Academic journal article The American Midland Naturalist

Adult Pronghorn (Antilocapra Americana) Survival and Cause-Specific Mortality in Custer State Park, S.D

Academic journal article The American Midland Naturalist

Adult Pronghorn (Antilocapra Americana) Survival and Cause-Specific Mortality in Custer State Park, S.D

Article excerpt

ABSTRACT.-

Although understanding natural mortality rates of ungulate populations is essential for effective management, published data on adult survival from unharvested pronghorn (Antilocapra americana) populations in the Northern Great Plains is limited. We estimated seasonal adult survival rates and cause-specific mortality of an unharvested pronghorn population in Custer State Park, S.D. We assessed the relative importance of sex, age, year, and season in explaining pronghorn survival rates using an information-theoretic approach. We captured and radio-collared 26 male and 24 female adult pronghorn from fall 2005 through spring 2008. We observed higher predation rates and lower survival of adult pronghorn in CSP compared to other populations in the region, but similar to the pronghorn population in Yellowstone National Park. We documented 23 deaths (10 females, 13 males) of the 50 radio-collared pronghorn from Nov. 2005-Nov. 2008. Predation by mountain lions (Puma concolor) and coyotes (Canis latrans) accounted for 69.5% of all mortalities. The season model received the greatest support although there also was strong support for the season X sex model. Seasonal survival for males and females was >0.90 for the winter-grouping and breeding seasons but fell to 0.791 (95% CI 0.644-0.887) and 0.837 (95% CI 0.706-0.916) for females and males, respectively, during the small group - parturition season. A dense predator population, as well as a higher vulnerability to predadon when pronghorn are solitary or in small groups, may explain the lower survival during these time periods. If population estimates fall below management goals, management actions aimed at reducing predator cover may be beneficial to adult pronghorn. Managers of pronghorn populations near forested and rugged areas and that are sympatric with dense predator populations should consider adult survival may be lower than observed in Great Plains populations.

INTRODUCTION

Accurate estimates of sex- and age- specific vital rates are essential to understand the mechanisms driving the population dynamics of ungulates and to model the effects of management actions on population growth. The majority of literature concerning pronghorn (Antilocapra americana) vital rates focuses on neonatal survival (Canon, 1993; Avsharian and Byers, 2001; Gregg et al., 2001; Sievers, 2004; Berger and Conner, 2008) since that parameter is often most variable within ungulate populations (Gaillard et ai, 1998; Avsharian and Byers, 2001). However, survival of adult females is widely recognized as the most influential vital rate affecting ungulate population growth (Heppell et al., 2000; Brown et ai, 2006), and when adult female survival is variable and low it may lead to population extinction regardless of neonatal survival (Gaillard et al., 2000). Natural mortality of adult males is also an important yet under-reported component of ungulate population dynamics. Low male survival can cause delayed breeding of females and thus delayed, less synchronous calvingleading to higher neonatal predation rates and lowered population growth (Mysterud et al., 2002).There is evidence that adult male survival is typically lower and more variable than adult female survival for a variety of ungulate species (Loison et al, 1999; Toigo and Galliard, 2003). Further, adult males are highly-valued by the general public for viewing and hunting (Mysterud, 2011) and data on natural mortality rates of males is important to avoid overharvest (Bender et ai, 2004).

It is also necessary to identify the factors affecting survival so management actions can target underlying causes of mortality. Sources of mortality for adult pronghorn include predation (Cannon, 1995; Sievers, 2004; Jacques and Jenks, 2008; Barnowe-Meyer et ai, 2009), hunter, harvest (Grogan and Lindzey, 2007; Jacques et ai, 2007; Kolar et ai, 2012), malnutrition, weather-related starvation (West, 1970; Barrett, 1982; Brown et ai, 2006), disease (Wobeser et ai, 1975; Thorne et ai, 1988), fence entanglement (Harrington and Conover, 2006; Kolar et ai, 2012), vehicle collisions (Gavin and Komers, 2006;Jacques et ai, 2007), and parturitional complications (Jacques et ai, 2007), among others. …

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