Comparative Ecology of Pinyon Mice and Deer Mice in Mesa Verde National Park Part 2

Bobcat Canyon, a large secondary canyon on the eastern side of Wetherill Mesa, is a major drainage for much of the mesa at its widest part. The mesa top drains southeast into a pour-off at the head of Bobcat Canyon.

A stand of big sagebrush, _Artemisia tridentata_, grows in the sandy soil of the drainage, and extends northwest for several hundred yards from the pour-off. The sagebrush invades the pinyon-juniper forest at the periphery of the area.

Two traplines were set in the drainage, with trapping stations at intervals of 25 feet. The lines traversed elevations of 7,000 to 7,100 feet, and were run from June 26 to 29, 1962.

Gra.s.ses are the most abundant plants in the ground cover. _Artemisia dracunculus_ is common in the drainage, and _A. nova_ grows around the periphery of the drainage. Other species occurring in this stand include:

_Aster bigelovii_ _Tetradymia canescens_ _Tragopogon pratensis_ _Bromus tectorum_ _Poa fendleriana_ _Sitanion hystrix_ _Stipa comata_ _Lupinus argenteus_ _Calochortus gunnisonii_ _Sphaeralcea coccinea_ _Phlox hoodii_ _Eriogonum umbellatum_ _Peraphyllum ramosissimum_ _Purshia tridentata_ _Penstemon linarioides_

No mice were caught in three nights of trapping (360 trap nights), and only one mammal, a _Spermophilus variegatus_, was seen.

_North of Long House, Wetherill Mesa_

Pinyon-juniper forest with a dominant ground cover of _Poa fendleriana_ was described by Erdman (1962) as one of the three distinct types of pinyon-juniper woodland on Wetherill Mesa. Such a woodland occurs adjacent to the Bobcat Canyon drainage, and is continuous across the Mesa from above Long House to the area near Step House. Plants in the ground cover include:

_Cryptantha bakeri_ _Opuntia rhodantha_ _Chrysothamnus depressus_ _Solidago petradoria_ _Koeleria cristata_ _Lupinus argenteus_ _Yucca baccata_ _Phlox hoodii_ _Eriogonum racemosum_ _Eriogonum umbellatum_ _Cordylanthus wrightii_ _Pedicularis centranthera_ _Penstemon linarioides_ _Penstemon strictus_

Two traplines were run from July 9 to 12, 1962, in the area south of the Bobcat Canyon drainage at an elevation of 7,100 feet. No mice were caught in three nights of trapping. Four additional lines were established on July 24, 1962, and were run for three nights, in the area north of the Bobcat Canyon drainage at elevations of 7,100 to 7,150 feet.

_P. maniculatus_ and _P. truei_ were caught here (Table 1). This vegetational a.s.sociation may have few rodents because there is a shortage of places where they can hide. Although _Poa fendleriana_ is abundant, the lack of shrubs leaves little protective cover for mammals.

_Mug House--Rock Springs_

A juniper-pinyon-mountain mahogany a.s.sociation extends from the area of Mug House to Rock Springs, on Wetherill Mesa. On that part of the ridge just above Mug House, the understory is predominantly _Cercocarpos monta.n.u.s_ (mountain mahogany), but northward toward Rock Springs the understory changes to _Fendlera rupicola_, _Amelanchier utahensis_, _Cercocarpos_, and _Purshia tridentata_. The ground cover is essentially the same as that in the pinyon-juniper-muttongra.s.s a.s.sociation described previously.

Four traplines were run from July 31 to August 2, 1962, and from August 13 to 15, 1963. These lines ran northwest-southeast, starting 1,000 feet southeast of, and ending 3,000 feet northwest of, Mug House. The lines traversed elevations of 7,225 to 7,325 feet. Individuals of _P.

maniculatus_ and _P. truei_ were caught here (Table 1).

Deer and rabbits inhabit the trapping area. Bobcats have been seen, by myself and by others, near Rock Springs. Lizards of the genera _Cnemidophorus_ and _Sceloporus_, as well as gopher snakes were seen in this area.

_Juniper--Pinyon--Bitterbrush_

Three pairs of traplines were run from August 7-9, 1962, in a juniper-pinyon-bitterbrush stand on the southern end of Wetherill Mesa, starting 200 yards southwest of Double House (Fig. 1).

The forest on the southern end of the mesas consists of widely-s.p.a.ced trees, which reflect the low amounts of precipitation at these lower elevations. Juniper trees are more numerous than pinyons, and both species are stunted in comparison to trees farther north on the mesa.

_Purshia tridentata_ (bitterbrush) is the understory codominant.

_Artemisia nova_ (black sagebrush) is present and gra.s.ses are the most abundant plants in the ground cover. Herbaceous species in the spa.r.s.e ground cover include the following:

_Opuntia polyacantha_ _Solidago petradoria_ _Lathyrus pauciflorus_ _Penstemon linarioides_ _Lupinus caudatus_ _Yucca baccata_ _Phlox hoodii_

Only _P. maniculatus_ was caught in this stand; all mice were caught in the first night of trapping.

