[Illustration: FIG. 13: Photograph of microclimatic station at the Pinyon-Juniper-Muttongrass Site, at trapping station D5b of the grid south of Far View Ruins. Grass in the foreground is muttongrass, _Poa fendleriana_.] The instruments used in this study were unmodified Belfort hygrothermographs containing as sensing units a hair element for relative humidity and a Bourdon tube for air temperatures. The hair element, especially, does not register changes in humidity at precisely ground level; rather, it reflects changes in the layer of air from about ground level to about a foot above. Thus data from these instruments give only approximations of the conditions under which mice live while they are on the ground. Climatic conditions greatly influence trapping success. Larger numbers of mice generally were caught on nights when humidities were higher than average. Rain in part of the evening almost invariably resulted in more mice of each species being caught. This was probably due to increased metabolism, by the mice, to keep warm. Apparently the mice began foraging as soon as the rains subsided; mice were always dry when caught after a rain. Few mice were caught if rains continued throughout the night and into the daylight hours. TABLE 4--Monthly Averages of Daily Means for Maximum, Minimum, and Mean Air Temperatures and Relative Humidities at Four Sites in Mesa Verde National Park, Colorado. ===================+========================+======================== Site | Maximum Temps. | Maximum R. H. | J J A S O | J J A S O | | Far View Sagebrush | 89 91 86 77 74 | 68 84 82 88 71 Drainage | 86 91 85 78 78 | 87 94 93 96 84 Oak Brush | 86 88 82 76 81 | 57 78 80 80 66 Pinyon-Juniper-Poa | 75 80 74 66 64 | 59 83 82 88 58 | | | Minimum Temps. | Minimum R. H. | J J A S O | J J A S O | | Far View Sagebrush | 42 53 50 42 31 | 18 24 25 29 21 Drainage | 36 48 45 38 26 | 21 26 27 29 30 Oak Brush | 42 52 50 42 32 | 19 25 30 31 21 Pinyon-Juniper-Poa | 44 54 50 42 34 | 22 30 29 32 25 | | | Mean Temps. | Mean R. H. | J J A S O | J J A S O | | Far View Sagebrush | 66 72 68 60 52 | 43 54 54 48 46 Drainage | 61 70 65 58 52 | 54 60 60 62 52 Oak Brush | 64 70 66 59 56 | 38 51 55 56 44