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Seed caching by desert rodents in the family Heteromyidae is an important behavioral adaptation for animals living in environments with limited and unpredictable food resources. Heteromyids cache seeds throughout their home ranges, either concentrated in 1 location (larder hoard) or in multiple, small seed piles (scatter hoards). To minimize cache pilferage by other rodents, coexisting species may scatter hoard seeds in distinct microhabitats. We examined interspecific differences in caching and pilfering behaviors of 3 coexisting heteromyid rodents, Merriam's kangaroo rat (Dipodomys merriami), the pale kangaroo mouse (Microdipodops pallidus), and the little pocket mouse (Perognathus longimembris), to determine if caching microhabitat affects likelihood of pilferage. In outdoor enclosures we tracked cache placement and measured pilferage of artificial caches using radiolabeled Indian ricegrass (Achnatherum hymenoides) seeds. M. pallidus and P. longimembris placed seed caches mostly under shrubs, whereas D. merriami placed caches predominately in open microhabitat. However, D. merriami showed a significant preference for pilfering caches under shrubs, whereas P. longimembris did not show a significant preference for pilfering caches in either open or undershrub microhabitats. The 2 species pilfered similar numbers of caches. Coexisting heteroymid rodent species may contribute to spatial heterogeneity of available resources by caching in different microhabitats, thereby reducing but not eliminating cache pilferage by other species.

We used program CAPTURE to analyze 1,535 capture–recapture data sets from 33 species of small mammals for sources of variation in capture probabilities and to characterize species-specific responses to mark–recapture trapping. Program CAPTURE contains 8 models to account for all possible combinations of heterogeneity (h), behavioral response (b), and time (t) effects on capture probabilities. Model Mo (equal capture probabilities) was selected most often by CAPTURE as the most appropriate model for small sample sizes, reflecting the difficulty of detecting unequal probabilities of capture in small data sets. Heterogeneity in capture probabilities among individuals was evident in larger data sets for all species of small mammals examined. Strong behavioral responses were detected in several species. Sylvilagus, Tamias amoenus, Glaucomys sabrinus, Perognathus longimembris, and Microtus ochrogaster were trap shy, whereas Tamias striatus, Tamias townsendii, Spermophilus richardsonii, Perognathus parvus, Reithrodontomys megalotis, Peromyscus maniculatus, Peromyscus truei, Sigmodon hispidus, Microtus californicus, and Microtus pennsylvanicus were trap prone. Time effects were not apparent for most species except where they were accompanied with heterogeneity. Murid species had the highest estimated probabilities of capture, followed by heteromyids, sciurids, and leporids in decreasing order. Estimates of abundance from model Mh were significantly greater than those from models Mb, Mo, and Mt, which likely reflects the negative bias of these latter estimators.

The Perognathus longimembris species group currently consists of 3 species and approximately 23 subspecies. Members of this species group have been of considerable interest to biologists in both physiological and ecological studies, and several members are threatened with extinction. No one has yet attempted a phylogenetic study including several populations from each of these 3 species to test the monophyly of these taxa and to elucidate the relationships among the species and subspecies. Mitochondrial DNA sequences from the cytochrome-b gene were used to assess the genetic variation among these species and to make a 1st approximation of the number of species that should be recognized taxonomically in this species group. Results indicate that the Arizona pocket mouse, P. amplus, and the San Joaquin pocket mouse, P. inornatus, are monophyletic entities, and should remain as single polytypic species, whereas the little pocket mouse, P. longimembris, is paraphyletic in the maximum-likelihood and maximum-parsimony phylogenies, suggesting that it might best be split into 2 polytypic species.

