Population Characteristics of Coyotes (Canis Latrans) in the Nothern Chihuahuan Desert of New Mexico

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LAMAR A. WINDBERG,1 STEVEN M. EBBERT2 AND BRIAN T. KELLY3

ABSTRACT.-We estimated demographic variables for a coyote (Canis latrans) population in the northern Chihuahuan Desert in spring 1991. Indices of coyote abundance indicated that the population was in a decline phase during 1991. Of 41 coyotes radio-collared on the Jornada Experimental Range near Las Cruces, New Mexico, only 7% were juveniles and a relatively high percentage (40%) were transient (nonterritorial) animals. Size of the core areas of 10 territorial ranges occupied by 13 coyotes averaged 5.6 km2. None of 11 radiocollared females produced viable fetuses in 1991. We examined data from earlier studies to assess factors affecting population dynamics in the region. Autumn scent-station indices of coyote abundance were positively correlated with annual rainfall (July to June) during 19721981. Low recruitment in the population during 1991 may have resulted from the combined effect of relatively low rainfall and high coyote abundance in the preceding 2-3 yr.

INTRODUCTION

Coyote (Canis latrans) population dynamics are influenced by interactions between their social organization and food availability (Knowlton and Stoddart, 1983; Windberg, 1995) and by the degree of human exploitation (Knowlton, 1972; Davison, 1980). Demography (Todd and Keith, 1983; Gese et al., 1989; Windberg, 1995) and social structure (Camenzind, 1978; Andelt, 1985) vary locally within the coyote's diverse geographic range.

The Chihuahuan Desert (355,000 km ^sub 2^) encompasses most of N-central Mexico and extends northward into southern New Mexico and western Texas (Schmidt, 1979). Temporal fluctuations in density and diversity of rodent populations in the Chihuahuan Desert are related to variations in forage (Whitford, 1976; Hallett, 1982; Brown and Heske, 1990), which are influenced by annual rainfall. Although rainfall and prey abundance potentially affect dynamics of coyote populations, demographic analyses for coyotes in this region are limited.

We collected population data for coyotes in conjunction with a study of predation on livestock (Windberg et al., 1997). Our objectives were to estimate age and sex distributions, natality, and social composition of the population during spring 1991, examine long-term coyote population trends in the region, and investigate factors influencing dynamics of this population.

METHODS

The 75 km ^sup 2^ study area was located on the northern portion of the U.S. Department of Agriculture (U.S. Dep. Agric.) Jornada Experimental Range (JER), 40 km N of Las Cruces, Dona Ana County, New Mexico. The 783-km ^sup 2^ JER is characterized by basin topography representative of the northern Chihuahuan Desert (Hennessy et al., 1983). The elevation of the study area ranged from 1320 to 1390 m. The climate is arid, with annual precipitation concentrated in late summer (Hennessy et al., 1983). Invading mesquite (Prosopis glandulosa) occurs on most of the plains, and large dunefields have formed on the predominantly sandy soils (Buffington and Herbel, 1965). Permanent water on the study area was limited to one earthen impoundment and three livestock water troughs during spring 1991. The primary prey of coyotes on the JER during the study appeared to be lagomorphs and rodents based on our cursory examination of coyote feces on the area.

We trapped (3431 trap days) and radio-collared coyotes from 19 February to 21 March 1991 (plus one coyote in November 1990). We used foothold traps with tranquilizer tabs containing 600 mg of propiopromazine hydrochloride to reduce injury and trauma to captured coyotes (Balser, 1965). We measured body mass and length (tip of nose to base of tail) of each coyote, and extracted a vestigial premolar tooth for age analysis. We recovered radio-collared coyotes by aerial shooting during 29-31 May 1991. We removed canine teeth from all coyotes recovered, and preserved and examined ovaries and uteri of females as described by Windberg (1995). …