Five areas were selected for trapping in the summers of 1963 or 1964, in order to test hypotheses concerning habitat preferences of each of the species of _Peromyscus_. Four of these areas appeared to be ideal habitat for one species, but not for the other. The fifth area was expected to produce both species of _Peromyscus_. Each of these areas is discussed below.

_One Mile Southeast of Park's Entrance_

A small stand of _Artemisia tridentata_, occurring one mile southeast of the entrance to the park, is bordered to the north and northeast by a gra.s.sy meadow, discussed in the following account. Kangaroo rats have been reported in this general area, and I wanted to determine whether _P. maniculatus_ and _Dipodomys_ occurred together there. Fifty trap nights in this sagebrush, on June 20, 1963, yielded only _P.

maniculatus_ (Table 1).

_Meadow, One-Quarter Mile Southeast of Park's Entrance_

A gra.s.sy meadow lies just to the east of the highway into the park, one-quarter of a mile southeast of the park's entrance. On July 30, 1963, one hundred traps were placed in two lines through the meadow, and were run for one night. Only individuals of _P. maniculatus_ were caught (Table 1).

_M-2 Weather Station, Chapin Mesa_

The M-2 weather station of the Wetherill Mesa Archeological Project was on the middle of Chapin Mesa at an elevation of 7,200 feet. This site was in an old C. C. C. area, about one mile north of the park's U. S.

Weather Bureau station. The vegetation surrounding the M-2 site was a pinyon-juniper-muttongra.s.s a.s.sociation. It was thought that both species of _Peromyscus_ would occur in this habitat.

On May 10, 1964, 25 traps were placed in this area and were run for one night. Only individuals of _P. truei_ were caught (Table 1).

_Gra.s.sy Meadow, Southern End Moccasin Mesa_

This large meadow is located eight miles south of the northern rim of Moccasin Mesa. The meadow lies in a broad, shallow depression that forms the head of a large drainage (Fig. 1). To the south of the meadow the drainage deepens, then reaches bedrock as it approaches the pour-off.

On August 23, 1964, one hundred traps were set in pairs in a line through the middle of the meadow; adjacent pairs were 20 feet from each other. Only individuals of _P. maniculatus_ were caught (Table 1).

Gra.s.ses are dominant in the ground cover, and _Sphaeralcea coccinea_ (globe mallow) is codominant. The abundance of globe mallow is due to the present and past disturbance of this meadow by a colony of pocket gophers. Trees are absent in the meadow. Species of plants include the following:

_Opuntia polyacantha_ _Chenopodium_ sp.

_Artemisia ludoviciana_ _Chrysothamnus nauseosus_ _Koeleria cristata_ _Poa pratensis_ _Lupinus ammophilus_ _Calochortus gunnisonii_ _Erigeron speciosus_ _Gutierrezia sarothrae_ _Tetradymia canescens_ _Tragopogon pratensis_ _Bromus tectorum_ _Sphaeralcea coccinea_ _Eriogonum racemosum_ _Polygonum sawatchense_ _Comandra umbellata_ _Penstemon strictus_

_Bedrock Outcroppings, Southern End Moccasin Mesa_

Two miles south of the preceding site, much of the mesa is a wide expanse of exposed bedrock, which extends approximately 100 feet inward from the edges of the mesa. Pinyon-juniper-mixed shrub woodland adjoins the bedrock.

On August 23, 1964, 25 traps were placed along the bedrock, near the edge of the forest. Only two mice, both _P. truei_, were caught. (Table 1).

HOME RANGE

In order to learn how extensively mice of different ages travel within their habitats, whether their home ranges overlap, and how many animals live within an area, it was necessary to determine home ranges for as many mice, of each species, as possible (Hayne, 1949; Mohr and Stumpf, 1966; Sanderson, 1966).

In 1961, the Colorado Department of Fish, Game and Parks established a permanent trapping grid in the area south of Far View Ruins (Fig. 1). The grid was constructed and used by Mr. Harold R. Shepherd, Senior Game Biologist, and his a.s.sistant, in the summers of 1961 and 1962, in a study concerning the effect of rodents on browse plants used by deer.

The Department of Fish, Game and Parks allowed me to use the grid during 1963 and 1964, and also permitted me to use its Sherman live traps.

The grid is divided into 16 units, each with 28 stations (Fig. 2). Traps at four stations (1a, 1b, 1c, 1d) are operated in each unit at the same time, with two traps being set at each station. The traps are moved each day in a counter-clockwise rotation to the next block of four stations (2a, 2b, 2c, 2d) within each unit. The stations are arranged so that on any given night, traps in adjacent units are separated by at least 200 feet. As a result, animals are less inclined to become addicted to traps, for even within one unit they must move at least 50 feet to be caught on consecutive nights.

[Ill.u.s.tration: FIG. 2: Diagram of trapping grid for small mammals, showing units of subdivision. Trapping stations were numbered in each unit as shown in unit A.]