This study measured the population dynamics of coyotes in the grasslands and creosote shrublands of McKenzie Flats, Sevilleta National Wildlife Refuge. The study was begun in January, 1992, and continued quarterly each year. Coyotes were sampled via scat counts along the roads of McKenzie Flats during winter, spring, summer, and fall of each year. The entire road transect was 21.5 miles in length. Scat counts over a week period (number of scats/mile/day) in each season along the roads were used to calculate the densities of coyotes (number of coyotes per square kilometer). Results from 1992 to 2002 indicated that autumn was the peak density period of the year, with generally steady declines through the year until the following autumn. Coyote populations appeared to fluctuate seasonally, but remained relatively stable at 0.27 +/- 0.03 (SE) coyotes per km2 during summer periods (this likely represents the "breeding pair" density, during which coyote pairs have set up territories and are raising young, but the pups have not as yet joined the parents in foraging activities).
The purpose of the study was to assess the dynamics of coyote populations in the grasslands and creosote shrublands of the Sevilleta NWR. Coyotes are important predators and omnivores in these habitats, feeding on a wide variety of vertebrates, arthropods, and plants. Populations of prey species may be controlled to some extent by coyote predation, in which case coyotes may have significant influences on the biodiversity and species composition of the desert grassland ecosystem.
Density values were computed as numbers of individuals per square kilometer. According to F. Knowlton (see reference below), the relationship between absolute densities of coyotes (x-value, independent variable) and the number of scats per night per mile x 100 (y-value, dependent variable) is:
Y = 2.66 + 11.42X, r2 = 0.97, n = 8.
Transforming this equation for computing densities of coyotes from numbers of scats for each "leg" of the survey, and converting these values to numbers of coyotes per square kilometer, the coyote density equations for each survey "leg" are as follows:
D = Density of coyotes/km2
N = Total Number of Scats Collected/Leg after a 7-day period
Leg A (5.7 miles): D = [0.2195(N) - 0.2329]/2.59
Leg B (4.1 miles): D = [0.3052(N) - 0.2329]/2.59
Leg C (6.1 miles): D = [0.2052(N) - 0.2329]/2.59
Leg D (5.6 miles): D = [0.2235(N) - 0.2329]/2.59
The number of scats deposited by coyotes per mile of roadway per day in a typical western basin-and-range landscape has been shown to be correlated with the absolute density of coyotes. Therefore, the objective was to measure the deposition rate of coyote scats on the roads of McKenzie Flats.
The process involved two samplings along the roads. The first sampling involved the "clearing" of scats from the 21.5 mile survey route, so as to initialize the roadway with zero scats. On the assigned day, the technician would drive an ATV slowly (less than 5 miles per hour) along the route. When a coyote scat was observed, the technician would stop and pick up the scat, placing it into a zip-lock plastic bag that was labeled with the date and the "leg" letter. Each "leg" was bagged separately. The odometer reading of the scat location was recorded on the data sheet. If more than one scat was observed at the same place, the number of scats was recorded as well. For health and safety, the technician wore gloves during this process, or used tongs or a small trowel to pick up the scats and place them into the bag. When using the ATV, the technician wore a safety helmet.
During the early sampling periods (1992 to 1993), prior to the acquisition of the ATV in 1994, scats were collected by two technicians in a pick-up truck. One technician would drive, and the other would ride on the engine hood above the bumper, and scan the road as the truck was driven slowly along the road. When a scat was observed, the driver would stop the truck while the rider would collect the scat. The same data were recorded as described above.
One week following the "road clearing" survey, a second collection took place. The scats were sampled in the same fashion as before, but each scat was placed individually in a labelled small zip-lock plastic bag. Again, odometer readings were taken at the point of collection. Multiple scats from the same location were placed in separate plastic bags.The scats were then returned to the field station, and placed in freezers for preservation pending analysis of dietary items.
