Joyce E. Hofmann

Social organization in free-living prairie voles, Microtus ochrogaster

SummaryBreeding units (occupants of a nest including at least one reproductive female) within two free-living populations of the prairie vole, Microtus ochrogaster, were monitored by live-trapping at nest during two 28-h periods each week from October 1980 to March 1984. Data are presented for 281 breeding units from all seasons, at high and low population densities and during breeding and nonbreeding periods. Fifty percent of the breeding units were monogamous (single resident reproductive male and female), 27% consisted of a single reproductive female with no resident adult male and 23% included more than one resident adult male and/or female (“complex units”). Monogamous units were present in the same proportions during breeding and nonbreeding periods. The number of monogamous units was significantly greater at low population densities than at high densities. During winter there were relatively more complex units and fewer single female units than during the rest of the year. Monogamous pairs remained together for an average of 42 days. Seventy-eight percent of these pairs were disbanded by the death of one or both members. There were few overlaps of the home ranges of adjacent breeding units. Significantly more nests were visited by nonresident males than by females, and the intervals between visits by males were significantly shorter than those for visits by females. Males visited single female units significantly more often than units with one or more resident males. Survival of juveniles was generally very low; 38% and 34% of young males and females, respectively, that were trapped survived until 30 days of age. Of young females remaining at the natal nest at low population densities, only 17.6% were reproductively activated; 77.1% of such females became reproductively activated at high densities. All young females that dispersed from the natal nest became reproductive.

Natal dispersal and philopatry in prairie voles (Microtus ochrogaster) in relation to population density, season, and natal social environment

SummaryWe used intensive livetrapping to examine natal dispersal and philopatry in prairie voles (Microtus ochrogaster). The majority of male (70.0%) and female prairie voles (75.1 %) remained at the natal nest until death. Those males and females that did disperse left home at about the same age (45–55 days) and moved similar distances (28–33 m). Dispersal was more common (1) from small natal groups than from large natal groups, (2) following disappearance of parents, (3) during the breeding period than during the nonbreeding period, and (4) at low population densities than at high densities. Dispersal was not associated with level of competition for mates within natal groups, and dispersers did not differ from nondispersers in body weight. Our data do not support competition for mates or resources as important factors influencing natal dispersal in prairie voles. The absence of sex differences in dispersal tendency or distance, and our fording that more than half of dispersers had become reproductive before leaving the natal nest, lead us to suggest that inbreeding avoidance is not a primary function of dispersal in this species. Dispersal was, however, more common when potential mates within the natal group were relatives than when they were nonrelatives. Although not tested here, if family members avoid mating with one another through patterns of mate choice, then some animals may leave home in search of mates. The precise benefits associated with philopatry in prairie voles remain to be identified.

SIBLING RECOGNITION IN THE PRAIRIE VOLE, MICROTUS OCHROGASTER

Abstract Since mating is seldom observed between sibling prairie voles, Microtus ochrogaster, this, behavioural discrimination was used to investigate sibling recognition in this species. Cross-fostering of 1–3-day-old pups demonstrated that unrelated pups reared together did not breed, whereas siblings reared apart bred readily when paired at weaning. When unrelated voles were paired at 14 days of age, prior to sexual maturity, significantly fewer pairs bred than when strangers were paired at 21 days of age. Separation of 21-day-old siblings for 8 days before pairing overcame incest avoidance; a 15-day separation was required for breeding by siblings that had remained together until they were 50 days old. These results indicate that sibling recognition and, consequently, incest avoidance depend on association prior to weaning.

Social Organization and Mating System of the Prairie Vole, Microtus Ochrogaster

A communal nesting group, formed by additions to a monogamous pair breeding unit, is the basic year-round social unit of the prairie vole, Microtus ochrogaster. Before communal groups form, presumed monogamous pairs display traits normally associated with monogamy including cohabitation of a common nest, a shared home range, and dissolution of the pair primarily by mortality of one or both members. When juvenile nest mortality was reduced during late autumn-winter, extended-family groups formed. There was no difference in natal dispersal between summer and autumn-winter. Approximately 70% of the animals added to monogamous-pair breeding units were philopatric young. Unrelated adults (30% of the additions) joined extended-family groups in equal proportions in summer and late autumn-winter. Approximately half of the unrelated adults were reproductive when they joined an extended family group. During periods of winter reproduction most winter communal groups included at least one reproductive male and female, approximately half included two or more reproductive males and females (half of these were unrelated adults).

Natal dispersal and philopatry in prairie voles (Microtus ochrogaster): settlement, survival, and potential reproductive success

We analyzed the costs and benefits of natal dispersal and philopatry in a free-living population of the prairie vole, Microtus ochrogaster, in which 70% of the males and 75% of the females were philopatric. Rather than settling into a nest, 40% of male dispersers continued to wander throughout the study area, while only 13% of female dispersers did so. Whereas males were more likely to wander in spring-early autumn during low density periods, females were more likely to wander during spring-early autumn, irrespective of population density. Of those animals that settled into a nest, females were more likely than males to settle as single individuals. Same-sex siblings that dispersed commonly joined the same social group. Although often settling within 5 m of each other, opposite- sex siblings that dispersed never joined the same social group or formed a male-female pair. Total length of life was longer for males and females that dispersed than for those that remained at the natal nest. Animals survived lon...

