consisted of two lines of traps, each 1,000 feet long having 20 trapping stations that were 50 feet apart. The lines were either parallel at a distance of 400 feet from each other, or were joined to form a line 2,000 feet long. Three snap traps were placed within a five-foot radius of each station, and were set for three consecutive nights. More than a dozen areas were selected for extensive trapping (Fig. 1). Some of these were retrapped in consecutive years in order to measure changes in populations.

One circular trapline of 159.5 feet radius was established in November 1961, and was tended for 30 consecutive days to observe the effect of removing the more dominant species (Calhoun, 1959).

Other mouse traps and rat traps were set in suitable places on talus slopes, rocky cliffs, and in cliff dwellings. Most of these traps were operated for three consecutive nights.

In order to test hypotheses concerning habitat preferences of each of the species of Peromyscus, several previously untrapped areas that appeared to be ideal habitat for one species, but not for the other, were selected for sampling. In the summers of 1963 and 1964 snap traps were set along an arbitrary line through each of these areas. Traps were placed in pairs; each pair was 20 feet from the adjacent pairs.

A mixture of equal parts of peanut butter, bacon grease, raisins, roman meal and rolled oats was used as bait. Rolled oats or coarsely ground scratch feed was used in areas where insects removed the mixture from the traps.

Rodents trapped by me were variously prepared as study skins with skulls, as flat skins with skulls, as skeletons, as skulls only, or as alcoholics. Representative specimens were deposited in The University of Kansas Museum of Natural History. In the course of my study, traps were set in the following areas:

In July 1959 a fire destroyed more than 2,000 acres of pinyon-juniper forest (Pinus edulis and Juniperus osteosperma) in the eastern part of the park. The burned area extends from Morfield Canyon to Waters Canyon, encompassing several canyons, Whites Mesa, and a ridge between Morfield Canyon and Waters Canyon that is known locally as Morfield Ridge (Fig. 1). Beginning on September 4, 1961, three pairs of traplines were run on this ridge at elevations of 7,300 to 7,600 feet.

Vegetation in the trapping area consisted of dense growths of grasses and herbaceous plants, which had covered the ground with seeds. In this and in the following accounts, the generic and specific names of plants are those used by Welsh and Erdman (1964). The following plants were identified from the trapping area on Morfield Ridge:

Only Peromyscus maniculatus, Perognathus apache and Reithrodontomys megalotis were taken in this area (Table 1). Many birds inhabit this area, including hawks, ravens, towhees, jays, juncos, woodpeckers, doves, sparrows and titmice. Rabbits, badgers and mule deer also live in the area. Only two reptiles, a horned lizard and a collared lizard, were seen.

Two parallel trap lines were established on October 4, 1961, in the area immediately south of Far View Ruins (Fig. 1). In altitude, latitude and geographical configuration the area is similar to that trapped in the Morfield burn, but the Chapin Mesa site had not been burned.

Canopy vegetation is pinyon-juniper forest. A dense understory was made up of Amelanchier utahensis (serviceberry), Cercocarpos montanus (mountain mahogany), Purshia tridentata (bitterbrush), and Quercus gambelii (Gambel oak). The ground cover consisted of small clumps of Poa fendleriana (muttongrass), and Koeleria cristata (Junegrass), intermingled with growths of one or more of the following:

Seeds of Cercocarpos montanus covered the ground under the bushes in much of the trapping area, and large numbers of juniper berries were on the ground beneath the trees. Individuals of P. truei and P. maniculatus were caught in this area (Table 1).

Several deer, rabbits, one coyote, and numerous birds were seen in the area. No reptiles were noticed, but they were not searched for. A mountain lion was seen in this general area two weeks after trapping was completed.

Three pairs of traplines were run west of Far View Ruins in an area comparable in vegetation, altitude, general topography, and configuration to the area previously described. The elevations concerned are typical of the middle parts of mesas throughout the park. This area differs from the trapping area south of Far View Ruins and the one on Morfield Ridge in being wider and on the western side of the mesa.

The woody understory was sparse in most places, and where present was composed of Cercocarpos montanus, Purshia tridentata, Fendlera rupicola (fendlerbush), Amelanchier utahensis, Quercus gambelii, and Artemisia tridentata (sagebrush). The herbaceous ground cover was dominated by Solidago petradoria (rock goldenrod), and grasses—including Poa fendleriana, Oryzopsis hymenoides, and Sitanion hystrix. Other herbaceous species were as follows: