Effect of body mass on hibernation strategies of woodchucks (Marmota monax).

The benefits of mammalian hibernation have been well documented. However, the physiological and ecological costs of torpor have been emphasized only recently as part of a hibernation-optimization hypothesis. This hypothesis predicts that hibernators with greater availability of energy minimize costs of torpor by less frequent utilization of torpor and by maintaining higher body temperatures (T(b)) during torpor. In order to further examine the relationship between body mass and other parameters of hibernation, we present data, collected over a 12-year period, on the hibernation patterns of free-living woodchucks (Marmota monax) in southeastern Pennsylvania. Body mass was positively correlated with T(b) and negatively correlated with percentage of the heterothermic period spent in torpor. Thus, woodchucks with greater mass exhibited less time in torpor as a proportion of their heterothermic period and at higher T(b) than those with lesser mass. This strategy potentially enhances the physiological and physical ability of woodchucks to defend territories, avoid predation, find mates, and complete the reproductive cycle upon emergence from hibernation. Our results further support the hibernation-optimization hypothesis by demonstrating the relationship between body mass and characteristics of torpor and contributing toward a fuller understanding of this concept.

Relationship between blood mercury levels and components of male song in Nelson's sparrows (Ammodramus nelsoni).

Mercury (Hg) adversely affects the health and behavior of exposed wildlife; however, behavioral effects remain largely unknown. Changes in avian singing behavior may affect a male's fitness because song reveals male quality and thus influences female mate choice and male territory-holding ability. Nelson's sparrows (Ammodramus nelsoni) live exclusively on salt marshes and risk high levels of Hg exposure and bioaccumulation. We recorded songs of male Nelson's sparrows at two locations with different Hg exposure to determine if total blood Hg concentration was related to song characteristics, as previously reported for other species. Males with higher blood Hg levels sang at higher maximum tonal frequency, but blood Hg and site location did not influence low tonal frequency and bout duration, contrary to predictions based on other species. Within the contaminated site, Hg levels were related to bouts per minute and gap duration, such that males at that site sang faster songs. Hg influences hormones and alters brain development, raising questions about specific effects on the brains and singing behavior of male Nelson's sparrows.

Intraspecific variation in space use, group size, and mating systems of caviomorph rodents.

Intraspecific variation in social systems is widely recognized across many taxa, and specific models, including polygamy potential, resource defense, and resource dispersion, have been developed to explain the relationship between ecological variation and social organization. Although mammals from temperate North America and Eurasia have provided many insights into this relationship, rodents from the Neotropics and temperate South America have largely been ignored. In this review we focus on reports documenting intraspecific variation in spacing systems, group size, and mating systems of caviomorphs. This large group of New World hystricognath rodents occupies a diverse array of habitats; thus, members of the same species potentially exhibit different social systems in response to different ecological conditions. Spatial patterns vary in response to a diverse array of factors, including predation, food availability, population density, and soil characteristics. Changes in group size typically correlate with changes in resource availability, particularly food. Mating systems generally reflect the ability of males to control access to females, which may depend on population density or food distribution. In general, social organization in caviomorphs fits predictions of resource-based models; however, most studies have been purely observational, involving small numbers of animals over short time periods and reporting qualitative rather than quantitative levels of ecological correlates. In future studies the use of molecular techniques and controlled, experimental manipulations can increase our understanding of intraspecific variation in caviomorph social systems. This understudied group of rodents offers excellent opportunities to provide insights into the influence of ecological conditions on behavior such as social systems.

Latitudinal differences in the hibernation characteristics of woodchucks (Marmota monax).

There is little information on the phenotypic flexibility of hibernation characteristics within species. To address this issue, we observed differences in hibernation characteristics of three free-ranging populations of woodchucks (Marmota monax) distributed along a latitudinal gradient from Maine to South Carolina. Data from free-ranging animals exhibited a direct relationship between latitude and length of the hibernation season. As expected, woodchucks in the northern latitudes hibernated longer than those in the southern latitudes. Also, the length of interbout arousals decreased with increase in latitude, whereas the length of torpor bouts and the number of arousals increased. Thus, we observed phenotypic plasticity in hibernation characteristics based primarily on latitudinal temperature differences in each population. Further analysis revealed a direct relationship between latitude and total time spent in torpor. Maine animals spent 68% more time in torpor than South Carolina animals. However, total time spent euthermic did not differ among the three populations. The "cost-benefit" hypothesis of hibernation may help to explain these results. It assumes that hibernators avoid the physiological stress of torpor by staying euthermic as much as possible. Woodchucks in each population maximized time spent euthermic, utilizing torpor only at the level needed to survive winter hibernation and to commence reproduction in the spring.

Effects of immunocontraception on behavior in fallow deer (Dama dama).

Immunocontraceptives can control growth in wild and captive populations; however, in doing so, they should not disrupt species-typical behavior patterns. The presence of treated females could disrupt social interactions in a population; yet, few studies have examined effects of immunocontraception on behavior. The goal of this project was to determine whether behavior in a fallow deer (Dama dama) population vaccinated with porcine anti-zona pellucida (pZP)-immunocontraceptives differed from behavior in a population of unvaccinated deer. We predicted that pZP-treated females would spend a higher percentage of time exhibiting mating and dominance behavior than nontreated females, and that males interacting with pZP-treated females would spend a higher percentage of time demonstrating mating and aggressive behavior than males interacting with nontreated females. We recorded activity budgets of males and females in two fallow deer populations, one pZP-treated and the other untreated, before, during, and after rut. Females did not differ in time spent displaying mating or dominance behavior compared to nontreated females. Males coexisting with nontreated females spent more time exhibiting aggressive behavior during rut than males living with pZP-treated females, but males did not differ in time spent in mating behavior. Thus, immunocontraception did not seem to affect behavior adversely. However, sample sizes, living conditions, and sex ratios may have affected the results. Given these limitations, future research is needed to confirm our findings. Zoo Biol 27:49-61, 2008. (c) 2007 Wiley-Liss, Inc.