We examine factors affecting the winter range limit of a migrating mammal, the silver-haired bat (Lasionycteris noctivagans), in states surrounding Lake Michigan, the fourth largest freshwater lake in the world. Using 555 citizen-based captures gathered between 1977 and 2016, we show that silver-haired bats overwinter (December–February) as far north as the 45th parallel, in areas roughly demarcated by the −12.2 °C (10 °F) mean daily minimum isotherm for January. Although summering populations adjacent to the lake are dominated by males, wintering animals are predominantly female and presumably migrants from north of Lake Superior. Logistic regression suggests that silver-haired bats are more likely to overwinter in warm areas, in counties near the lake, in urbanized locales, and on the west side of the lake. We believe that these small-bodied, solitary bats are hibernating in buildings and that use of human-made structures has allowed the silver-haired bat to overwinter in regions that are devoid of mines, caves and rock crevices and that are too cold for successful hibernation in trees. Lake Michigan impacts where this animal overwinters, presumably through the moderating influence of the lake on multiple aspects of the surrounding climate and because the shoreline likely is a major migratory pathway.

White-nose syndrome (WNS) is an emerging infectious wildlife disease that has killed more than 5 million bats in the eastern United States since its discovery in winter 2006. The disease is associated with a cold-adapted fungus that infects bats during winter hibernation. Wing damage has been documented in bats with WNS and could become a useful screening tool for determining whether samples should be submitted for testing. However, because there are no historic records, to our knowledge, of wing damage before the emergence of WNS, it is unknown what types of grossly observable wing damage, if any, are specific to WNS. To address this knowledge gap, we inspected the wings of 1,327 bat carcasses collected in Illinois from 2005 and 2008-2010, then used Akaike information criterion to evaluate generalized linear models of the frequencies of different categories of wing damage using age, sex, year, and season as predictors in big brown bats (Eptesicus fuscus). Wing discoloration was best predicted by year and season. There were no clear predictors for other categories of wing damage. We found that about one-fourth of big brown bats surveyed from this presumptive WNS-negative sample had moderate or severe wing damage. We encourage further studies of the relationship between WNS and wing damage to better understand which categories of damage are to be expected in the absence of WNS in susceptible species.

Populations of 2 species of arvicoline rodents, the prairie vole (Microtus ochrogaster) and meadow vole (M. pennsylvanicus), were monitored monthly in alfalfa bluegrass, and tallgrass prairie habitats in east-central Illinois from 1972 through 1997. Alfalfa provides very high-quality preferred food and poor vegetative cover for both vole species, whereas bluegrass provides intermediate food and vegetative cover. Preferred food resources were very low, especially for M. ochrogaster, and vegetative cover was very dense in tallgrass prairie. Maximum and mean population densities of M. ochrogaster were highest in alfalfa, intermediate in bluegrass, and lowest in tallgrass prairie. Populations of M. ochrogaster displayed synchronous 3- to 4-year multiannual cycles in all 3 habitats. Cycles were most pronounced in alfalfa, less pronounced in bluegrass, and barely discernible in tallgrass prairie. Food availability seems more important than vegetative cover for the success of M. ochrogaster. Densities of M. pennsylvanicus generally were very low in bluegrass and alfalfa habitats, both of which contained an abundance of preferred food plants. When M. pennsylvanicus was present in abundance in these 2 habitats, populations displayed annual or erratic fluctuations. Densities of M. pennsylvanicus were much higher in tallgrass prairie than in the other 2 habitats. Although vegetative cover seems more important than food availability for the success of M. pennsylvanicus, no evidence existed for population cycles in tallgrass prairie. We found no synchrony among population fluctuations of the 2 species of voles in the 3 habitats.

We tested for differences in the proportion of reproductively active males and females, proportion of the population composed of young and immigrants, and monthly survival (total, adult, young) among phases (trough, increase, and decline) and among habitats (alfalfa, bluegrass, and tallgrass) of 30 population fluctuations ofMicrotus ochrogaster Wagner, 1842 over 25 years in east-central Illinois USA. Total population survival and survival of adults and young were greatest during the increase phase, among fluctuations, irrespective of habitat. The proportion of reproductively active adult males and females was lowest during the decline phase, an effect of lower reproduction during the winter. These results suggest that phase-specific changes in survival were the primary demographic factor driving population fluctuations ofM. ochrogaster in our study sites. We conclude that small-scale spatially different population fluctuations may be explained by the same mechanisms that explain fluctuations within a population.