The foraging behavior of a predator species is thought to be the cause of short-term apparent competition among those prey species that share the predator. Short-term apparent competition is the negative indirect effect that one prey species has on another prey species via its effects on predator foraging behavior. In theory, the density-dependent foraging behavior of granivorous rodents and their preference for certain seeds are capable of inducing short-term apparent competition among seed species. In this study, I examined the foraging behavior of two heteromyid rodent species (family Heteromyidae), Merriam’s kangaroo rats (Dipodomys merriami) and little pocket mice (Perognathus longimembris). In one experiment I tested the preferences of both rodent species for the seeds of eight plant species. Both rodent species exhibited distinct but variable preferences for some seeds and avoidance of others. However, the differences in preference appeared to have only an occasional effect on the strength of the short-term apparent competition detected in a field experiment. In another experiment, I found that captive individuals of both rodent species had approximately equal foraging effort (i.e., time spent foraging) in patches that contained a highly preferred seed type (Oryzopsis hymenoides) regardless of seed density and the presence of a less preferred seed type (Astragalus cicer) in the patches. The rodents also harvested a large proportion of O. hymenoides seeds regardless of initial seed density; this precluded a negative indirect effect of A. cicer on O. hymenoides. But there was a negative indirect effect of O. hymenoides on A. cicer caused by rodents having a lower foraging effort in patches that only contained A. cicer seeds than in patches that contained A. cicer and O. hymenoides seeds. The indirect interaction between O. hymenoides and A. cicer thus represented a case of short-term apparent competition that was non-reciprocal. Most importantly, it was caused by the foraging behavior of the rodents.

Storing food is an important adaptation of heteromyid rodents to desert environments of southwestern North America. These rodents store seeds in burrows (larder hoarding) and in small, widely scattered caches buried at shallow depths in soil (scatter hoarding). Laboratory trials were done with five species from one site and two species from two other sites to test the hypothesis that larger species would larder hoard relatively more seeds than smaller species. Subjects were tested in arenas consisting of a sand-filled box for scatter hoarding and a nest box for larder hoarding. Chisel-toothed and Merriam's kangaroo rats ( Dipodomys microps and D. merriami ) from one site larder hoarded more than sympatric dark kangaroo mice ( Microdipodops megacephalus ) and long-tailed and little pocket mice ( Chaetodipus formosus and Perognathus longimembris ). Chisel-toothed kangaroo rats larder hoarded more than Merriam's kangaroo rats and little pocket mice larder hoarded more than dark kangaroo mice. These results were consistent with reported information on the relative aggressive behaviors of the species. For subjects from the other two sites, Ord's kangaroo rats ( D. ordii ) larder hoarded more than the smaller Merriam's kangaroo rats. Pocket mice made larger scatter hoards than kangaroo rats and placed these scatter hoards closer to edges and corners of arenas than kangaroo rats. Differences among species in food-hoarding behavior should be considered in future studies of the community ecology of desert rodents.

The relationship of death and age in pocket mice ( Perognathus longimembris ) was determined in a cohort of 216 animals derived from breeding experiments with field trapped animals. A maximum life span of 8.3 years was found. The pattern of mortality as revealed by a comparison of its qx curve with other rodents seems to be distinctly different. There is a prolongation of moderate mortality at a time when mortality rates of other mammals are tending toward a logarithmic increase. The ramifications of torpor on longevity and ecological strategy are discussed.

Removal trapping was used to study lability in microhabitat use by three heteromyid rodents in three widely separated localities. Among all sites, captures from the first night of trapping showed a similar pattern of microhabitat use: Dipodomys merriami was associated with open, sandy microhabitats, whereas Perognathus formosus and Perognathus longimembris were trapped in shrubby areas with, respectively, low and high percentages of sand. Continued removal of individuals (rarefaction) initiated shifts in microhabitats used by Perognathus at the Fallon Site; both species began to frequent the open areas previously occupied by Dipodomys alone. No shifts were detected at the other two sites although trapping was continued at Indian Springs for a much longer period and many more individuals were removed. Site-specific responses to rarefaction suggest that the processes underlying patterns of microhabitat use by rodents may vary geographically. These results weaken the widespread notion that localized studies can be extrapolated to generalizations of community organization over a broad area even when the same species comprise local assemblages.

Home range sizes were estimated seasonally for Microdipodops megacephalus and Perognathus longimembris and biweekly for Dipodomys merriami, D. ordii, D. panamintinus, D. microps , and Peromyscus maniculatus. Mean estimates are also presented for Reithrodontomys megalotis and Onychomys torridus . Principal component analysis was used to calculate home range values because of its ability to deal with a wide variety of home range configurations. All species showed great variability in home range size throughout the year. Shape of home range was similarly variable, although most species tended towards elliptical movement configurations. The heteromyids showed consistency in annual composite home range areas (0.33–0.49 ha) regardless of body size. The generally smaller cricetine rodents exhibited much larger composite home range areas (0.95–1.42 ha). Emphasis is placed on the utility of point-in-time estimates of movements rather than obtaining a single home range value, which subordinates the dynamic nature of small mammal movements.

