Russell Davis

Island Biogeograhy of Montane Forest Mammals in the American Southwest

Information from packrat (Neotoma spp.) middens and other paleoenviron- mental indicators was used to reconstruct Pleistocene distributions of macrohabitats in the American Southwest (Arizona, New Mexico, and southern Utah and Colorado). This revealed a system of southern montane forests that were isolated during the Pleistocene (primarily by woodlands) as well as today (by grasslands, chaparral, and desertscrub). Based on the presence of at least five species of nonvolant forest mammals on these montane islands, we inferred that these mammals immigrated across woodlands during the Pleis- tocene. Because the great majority of montane forests in the American Southwest are now isolated by woodlands, but not grasslands, chaparral, or desertscrub, we hypothesized that post-Pleistocene immigrations may influence the structure of mammalian communities on these montane islands. This hypothesis was supported by the highly significant correlation of mammalian species richness with current isolation as well as area (P < .01 for simple correlations and for partial correlations after removing effects of latitude and area or isolation: 26 species, 27 islands). When isolation was partitioned into distance to be traveled across woodland vs. grassland-chaparral habitats, species richness was significantly correlated with the latter measure of isolation (P < .01) but not with the former, indicating that woodlands do not represent major barriers to immigration. Seventeen of 26 species considered are reported with at least 10% of their record locations in woodlands and other low-elevation habitats. Analyses of patterns of occurrence of seven species of forest mammals inhabiting between 7 and 16 islands revealed that insular distribution was significantly (P < .01) affected by area in two species, by area and isolation in three species, and by isolation alone in the remaining two species. Based on our reconstruction of Pleistocene macrohabitat distributions, analyses of community- and species-level patterns, and evidence on the ability of forest mammals to inhabit and disperse across woodlands and other low-elevation habitats, we conclude that community structure of montane forest mammals in this region of the American Southwest is influenced by post-Pleistocene immigrations as well as extinctions.

Flight Speeds in Western Bats

By using a simulated mine tunnel, the average speed and individual variation of 17 western bats were determined. Eptesicus fuscus showed the maximum speed of those tested (15.5 mph), whereas Pipistrellus hesperus showed the minimum value (4.8 mph). In many species speed of flight is correlated with the size of the bat.

Growth and Development of Young Pallid Bats, Antrozous Pallidus

In southern Arizona, young pallid bats are bom in mid-June. the average juvenile has reached the adult range of forearm size by the fifth week of age, and almost all are within adult range by the seventh week. the body weights of the young of both sexes, however, are significantly less than those of the adults until after autumn of the first year, and yearling females weigh significantly less than adults through the autumn of their second year. Development of young pallid bats in wild populations apparently proceeds through several stages at a faster rate than that of young bats reared in captivity. Forearm measurement provides a usable means of estimating ages of the younger bats. by the combined use of forearm measurement and observation of certain developmental stage “check points,” rough estimates of age can be made at least until adult conditions are reached. the use of a checklist of features allows the young of the year to be distinguished from the adults through late fall of the first year. Pallid bats show no sexual dimorphism in forearm lengths, and the young show none in body weight until about the end of the first year of age. Yearling females normally give birth to only one young, whereas most older females give birth to two. Young males are not sexually active in their first autumn and probably not during their first year. Adult females nurse only the young to which they have given birth.

Montane mammals of the American Southwest: the possible influence of post-Pleistocene colonization

Insular biogeographical theory was used to analyse the current assemblages of forest-dwelling species of small, non-flying mam- mals on the mountains of New Mexico and adjacent parts of Arizona. These montane islands of forest habitat are surrounded by woodlands and grasslands, without major intervening desert scrub barriers to north-south colonization. The source of the species included in the analysis was assumed to be the southern extension of the Rocky Mountains in northern New Mexico. Three variables were included in this analysis: species rich- ness, area and isolation (as estimated by two measures of distance from the source). In multiple regression analysis, both area and isolation were found to have significant contributions to the variation in the numbers of species on these montane islands. Similar results were also obtained from an analysis of data from the literature for a larger region of the American Southwest. These results, which differ from those for montane species assemblages in the Great Basin, suggest that the present distributions of mammals on mountains in New Mexico and adjacent parts of Arizona have been influenced by the combined effects of post-Pleistocene colonization as well as vicariant events and subsequent extinctions.

An example of contemporary colonization of montane islands by small, nonflying mammals in the American southwest

The yellow-nosed cotton rat (Sigmodon ochrognathus) is a montane specialist that occupies mainly oak-pinon-juniper and higher-elevation habitats. Its present pattern of distribution in southern Arizona and southwestern New Mexico indicates an extension of range northward from the eastern slopes of the Sierra Madre Occidental by expansion through continuous, montane, woodland habitat and by the contemporary colonization of one isolated mountain from another by crossing grassland gaps. Collection records indicate that this northward expansion has occurred in Arizona and New Mexico during the past 50 years and that it is continuing today.

Repeated Homing Exhibited by a Female Pallid Bat

A pallid bat (Antrozous pallidus) returned home from eight consecutive releases from six distinctly different directions and from distances ranging from 21 to 68 miles. This performance indicates that chance alone cannot be a major factor in homing, and that certain abilities possessed by this bat, and not simply randomness, must have been in operation.

Reproductive Tract and Evolutionary Relationships of the Chinese Rock Squirrel, Sciurotamias davidianus

The male reproductive tract and female os genitale of the endemic Chinese rock squirrel Sciurotamias davidianus are described for the first time. The presence of a penile duct, a well-developed baculum, and accessory glands separates Sciurotamias from the tribe Tamias-ciurini, and the structure of the baculum also separates it from the Callosciurini. The penis, baculum, and certain other characters are unexpectedly similar to those of the giant Indo-Chinese tree squirrels, Ratufa ; thus Sciurotamias is referred tentatively to the tribe Ratufini.