Visual Observation of Bobcat Predation on an Adult Female Pronghorn in Northwestern South Dakota

Article excerpt

ABSTRACT.-

Published reports of survival and cause-specific mortality for pronghorn (Antilocapra americana) indicate that mortality differs regionally and seasonally with sex, age and density of pronghorn. Cold winters with deep crusted snow is a primary source of mortality on adult pronghorn, however, predation also can be an important source of adult mortality. We report a visual observation of bobcat (Felis rufus) predation on an adult female pronghorn in northwestern South Dakota.

INTRODUCTION

Cause-specific mortality is well documented in pronghorn (Antilocapra americana) populations throughout western North America (reviewed by O'Gara and Yoakum, 2004). Numerous radio telemetry studies have demonstrated that mortality differs regionally and seasonally with sex, age, and density of pronghorn (Martinka, 1967; Fairbanks, 1993; Gregg et al., 2001; Jacques et al, 2007). A review by Yoakum and O'Gara (2000) identified cold winters with deep crusted snow as a primary source of mortality on adult pronghorn in northern regions and Brown et al. (2006) concluded that impacts of drought on pronghorn productivity may be more important than severe winters in the southwestern United States.

Predation also has been documented as a primary source of mortality on adult pronghorn (Yoakum, 1978). Coyotes (Canis fotrans; Yoakum, 1978; O'Gara and Yoakum, 2004), golden eagles (AquiUi chrysaetos; O'Gara, 1978) and domestic dogs (C. familiaris; Mitchell, 1980) have been identified as significant predators of pronghorn. Feline predators also have been identified as main predators of pronghorn. For instance, mountain lions (Felts concolor) have been documented as a major predator on adult pronghorn in southern regions (Engstrom and Maxwell, 1988; Canon and Bryant, 1992; Ockenfels, 1994a, b) while bobcat (F. rufus) predation on pronghorn fawns has been identified as a significant cause of mortality (Beale and Smith, 1973). Similarly, Nelson (1925) and Einarsen (1948) documented bobcat predation on adult pronghorn, however, these occurrences were confirmed following evaluation of carcasses and kill sites rather than direct visual observations of kill events. Dolbeer et al (1994) noted that predation is rarely observed and that accurate assessment of losses to specific predators often required careful investigation of carcasses and kill sites. O'Gara and Yoakum (2004) stated that although predators that fed on or killed an animal could usually be determined, overlaps and exceptions also occurred in feeding and killing behavior of various predators. Previous information on bobcat predation has been known and documented for nearly a century, however, direct visual observations of bobcat predation on adult pronghorn have not previously been recorded in the scientific literature.

RESULTS AND DISCUSSION

On 6 Apr. 2002 we captured and radiocollared an unbred adult female pronghorn (P1704) in Harding County, South Dakota, as part of a long-term research project that evaluated survival and seasonal movements of pronghorns in western South Dakota (Jacques, 2007). Using standard ground telemetry techniques, we visually located P1704 at approximately 1443 h on 22 Oct. 2002. At 1444 h, we visually observed a bobcat stalking Pl 704; the stalk continued until 1449 h, at which time the bobcat had successfully stalked to within 10 m of P1704. At 1450 h, the bobcat initiated an attack, at which time it captured Pl 704 and initiated a series of bites to the back of the neck while gripping the front shoulders with its claws; the bobcat repositioned itself and subsequently secured a fatal throat hold. The attack ended with the death of P1704 at approximately 1453 h. We observed the bobcat consume muscle tissue from the right hindquarter until 1458 h before we interrupted the feeding activity and initiated our investigation of the kill site. Presence of snow cover enabled a search of the kill site and surrounding area (i. …