Multiple exposures to adult males and reproductive activation of virgin female Microtus Ochrogaster

Virgin female Microtus ochrogaster living in family groups were reproductively activated by twelve 1-hr exposures over a 3-day period to unrelated sexually experienced males. Reproductive activation among virgin females receiving six or eight exposures over a 2- or 3-day period did not differ significantly from that of unexposed control females. Thus, frequent multiple exposures to unfamiliar males (and repeated stimulation by a male urinary chemosignal) can override the reproductive suppression typically experienced by virgin females remaining in family groups.

A survey for West Nile virus in bats from Illinois.

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.

Franklin's Ground Squirrel (Spermophilus franklinii) in Illinois: A Declining Prairie Mammal?

Abstract Franklins ground squirrel (Spermophilus franklinii) appears to be becoming increasingly uncommon in the eastern portion of its range, but current data on its status in Illinois are lacking. We conducted a mail survey of 166 wildlife professionals from throughout the historical range of the species in Illinois to obtain information pertaining to extant and extirpated populations and local population trends. Locations of potential populations were compared with 106 known historical points of occurrence. Twenty-six sites were chosen for livetrapping surveys to confirm the presence or absence of the species. We considered it likely that Franklins ground squirrels might persist in these sites due to information provided in the mail survey and/or known historical occupancy. Franklins ground squirrels inhabited only 3 of the 26 trapping sites; however, we located two other areas of probable occurrence in addition to the locations that we surveyed. While it is clear that Franklins ground squirrel has declined in Illinois, the magnitude of this decline remains unknown due to the secretive behavior of the species and a lack of knowledge about its ecology. The methods described in this paper are an efficient means of collecting initial information concerning the status of a species that is difficult to observe or about which little is known.

Effect of Multiple Short-Term Exposures of Pregnant Microtus ochrogaster to Strange Males

Bruce (1959, 1960) discovered that exposure of female laboratory mice to unfamiliar males within 24 h of coitus inhibited implantation and blocked pregnancy. Females experiencing pregnancy failure returned to estrus 4-5 days after the original mating (Bruce, 1960). This pre-implantation pregnancy block, or Bruce effect, was subsequently observed in wild house mice, Mus musculus (Chipman and Fox, 1966); deer mice, Peromyscus maniculatus (Eleftheriou et al., 1962); field voles, Microtus agrestis (Clulow and Clarke, 1968); meadow voles, M. pennsylvanicus (Clulow and Langford, 1971); and prairie voles, M. ochrogaster (Stehn and Richmond, 1975). Post-implantation termination of pregnancy following exposure to strange males has been found in P. maniculatus, M. pennsylvanicus, and M. ochrogaster (Kenney et al., 1977; Stehn and Richmond, 1975). The incidence of pregnancy failure was greater for M. ochrogaster than for the other two species (Kenney et al., 1977). In M. ochrogaster a reduced incidence of pregnancy termination was not apparent until more than 15 days of gestation had elapsed (Stehn and Richmond, 1975). In the above studies occurrence of pregnancy block or termination was determined by separating a pair that had mated and exposing the female to a strange male for prolonged periods ranging from one to several days. Pregnancy termination could occur naturally in pair-bonded species if a pregnant female lost her original mate and subsequently acquired a new one. Pregnancy failure might also occur in such species as the result of brief exposures to strange males. Chipman et al. (1966) found that multiple short-term exposures to a strange male were as effective as continuous exposure in causing pregnancy failure in recently inseminated female laboratory mice. The present study was designed to determine the effect of multiple short-term exposures to strange males on M. ochrogaster females at different stages of pregnancy (2, 5, and 10 days after mating). Since M. ochrogaster has a pair-bonded, monogamous mating system (Getz et al., 1981; Getz and Hofmann, 1986), the presence of the male during pregnancy might influence whether pregnancy block or termination occurred. Therefore, two experiments were performed; in one the females mates were permanently removed prior to introduction of strange males; in the other, the mates were housed with the females throughout pregnancy. All experimental voles were laboratory reared from stock obtained near Urbana, IL; the animals had been in captivity for 4-5 generations. The breeding colony and experimental animals were maintained at 24?C under a 15L:9D light cycle. Voles were housed in 24 by 45 cm plastic breeding cages (except as noted below) with wood-chip bedding; Purina rabbit chow and water were provided ad libitum. Only nulliparous females were used because lactating females mated during post partum estrus could have a different susceptibility to pregnancy block due to the influence of prolactin (Bruce and Parkes, 1960, 1961; Mallory and Clulow, 1977). Virgin females were brought into estrus by the following procedure. After separation from their parents at 21 days of age, voles were housed in sibling groups; females do not come into estrus when maintained with siblings (Carter et al., 1980). At 45-50 days of age, males were removed and placed individually in 17 by 28 cm cages. Three days later a non-littermate female was placed in the cage of each male. Each pair remained together for approximately 5 h after which the males were moved to clean 24 by 45 cm cages, while the females were left in the soiled cages. On the following day each female was placed in the cage of the same male for 1 h and the pair observed to determine if they mated. If mating did not occur the pair was separated, the female remaining in the cage that had been occupied by the male. These pairs were placed together and observed for 1-h periods during the following 2-3 days. Vol. 68, No. 1 166

TEMPORAL VARIATION IN BAT WING DAMAGE IN THE ABSENCE OF WHITE-NOSE SYNDROME

Abstract 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.