CAUSE SPECIFIC MORTALITY OF DESERT BIGHORN SHEEP LAMBS IN THE FRA CRISTOBAL MOUNTAINS, NEW MEXICO, USA

• Main Author: Parsons, Zachary David
• Format: Thesis
• Language: unknown
• Published: University of Montana 2007
• Subjects: Aquila chrysaetos; cougar; desert bighorn sheep; eagle; lamb; mortality; New Mexico; Ovis canadensis mexicana; Puma concolor; golden eagle
• Online Access: https://scholarworks.umt.edu/etd/173; https://scholarworks.umt.edu/context/etd/article/1192/viewcontent/Parsons_Zachary_Thesis_071215.pdf

Desert bighorn sheep (Ovis canadensis mexicana) are an endangered species in New Mexico. Many of the small, isolated populations of desert bighorn are declining, and factors affecting their growth rates include low lamb recruitment and high mortality of adults due to cougar predation. No one has previously reported cause-specific mortality rates for desert bighorn lambs. My objectives were to determine the causes, extent, and timing of lamb mortality in the Fra Cristobal Mountains, New Mexico, USA. I tested 3 capture techniques during 2001 and 2002: approaching lambs on foot and restraining them by hand; jumping from a helicopter and restraining them by hand; and firing a net-gun from a helicopter. I captured 6 lambs by hand on the ground, 4 lambs by hand from the helicopter, and 11 lambs from the helicopter with a shoulder-mounted and skid-mounted net-gun. No injuries occurred to lambs or capture personnel. The hand capture technique allowed me to capture very young lambs. I then monitored lambs for mortality, and examined carcass and site characteristics to determine cause. I found that the primary proximate cause of lamb mortality was cougar predation, followed by golden eagle predation. Coyotes and bobcats did not kill lambs. Although 1 lamb died from pneumonia, disease was not a critical factor affecting lamb recruitment. I measured habitat characteristics at sites where adults and lambs were killed by cougars and paired control sites, and derived habitat characteristics at predation sites, relocation sites representing used areas, and random sites representing available areas. Visibility was lower at predation than control sites, while slope, elevation, and ruggedness were lower at predation than relocation sites, and predation sites were closer to water and roads than random sites. I suggest selective cougar control of habitual sheep killers over the short term may be an appropriate management strategy to enhance the recovery of desert bighorn populations, while recognizing the importance of carnivore ...