Long-term patterns of surface activity were monitored in 15 pocket mice, Perognathus longimembris , which constructed burrow systems in dirt-filled terrariums kept at 16°c and 31°c on 12-hour photoperiods. a rhythm, with an average period of about 10 months, was evident in the behavior of the mice at 16°c. During each cycle, these animals spent several months continuously underground even though food was always available on the surface. The transition between the underground and surface active phases of the cycle was usually gradual. However, the mice immediately resumed nightly foraging if the upper layers of the soil were heated each day during this transition time. They did not respond to this stimulus during the middle of the underground phase of the annual cycle. I suggest that in nature the vertical uniformity of soil temperatures in the spring may cue the synchronization of the circannual rhythm with the seasons. The absence of surface activity is apparently unrelated to torpor because mice at 31°c, where torpor does not occur, also spent several months continuously underground. However, the regular 10-month periodicity of the behavioral cycle was disrupted in this hot environment. Torpor was also monitored for up to 20 months in 25 mice at 8°c and 18°c under 9-hour and 15-hour photoperiods, but circannual rhythms of torpor were not evident under these experimental conditions.

Nocturnal, above-ground movement patterns of three desert heteromyid rodents, Dipodomys merriami, Perognathus formosus , and Perognathus longimembris , were studied in a Mohave desert-scrub habitat. Dipodomys merriami moved long distances between stops, remained stationary for long periods of time and collected a low diversity of seeds when compared to the Perognathus . In contrast, both Perognathus moved short distances between stops, spent little time stationary, and collected a wide range of seed types. These differences are consistent with the hypothesis that Dipodomys forage for rich seed clumps, whereas Perognathus forage for more dispersed seed resources. That Dipodomys and Perognathus show differences in the diversity of seeds collected is additional evidence that intergeneric modes of foraging may differ. Differential foraging behaviors leading to the exploitation of seed resources may be one of the mechanisms which facilitates the coexistence of desert rodents.

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 of 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. (auth)

Perognathus longimembris , under a variety of conditions, demonstrated essentially a 24-hr rhythm in oxygen consumption. The amplitude, correlation with light cycle, and duration of periods of high and low metabolism varied. In September, mice provided with food and held at 22–24° C had a rhythm closely synchronized with a 12-hr light cycle (high in dark); mice were hypometabolic 12.5% of the days. In May, mice were more often out of synchrony and were hypometabolic 32.5% of the days. Without food at 22° C, mice became torpid every day; the first period of torpor began in the dark, and the rhythm of oxygen consumption was thereafter reversed. At 10° C without food, mice failed to arouse to a normal metabolic rate every day; sometimes they were deeply hypometabolic for 48–56 hr. A circadian rhythm of reduced amplitude continued, however, and arousals to normal rate occurred approximately on multiples of 24 hr. Arousals continued to occur in mice without food at 10° C despite exposure to or state of animals under the following conditions: constant darkness with or without sound, air with 4.5% CO2, obesity, 9 months' prior conditioning to 10° C, 1,400 R acute whole-body gamma radiation. Mice acclimatized to 10° C had the shortest periods of normal metabolism and obese mice the longest. In P. longimembris (mean wt 10.7 g), P. inornatus (14.6 g) and P. formosus (20.5 g) at 10° C without food, frequency and extent of hypometabolism varied inversely with body weight.

A method for estimating the probability of an animal being in a particular region of the home range is discussed. Data for Perognathus longimembris (Coues) were used to illustrate the use of this method and were transform ed with r ′ = ( r λ − 1)/λ. One-sided tolerance limits were used to assert degrees of confidence γ that given percentages of the recaptures will be within specified distances from the estimated activity center.

A group of 160 female and 40 male captive pocket mice ( Perognathus longimembris ) were examined routinely for reproductive activity during January–June 1965. Limited observations were made throughout the summer and fall. Fifty-eight per cent of the females showed one or more estrous cycles during the routine inspection. Most exhibited polyestrus cycles of approximately 10 days duration. The incidence of first estrus was highest in March. Breeding was accomplished by pairing animals judged by external signs to be receptive. A total of 217 matings were attempted and 57 litters were produced. Five mice produced two litters each. Litters were born from late March through September. Males made sexually active with human chorionic gonadotropin sired several Utters. Information on hormone treatment, estrus, estrous cycles, postpartum and juvenile estrus, mating, gestation, maternal care and nest building is presented.

