Desert bighorn sheep in Mexico

Abstract

The management of bighorn sheep in Mexico is not based on empirical data. We conducted phone interviews and a literature review to determine published information on desert bighorn sheep in Mexico. Most information on bighorn sheep was published prior to 1983 and focused on population size and structure. We concluded that desert bighorn sheep in Mexico are in need of further research. To provide better management to bighorn sheep, research needs to focus on basic life history strategies (e.g., minimum viable population size, diet, habitat relationships, movements, predation, diseases, and metapopulation dynamics). Bighorn sheep in Mexico have been scarcely studied. We conducted a habitat use study in Rancho el Plomito, Sonora, Mexico from April 1997 to December 1998 and the data were used to determine causes of sexual segregation. Vegetation associations were not used according to their availability. Segregated females formed larger groups, were closer to escape terrain and occupied more rugged areas than males. Sexual segregation exhibited by desert bighorn sheep in Rancho el Plomito may result from different energetic and reproductive strategies for males and females. Females tend to optimize conditions suitable for rearing offspring and males maximize body condition. Bighorn sheep in Mexico are important game animals and are confined to scattered populations (Villa 1.959). Little research has been conducted on desert bighorn sheep and consequently the species is listed in appendix II of CITES (i.e., vulnerable) (Valdez 1997). Tarangb and Krausman (1997) emphasized food selection as a fundamental research topic for the species in Mexico. We conducted a study of diet composition in Sonora, Mexico from April 1997 to December 1998. We identified 41 plant species consumed by desert bighorn sheep. The mean annual diet was composed of browse, forbs, succulents, and grasses. Composition of forage categories in diets of males and females was similar. The coefficient of overlap (Morisita 1959) of diets of male and female bighorns for seasons indicated significant overlap. Sexual segregation of desert bighorn sheep in Sonora, Mexico was not related to forage selection (i.e., botanical composition, forage quality), and suggested that other factors (i.e., physiographic characteristics) were responsible for this segregation.