Effects of 74 episodes of extreme weather on stoppage of population growth and resulting amplitudes of annual population fluctuation of 39 fluctuations of Microtus ochrogaster and 20 fluctuations of M. pennsylvanicus were studied over a 25 y period in east-central Illinois. Episodes of extreme weather may have stopped population growth of only six M. ochrogaster fluctuations and of two M. pennsylvanicus fluctuations. Cessation of growth of only one population fluctuation (M. pennsylvanicus) could be attributable solely to an episode of extreme weather. Episodes of extreme weather occurred during 62% of the increase phases of M. ochrogaster population fluctuations and 75% of those of M. pennsylvanicus, with no associated cessation of population growth. We conclude that episodes of extreme weather were not a primary factor responsible for cessation of population growth or variation in amplitudes of population fluctuations of either M. ochrogaster or M. pennsylvanicus.

We conducted removal experiments in open populations of Microtus ochrogaster and M. pennsylvanicus to test for potential interspecific competition between coexisting populations in bluegrass and tallgrass prairie in east-central IL, USA. Population densities of M. ochrogaster and M. pennsylvanicus in bluegrass were not suppressed by presence of the other species. In bluegrass, presence of the other species did not negatively influence monthly survival, persistence of young on the site, reproduction, or number of immigrants of either M. ochrogaster or M. pennsylvanicus. Although M. pennsylvanicus appeared to exert a strong suppressing effect on population densities of M. ochrogaster in tallgrass and limited the number of immigrants, survival, persistence of young, and proportion reproductively active female M. ochrogaster were not negatively affected by presence of M. pennsylvanicus. We conclude that interspecific competition did not play a major role in driving dynamics of coexisting populations of M. ochrogaster and M. pennsylvanicus in our study sites [Acta Zoologica Sinica 53 (5): 800–811, 2007].

We studied factors affecting peak densities and amplitudes of fluctuation during 20 annual population fluctuations of Microtus pennsylvanicus Ord, 1815 in alfalfa and bluegrass habitats over a 25-year period. Survival was correlated with population density over the 25 years and was the most consistent variable associated with stoppage of population growth. Although not correlated with population density over the 25 years, a decline in the proportion of reproductively active adult females contributed to cessation of growth of population fluctuations that peaked in late autumn-winter, and to cessation of growth of eight of eleven population fluctuations that peaked during summer-early autumn. We conclude variation in survival to be the primary factor affecting peak densities and amplitudes of population fluctuation of M. pennsylvanicus .

A blocking enzyme-linked immunosorbent assay was used to test 97 serum samples from big brown bats (Eptesicus fuscus) captured in six counties in Illinois between May 2002 and February 2004 for West Nile virus (WNV) antibodies. One female big brown bat tested positive for WNV antibodies. Samples of kidney, liver, and heart tissue were collected from 312 bats of seven species that were submitted to the Illinois (USA) Department of Public Health or the Illinois Department of Agriculture diagnostic laboratories between January 2001 and December 2003. Tissue samples were tested for WNV using TaqMan reverse transcriptase polymerase chain reaction and all were negative. Prevalence of WNV antibodies in the bats (1%) was lower than previously reported for other flaviviruses, but similar to the prevalence (2%) of WNV antibodies reported in bats from New Jersey and New York, USA. Additional research is needed to determine potential impact of WNV infections on bats and to determine whether they play a role in the WNV transmission cycle.

Factors influencing initiation of population fluctuations of Microtus pennsylvanicus were studied in alfalfa and bluegrass habitats for 25 years. Increased survival during spring and summer appeared to be the most important factor associated with initiation of a population fluctuation. The proportion of reproductively active adult females did not influence initiation of population fluctuations. The interval between fluctuations was not correlated with density of the previous population fluctuation. We propose that population fluctuations were initiated by the net effects of relaxation of predation pressure of multiple generalist predators, which occurred erratically across years.

Utilizing data obtained at 3.5-d intervals for a population of Microtus ochrogaster, we compared efficacy of monthly and semi-monthly mapping of small mammal populations in respect to frequency of change of population density, survival and proportion adult females that were reproductively-active. For all three variables, both monthly and semi-monthly intervals closely tracked the 3.5-d intervals. The main exception was the monthly intervals under-recorded by 20% the peak density of one of four population fluctuations during the study; the semi-monthly intervals tinder-recorded the highest peak density by 4%. Overall, efficacy of a monthly monitoring protocol appeared adequate to describe the three demographic variables and differed little from that of a semi-monthly protocol. Consequently, the additional time and resources required for a semi-monthly trapping protocol do not appear warranted.

