Aspects of Barbary sheep (Ammotragus lervia) biology in Palo Duro Canyon, Texas
Gray, Gary Gene
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Forty-four Barbary sheep (Ammotragus lervia) were introduced into Palo Duro Canyon in 1957-58. This study was conducted 1) to collate the published literature on Barbary sheep, 2) to provide some basic biological data on the Palo Duro Canyon population in the original release area, and 3) to suggest how these data can be applied to species management. Two methodologies were developed for determining age and/or sex. One involved defining nine age-sex classes based upon combinations of sexually dimorphic characteristics, and age-related variation in body size, horn size, and morphological configuration. This was used to assign Barbary sheep to age-sex classes from field observations. The other method substantiated the use of horn growth checks to estimate age in this species, and provided regression equations for estimating age from horn length. Regression equations were also developed to estimate weight from horn length. This is the first study in which horn size has been used as a weight estimator. Population statistics were estimated from 1,246 hours of observation on 271 field days from February 1977 through January 1979. Observations were made from a vehicular blind on the canyon rim, from fixed points on a standard observation route hiked each field day, and during seven helicopter censuses of the Dry Creek branch (65 km^2) of Palo Duro Canyon. The findings 1) suggested population densities of 0.8 - 3.6 Barbary sheep per km , 2) indicated that about 7 0 percent of births take place in March and April, but that some parturition is distributed throughout much of the year, 3) showed a natality rate of about 48 juveniles: 100 females, 4) disclosed an adult sex ratio of 40 males: 100 females, and 5) implied that juveniles and subadults comprise about 30 percent of the population, adult males 20 percent, and adult females 50 percent. The survival ratejfrom birth to one-year of age approximates 35 percent, is about 77 percent per year for males from one to 3.5 years of age, and is estimated to average 55 percent per year for males from 3.5 to 10.5 years of age. The topographic distribution of 529 sightings indicated that Barbary sheep range over all levels in Palo Duro Canyon, but spatial utilization is concentrated on precipitous bluffs which form the canyon walls. Diet studies showed that Barbary sheep are predominately browsers, but consume appreciable amounts of plants from the other forage categories in all seasons. The most important food plants were sand shinnery oak (Quercus havardii), mountain mahogany (Cercocarpus montanus), bladderpods (Lesquerella spp.), and blue grama (Bouteloua gracilis). Barbary sheep were infected with three species of gastrointestinal helminths (Monezia expansa, Skrjabinema caprae, and Haemonchus contortus). Ectoparasites found included the ticks Dermacentor albipictus and Otobius megnini, and the lice Bovicola fulva and B. neglecta. B. fulva is a new species. Elaeophorosis was also documented in Barbary sheep for the first time, and many animals exhibited crusty lesions or healed scars about the head as a result of infection by Elaeophora schneideri. Social organization is characterized by female group leadership and group dynamics (size and composition) which is highly variable within a basic pattern reflecting species phenology. Five types of intraspecific aggressive behavior and six vocalization types were described, and social ontogeny was delineated. Several adaptive features of Barbary sheep biology were described and discussed, and a number of considerations relevant to species management were presented. The high degree of variability associated with each aspect of Barbary sheep biology reviewed or studied suggests that this species may be able to adopt a colonial (r) or equilibrium (K) strategy depending upon population density and habitat conditions.