Seasonal Activity Patterns of Rodents in a Sagebrush Community

Abstract

Twelve species of nocturnal rodents were studied on a 2.7-hectare plot of sagebrush desert in west-central Nevada. Six species, Dipodomys merriami, D. ordii, D. panamintinus, D. microps, Onychomys torridus, and Peromyscus maniculatus, were active throughout the year. Four species, Perognathus longimembris, P. formosus, Microdipodops megacephalus, and Reithrodontomys megalotis, hibernated and were active only in spring, summer, and autumn. Onychomys leucogaster and Neotoma lepida were trapped intermittently throughout the year but were not permanent residents on the area. Differences in time of daily activity were found between potential competitors demonstrating a degree of temporal isolation. Time after sunset and amount of moonlight were the two most important factors correlated to rodent activity. Ambient temperature, wind, cloud cover, precipitation, and water vapor pressure had little effect on activity except when extreme conditions prevailed.The desert supports a wide variety of rodents and provides a natural laboratory to study the effect of rigorous environmental conditions on small mammal species. Numerous studies have been made on rodents of the low desert of the southwestern United States, but the sagebrush community of the Great Basin has been neglected. Hall (1946) provided the most complete information on species of the Upper Sonoran Life-zone. Since then mostly fragmentary information on the biology of these rodents has become available. However, Kenagy (1973) presented excellent comparative information for several desert species.A continuing problem in mammalian ecology concerns the methods by which sympatric species coexist. In the sagebrush desert of west-central Nevada at least 12 species of nocturnal, surface-active rodents coexist sympatrically. With such a large number of species, it was apparent that the sage desert provided a unique opportunity to study various mechanisms of coexistence.The purpose of the present study was to examine daily and seasonal activity patterns of nocturnal rodents. The major approach was measurement of frequency of captures throughout the night. Various environmental parameters were monitored concurrently as possible correlates to activity. The focal point of the study was to describe the trends in activity of individual species and to relate the patterns exhibited by potentially competing species. Likewise, environmental factors were examined to establish a predictive base for species behavior in relation to general environmental conditions. MATERIALS AND METHODSThe study area was located at the northern end of Warm Springs Valley, about 40 kilometers (km) north of Sparks, Highway 33, Washoe Co., Nevada (1363 meters, m, elevation). The selected site was approximately 200 m east of the highway. A 12 by 12-station grid, 2.7 hectares, was staked out at 15 m intervals. Vegetation primarily consisted of 809

Temporal Changes in a Chihuahuan Desert Rodent Community

“…Correlations of rodent densities with annual plant densities, annual population cycles in some species, and the tendency for many species to show positively correlated inter-annual fluctuations all suggest that population dynamics respond to environmental variation (see also Kenagy 1973, O'Farrell 1974, Kenagy and Bartholomew 1985. O n the other hand, the fact that none of these patterns were consistent across all species has two implications.…”

Biological Resources Survey of Mountain Springs Canyon on the Naval Weapons Center.

“…Aside from the fact that Feral Burro impact in the area was significant, the two factors that were present which could have affected trappability was the presence of a full moon and inclement weather. Moonlight is known to have a restrictive influence on activity and movements for desert rodents 4 (Lockard and Owings, 1974;O'Farrell, 1974;Kaufman and Kaufman, 1982). The inclement weather experienced during the present study consisted of unseasonable cold, high winds, and intermittent rain, which was part of an extended unusual and unseasonable spring season i,A the Mojave Desert Region.…”

Ecology and conservation of the northern hopping-mouse and sympatric vertebrates of Groote Eylandt

“…Because of this, we expected sustained activity throughout the night for the rodents, including peaks of activity soon after dark to replenish energy lost during the day (O'Farrell 1974;Vieira and Baumgarten 1995). Although this was evident for all species in some of our results, the effect was not consistent for all seasons and habitats.…”

“…Nightly illumination would be heavily influenced by the seasons due to cloud cover and is likely more important than lunar cycle in its effect on small mammal activity (O'Farrell 1974). Future studies on the effect of moonlight and other types of illumination on these species would be useful.…”

“…Seasonal rainfall, as a driver of fluctuating food resource abundance, probably exerts a strong influence on mammalian activity patterns at the study site. Based on these considerations, we hypothesize that the availability of food is a dominant influence on small mammal activity, and use this hypothesis to make the following predictions: 1) Nocturnal species will become active soon after sunset to replenish energy lost during the day (O'Farrell 1974;Vieira and Baumgarten 1995);…”