Featured Article Survival and Cause-Specific Mortality of Desert Bighorn Sheep Lambs JAMES W. CAIN, III , 1 U.S. Geological Survey, New Mexico Cooperative Fish and Wildlife Research Unit, New Mexico State University, Department of Fish, Wildlife and Conservation Ecology, P.O. Box 30003, MSC 4901, Las Cruces, NM 88033, USA REBEKAH C. KARSCH, 2 New Mexico State University, Department of Fish, Wildlife and Conservation Ecology, P.O. Box 30003, MSC 4901, Las Cruces, NM 88003, USA ELISE J. GOLDSTEIN, New Mexico Department of Game and Fish, 1 Wildlife Way, Santa Fe, NM 87507, USA ERIC M. ROMINGER, New Mexico Department of Game and Fish, 1 Wildlife Way, Santa Fe, NM 87507, USA WILLIAM R. GOULD, New Mexico State University, Applied Statistics Program, P.O. Box 30001, Las Cruces, NM 88003, USA ABSTRACT Juvenile recruitment in desert bighorn sheep (Ovis canadensis mexicana) is highly variable, yet the mechanisms influencing neonate survival are not well understood. Because few studies have equipped desert bighorn sheep lambs with telemetry collars, definitive data on cause-specific mortality, and lamb survival estimates are lacking. Our objectives were to estimate lamb survival rates and determine cause- specific mortality for desert bighorn sheep lambs during a period of mountain lion (Puma concolor) and coyote (Canis latrans) removal in southwestern New Mexico, USA. We captured pregnant adult females each fall and fitted them with a telemetry collar and a vaginal implant transmitter to aid with neonate captures. We captured and radio-collared 12 desert bighorn sheep lambs in 2012 and 14 in 2013 within 48 hours of parturition in the Peloncillo Mountains, New Mexico. We estimated lamb survival to 6 months of age. Across both years there were 14 mortalities, 12 of which were due to predation. Mountain lions killed 5 lambs (2 in 2012 and 3 in 2013), coyotes killed 4 lambs (all in 2013), a gray fox (Urocyon cinereoargenteus) killed 1 lamb in 2012, and 2 lambs were killed by unknown predators in 2013. Staged-based survival estimates indicated the highest mortality rates occurred in the first week post birth; 5 of 14 lamb mortalities occurred before 7 days of age. Lamb survival to 6 months was substantially lower in 2013 (0.20  0.11 [SE]) than in 2012 (0.71  0.14) with the differences in survival attributed to increased coyote predation in 2013. We did not detect differences in body mass at birth between years or differences in body mass, chest girth, or neck circumference at birth between lambs that were killed by predators and those that survived. Coyotes, mountain lions, and the gray fox killed lambs <8 weeks of age, but only mountain lions killed lambs >8 weeks old. Predator removals focused around the parturition period of desert bighorn sheep may be more likely to influence lamb survival rates than removals outside of the lambing season. Ó 2018 The Wildlife Society. KEY WORDS coyote predation, desert bighorn sheep, juvenile recruitment, lamb survival, mortality, mountain lion predation, Ovis canadensis mexicana, vaginal-implant transmitter. Neonate survival is the primary demographic rate affecting population growth in ungulates when adult survival is high and relatively constant (Gaillard et al. 1998, 2000; Raithel et al. 2007). Juvenile survival rates have high interannual variability, particularly in ungulates inhabiting arid and semi-arid environments (Leopold and Krausman 1991, Lawrence et al. 2004, Simpson et al. 2007, McKinney et al. 2008). High adult survival and variable juvenile survival often characterize desert bighorn sheep (Ovis canadensis mexicana) populations (Rubin et al. 2000, Wehausen 2005, McKinney et al. 2006a). Despite high pregnancy and birth rates (e.g., >90% of breeding age females produce one lamb each year; Etchberger and Krausman, 1999, Overstreet 2014), juvenile recruitment in desert bighorn is extremely variable and often low (e.g., <0.20; Bradley and Baker 1967, Hansen 1967, DeForge and Scott 1982, Douglas and Leslie 1986, Douglas 2001). Previous work has implicated a strong link between precipitation, particularly fall and winter rainfall, and juvenile recruitment in desert bighorn sheep populations (Douglas and Leslie 1986, Wehausen et al. 1987, Douglas 2001, McKinney et al. 2001). Few studies, however, have equipped desert bighorn lambs with telemetry collars and data on cause-specific mortality and estimates of lamb survival are lacking for most populations (Krausman and Shackleton 2000, Parsons 2007). Received: 23 May 2018; Accepted: 26 September 2018 1 E-mail: jwcain@nmsu.edu 2 Present Address: U.S. Forest Service, Coronado National Forest, 300 West Congress Street, Tucson, AZ 85701, USA. The Journal of Wildlife Management 83(2):251–259; 2019; DOI: 10.1002/jwmg.21597 Cain et al.  Desert Bighorn Sheep Lamb Survival 251