5, 7-14 years (Low, 1970). Adult peccaries were fitted with radio collars (weight, 310-350 g). During subsequent recaptures the condition of the radio collar and the animal were noted. Radio-collared peccaries were radio tracked for 2 to 4 complete 24-h tracking days during each month from December 1981 through December 1982. Peccaries were monitored simultaneously by two radio trackers taking bearings from two of the three Yagi antenna towers that formed an equilaterial triangle (0.8 km on a side) positioned within territories of the two herds monitored. The sequence in which individuals were sampled within each hour was determined randomly without replacement. An attempt was made to record a bearing on each radio-collared individual at least once and if possible twice every 2 h. A 2-h interval is defined here as two successive radio-tracking hours. Each 24-h radio-tracking day was divided into 12 2-h intervals. Radio tracking during most of the 24-h tracking days was continuous for 24 h with the exception of June, July, and August when half of the 24-h tracking days were divided into four 6-h periods spread over 2 to 3 days. These two types of data were pooled, except when determining duration of separation of individuals from the main group, when only complete 24-h tracking days were used.