Reportamos os resultados de inventários de pequenos mamíferos conduzidos na região de Jaíba, norte de Minas Gerais, sudeste do Brasil, entre 1990 e 1995. Essa região está localizada no limite sul do bioma Caatinga, e abriga um conjunto único de ecossistemas naturais e extensas áreas cultivadas. Com um esforço total de 2964 armadilhas-noite e 44 sessões de captura com redes de neblina, nós capturamos 893 pequenos mamíferos, que permitiram a identificação de 46 espécies, incluindo quatro marsupiais, 13 roedores e 29 morcegos. Nós reportamos espécies endêmicas da Caatinga (Wiedomys pyrrhorhinos e Xeronycteris vieirai) e espécies que são novas para a fauna de mamíferos de Minas Gerais (Tonatia saurophila, X. vieirai e Myotis lavali). Nós também fornecemos o primeiro registro válido, com material testemunho, de Micronycteris sanborni para o sudeste do Brasil, e estendemos a distribuição geográfica conhecida de X. vieirai em 800 km na direção sul. Todos os morcegos destacados aqui como endêmicos ou representando novos registros estiveram associados a afloramentos de calcário, sugerindo que a preservação deste tipo de hábitat pode ser particularmente relevante para conservação desses mamíferos.

We report the results of small mammals inventories conducted in the region of Jaíba, northern Minas Gerais state, southeastern Brazil, from 1990 to 1995. This region is located in the southern limit of the Caatinga biome, and harbors a unique set of natural ecosystems and extensive agricultural areas. With a total effort of 2964 trap-nights and 44 net sessions, we captured 893 small mammals from 46 species, including four marsupials, 13 rodents, and 29 bats. We report on species that are endemic to the Caatinga (Wiedomys pyrrhorhinos and Xeronycteris vieirai), and species that are new to the mammal fauna of the state of Minas Gerais (Tonatia saurophila, X. vieirai, and Myotis lavali). We also provide the first valid voucher-supported record of Micronycteris sanborni from southeastern Brazil, and extend the known range of X. vieirai 800 km southward. All bats highlighted here as endemic or representing new records were associated to limestone outcrops, suggesting that preservation of this kind of habitat may be particularly relevant to the conservation of these mammals.

Introduction: We analyzed the variation in the age structure, sex ratio, proportion of reproductive individuals, age and size at sexual maturity, and litter size in a population of the sigmodont rodent Wiedomys pyrrhorhinos. We compared the observed distributions with the monthly rainfall for the same period, to identify the reproductive period and to assess the effects of the rains on the age structure of the population during the ensuing months. We further compared our results with age structure patterns recovered from other documented rodent outbreaks to identify possible causes of a presumptive population outbreak represented by this series. Methodology: Museum samples had been obtained between July 1953 and February 1955 from 40 sites in Caruaru, Pernambuco, Brazil (Fig. 1, Appendix). Records from a total of 2,280 individuals, 1,834 of which represented by their skulls, were analyzed. Skulls were sorted into seven age classes based on molar eruption and wear (Fig. 3). Monthly rainfall during the entire collecting period (Fig. 2) was analyzed for putative correlations with monthly frequencies of specimens (Figs. 4 and 5) and of indicators of reproductive condition, tabulated for each sex and age class. Results: Monthly frequency distributions of age classes presented separated and consecutive modal peaks, conforming to an age structured population (Fig. 6). Monthly proportions of pregnant females were highly correlated with the amount of rainfall of the same and of the previous month (Fig. 7), although records of pregnant females were obtained every month between July 1953 and December 1954. Pregnant females were found from age class 2 on. From January to April, 1954, reproductive females belonged to age classes 5 to 7. From May to September a wide range of age classes was documented among pregnant females, and from October to December only those of age classes 2 to 4 were recorded (Fig. 8). Litter size varied throughout the year, with larger averages and ranges at mid-wet season (June-August) (Fig. 10) and was highly correlated with female weight, female length and with the amount of rainfall of the previous 30 days. Higher means in litter size were also in phase with higher proportions of pregnant females and with the age class 1 peak. Discussion and Conclusion: The population peak occurred four to six months after the rainfall peak (September - November) and was primarily comprised of young adults. After this period, the pregnancy rates were very low, ceasing completely by January, 1955, when most of the individuals belong to older age classes. This shift in age structure from younger to older individuals during population decline indicated that the samples documented an outbreak episode in 1954. This episode was possibly related to the unusual rainfall in November 1953, apparently sufficient to support two closely-spaced breeding seasons, with the second amplifying the effect of the first.

Hemos analizado la variación en la estructura etaria, proporción sexual, proporción de individuos reproductivos, edad y grado en la madurez sexual, y el tamaño de la prole en una población del roedor sigmodontino Wiedomys pyrrhorhinos, con base en una gran serie de individuos obtenida entre julio de 1953 y febrero de 1955 en Caruaru, Pernambuco, Brasil. Se registraron 2,280 individuos, de los cuales 1,834 están representados por cráneos, los que fueron analizados. Los cráneos fueron agrupados en siete clases de edad basadas en la erupción y desgaste molar. La proporciones mensuales de hembras grávidas tuvieron una alta correlación con la cantidad de lluvia del mismo mes y del mes anterior, a pesar de que la variación han sido encontradas también durante la estación seca. El tamaño de la prole varió a lo largo del año, con valores más altos durante mediados de la estación húmeda (junio), y este fue altamente correlacionado al peso, el largo del cuerpo de la hembra y con la lluvia de los 30 días anteriores. Distribuciones de frecuencias mensuales de clases de edad presentaron máximos modales consecutivos y separados, ajustándose a una población estructurada de manera etaria. El máximo poblacional ocurrió de 4 a 6 meses después del máximo de lluvias (septiembre-noviembre) y estaba compuesto primariamente por jóvenes adultos. A partir de ese período, sin embargo, las tasas de gravidez fueron muy bajas, cesando completamente en enero, cuando la mayoría de los individuos pertenecía a clases etarias más viejas. Ese cambio en la estructura etaria, de los más jóvenes a individuos más viejos durante el descenso poblacional, indicó que la muestra disponible sufrió un surto poblacional en 1954. Este episodio fue posiblemente relacionado a un aumento poco común en las lluvias en noviembre de 1953, aparentemente suficiente para soportar dos estaciones reproductivas enmendadas.

Myotis albescens (É. Geoffroy, 1806) occurs from Mexico to Uruguay and Argentina. Despite a large number of specimens in collections, its variability in South America has been underestimated, potentially leading to errors in identification. In order to clarify the taxonomic limits of M. albescens and to evaluate previous hypotheses of geographic variation in size we analyzed the type material and studied the variability in South American samples using multivariate exploratory and confirmatory procedures, as well as frequency analyses of discrete morphological data. The presence of a fringe of hairs along the trailing edge of the uropatagium, the long and silky pelage with frosted appearance on the dorsum, ear 9 to 14 mm long, broad interorbital and postorbital constrictions, and a globular braincase were identified as the most useful traits to distinguish M. albescens from its South American congeners. In agreement with Bergman's rule, larger specimens were found in the South. Beyond the geographic component, Individual variation is an important factor affecting the variability in the size and shape of the skull and pelage color.