Missing Data Values
Two data values were missing from the densities estimates due to road construction at the normal time of scat sampling. These were in the summer of 1993 (August) and the winter of 1994 (January). For completion of the coyote density graph, these two values were estimated from the trends observed in the other years (1992-1997). For the value in summer, 1993, the mean percentage decrease observed between the spring and summer values in other years was calculated, and that percentage (38.76%) was multiplied by the spring, 1993, density value of 0.79 coyotes/km2. Similarly, the winter, 1994, density value was estimated by calculating the percentage difference between the other years' winter and spring density values (40.75%) and multiplying the spring, 1994, value of 0.42 coyotes/km2 by 1.4075. Estimates of the standard errors were calculated in the same fashion, using the mean percentage standard error and multiplying it by the estimated means. The two seasonal values calculated using this method are noted in the data set below.
The scats were sampled along 21.5 miles of roadway that was broken up into four "legs" of varying lengths.
Leg A: Black Butte southward to Five Points (5.7 miles)
Leg B: Five Points eastward to the turnoff before Palo Duro Canyon (4.1 miles)
Leg C: Palo Duro turnoff northward to the old McKenzie Headquarters site (6.1 miles)
Leg D: McKenzie Headquarters site northwestward to Black Butte (5.6 miles).
9-15-97; doc file created by Robert R. Parmenter.9-19-97; archived by Gregg MacKeigan as coyote_density_92-97.dbf.11-10-97; density data for October, 1997, entered and checked by R. Parmenter.12-26-00; density data for 2000 entered and checked by R. Parmenter.7-3-02; density data for 2001 and February and May entered and checked by R. Parmenter.8-2-02; density data for July, 2002, entered and checked by R. Parmenter.12-30-05; density data for 2002-2004 entered and checked, and final edits to the metadata file were made by R. Parmenter.8-2-02; density data for July, 2002, entered and checked by R. Parmenter.12-30-05; density data for 2002-2004 entered and checked, and final edits to the metadata file were made by R. Parmenter.
The data was visually checked for errors and missing values were commented on.
Additional Information on the Data Collection Period
The samples (scats) were collected in winter, spring, summer, and fall, of each year. Scats were collected from the road once at the beginning of a collection period, and once at the end (usually, one week later) during each of these four seasons per year. Months of collection varied in some years, but generally the sampling was conducted in January, April, July, and October. The study began in January, 1992 and ended in July 1994. Sampled one week per season, four seasons per year.
Additional Study Area Information
Study Area Name: McKenzie Flats
Study Area Location: The northeast section of the Sevilleta, stretching from Black Butte south to the canyon and east to the Los Pinos. McKenzie Flats, between black Butte, 5 Points, Palo Duro Canyon, and the old McKenzie headquarters ranch building site.
Study Area Description: The study area consisted of the roads that cross McKenzie Flats. The length of the road used in the study was 21.5 miles. The individual sites of measurements were the locations of each individual scat during each sample period.
Elevation: 1615 m
Vegetation: The terrain was generally mixed-species desert grassland, dominated by black grama (Bouteloua eriopoda), blue grama grass (B. gracilis), sand muhly (Muhlenbergia arenicola), various drop seeds and sacatons (Sporobolus spp.), purple three-awn (Aristida purpurea), and burrow grass (Scleropogon brevifolia). Shrubs were common in Five Points area; these were creosote bush (Larrea tridentata) and snakeweed (Gutierrezia sarothrae).
Soils: Turney Series: fine-loamy, mixed, thermic Typic Calciorthids. Berino Series: fine-loamy, mixed, thermic Typic Haplargids.
Hydrology: Surface water only during rain events, no arroyos. Run on plain for Los Pinos Mountains.
Landform: McKenzie Flats is a broad, nearly flat grassland plain between the Los Pinos Mountains and the breaks on the east side of the Rio Grande.
Geology: Deep (20,000 ft) alluvial and eolian deposits.
Climate: Long-term mean annual precipitation is 243 mm, about 60% of which occurs during the summer. Long-term mean monthly temperatures for January and July are 1.5°C and 25.1°C, respectively.
Site history: McKenzie Flats encompasses an area of approximately 50 square miles. McKenzie Flats was one of the primary livestock grazing areas of the Sevilleta NWR. The ranch headquarters buildings and corrals were located at the junction of Legs C and D of this coyote survey. Cattle have been excluded from the site since 1974-76.
Knowlton, Frederick F. 1984. Feasibility of Assessing Coyote Abundance on Small Areas. Unpublished USDA Report, 14 pp.