JENNIFER M. MENZEL,1 U.S. Forest Service, Northeastern Research Station, Parsons, WV 26287, USA W. MARK FORD, U.S. Forest Service, Northeastern Research Station, Parsons, WV 26287, USA MICHAEL A. MENZEL, Alston & Bird, LLP, Atlanta, GA 30309, USA TIMOTHY C. CARTER, Southern Illinois University, Carbondale, IL 62966, USA JAMES E. GARDNER, Missouri Department of Conservation, Jefferson City, MO 65102, USA JAMES D. GARNER, Illinois Department of Natural Resources, Springfield, IL 62702, USA JOYCE E. HOFMANN, University of Illinois Museum of Natural History, Champaign, IL 61820, USA

We studied the influence of preferred food, forbs, and vegetative cover on survival and reproduction at different population densities of Microtus ochrogaster and M. pennsylvanicus in alfalfa, bluegrass, and tallgrass prairie habitats in east-central Illinois for 25 years. Population densities of M. ochrogaster were greatest in alfalfa, least in tallgrass, and intermediate in bluegrass, whereas those of M. pennsylvanicus were greatest in tallgrass, least in alfalfa, and intermediate in bluegrass. For both species, preferred food availability was greatest in alfalfa, intermediate in bluegrass, and least in tallgrass. Vegetative cover was relatively sparse in alfalfa, especially in winter, and dense throughout the year in bluegrass and tallgrass. Variation in survival emerged as the most important factor explaining population differences between the 2 species. Reproduction had little differential impact on abundance of either species in any of the 3 habitats. Survival of M. ochrogaster was higher in alfalfa than in bluegrass or tallgrass; survival of M. pennsylvanicus was higher in tallgrass than in alfalfa or bluegrass. Differential survival among habitats and between species was influenced primarily by amount of vegetative cover. We suggest that M. ochrogaster is less susceptible than M. pennsylvanicus to predation by raptors and large carnivores (predators that hunt from above vegetative cover), whereas M. pennsylvanicus is less susceptible than M. ochrogaster to snakes and small carnivores (predators that hunt under vegetative cover).

Abstract We studied factors influencing home-range size in fluctuating populations of Microtus ochrogaster and M. pennsylvanicus in alfalfa, bluegrass, and tallgrass habitats over a 25-year period in east-central Illinois. Preferred food availability for both species was greatest in alfalfa and least in tallgrass, lesser during winter than other seasons in all 3 habitats, and greater in alfalfa during winter than in the other 2 habitats. Vegetative cover was sparse, especially during winter, in alfalfa and dense year-round in bluegrass and tallgrass. Movement distances of M. ochrogaster tended to be smaller in alfalfa than in bluegrass and tallgrass; movement distances of neither vole species differed between bluegrass and tallgrass. Within alfalfa, movement distances of both species were smaller during winter, when cover was sparse and food availability low. No seasonal difference was found in movement distances of either species within bluegrass and tallgrass, where cover was dense year-round, but food availability was low during winter. Movement distances of M. ochrogaster were not affected by supplemental feeding in bluegrass and tallgrass; those of M. pennsylvanicus were smaller in supplementally fed tallgrass. We conclude that cover, as an indicator of risk of predation, influenced home-range sizes of both species more than did food availability.

We studied the influence of immigration on the dynamics ofMicrotus ochrogaster Wagner, 1842 andM. pennsylvanicus Ord, 1815 populations in alfalfa, bluegrass, and tallgrass prairie in east-central Illinois for 25 years. The numbers of immigrants in a site were positively correlated with overall population densities of the species in the vicinity of the study sites and within the study site. Population density of the other species was not correlated with immigration of either species. Immigrants did not differ significantly from residents with respect to sex-ratio and reproductive condition. Persistence of immigrantM. pennsylvanicus was lower than that of resident adults in all three habitats, while that of immigrantM. ochrogaster was lower than that of resident adults in alfalfa, where the species was most abundant. Neither the absolute number of immigrants nor the proportion of the population composed of immigrants indicated an effect of immigrants on among- and within-habitat differences in demography and population fluctuations of either species. Immigrants may have been an important factor in maintenance ofM. pennsylvanicus in alfalfa, a low-quality habitat, but the influence of immigration on the dynamics of populations inhabiting other habitats was insubstantial.