Rodent populations were studied during a 29-month period of crisis and recovery of food resources. Four species were abundant or common. Some of the elements of their biological success were observed: (1) Ecological stratification, e.g., Dipodomys merriami and Perognathus longimembris are both nocturnal herbivores, but the latter species is seasonally dormant; Onychomys torridus is a nocturnal carnivore, and Ammospermophilus leucurus is a diurnal herbivore. (2) P. longimembris was not captured during most of the fall and winter, apparently being dormant during this time. Dormancy of this small pocket mouse (8.5 g) probably accounts for its greater persistence; 30% of marked individuals survived from one spring to the next, as compared with 12–19% for D. merriami (37.5 g) which is active all year. (3) D. merriami is able to maintain a population density exceeding those of other nocturnal rodents, except P. longimembris , when this latter species is active. Densities of D. merriami ranged from 0.45 to 3.72 per hectare. Reproduction of D. merriami is correlated with winter rains and subsequent development of vegetation. Body weight increases during the winter months to a peak in early spring; reproductive activity follows the same pattern. Male kangaroo rats come into reproductive condition earlier than females, which may insure impregnation of early active females. Population densities of D. merriami vary with production of vegetation, with a considerable lag. The maximum density was observed about one year after the start of a drought period; low densities persisted for over one year after the vegetation had recovered. Home ranges of D. merriami tended to vary inversely with population density. Frequencies of capture were greatest when there was the most environmental stress. Activity tended to be greatest the first part of trapping nights. P. longimembris had greater home range and frequency of capture than D. merriami .

A technique for estimating the probability of interaction in space using the home range as a basis of measurement is presented. The overlap area between adjacent home ranges and the relative use of home range area are used to obtain the estimate. The methods were demonstrated with data for Perognathus longimembris (Coues) for the USAEC Nevada Test Site. Probable interaction between females ranged from .6301 for individuals with recapture centers only 11.43 m apart to .0000 for animals 88.53 m apart. In this case the recapture radius was 44.45 m. Probable interaction between males and females ranged from .6289 to .0000 with distances from recapture centers of 11.43 m to 85.53 m, respectively. Assumptions required by this technique and limitations of interpretation are discussed.

On October 15, 1950, Mr. Loraine Woodbury captured a specimen of Perognathus longimembris in a desert area known as Cedar Valley which lies to the west of Utah Lake in Utah County, Utah. The animal was caught by the tail in a snap trap and was brought into the laboratory alive. Strikingly contrary to the normal color of this species, which is predominantly buff overlaid with brown or black dorsally, the animal mentioned above was pure white except for a …

The little pocket mouse, Perognathus longimembris , was selected for a study of temperature regulation because (1) it is one of the smallest North American rodents (adult weight, 6.5 to 10 grams); (2) it is a member of the highly specialized family Heteromyidae; (3) it is locally very abundant; (4) it is readily maintained in captivity; and (5) nothing was previously known about its temperature regulation. Despite the abundance of pocket mice, very little has been published on the physiology of any member of the genus Perognathus . Hall (1946) adduced circumstantial evidence for the occurrence of hibernation in some species of pocket mice and its absence in others. Scheffer (1938) found that Perognathus parvus showed an irregular dormancy during the winter but he determined no body temperatures. We are unaware of any other published information concerning temperature regulation in the genus. P. longimembris occurs commonly in eastern and southern California, extreme northwestern Mexico, and throughout much of the Great Basin, reaching the northern limit of its distribution in southeastern Washington. It lives from below sea level in the Salton Sink to an altitude of at least 6500 feet in the Sierra Nevada. The present study was made between June and September, 1955, and is based on 23 adult animals trapped in the Antelope Valley and Walker Pass areas of the Mohave Desert of southern California. The captive animals were individually housed in glass jars or plastic boxes partly filled with fine sand. They were given no water and remained in excellent condition throughout the study on a diet of mixed bird seed. All temperatures were measured with 30 gauge copper-constantan thermocouples coated with baked insulating enamel and connected to a recording potentiometer. Oral and rectal temperatures were taken with thermocouples inserted to a depth of at least 2 cm.; …