Premating behavioral tactics of Columbian ground squirrels

In polygynous and polygynandrous mating systems males possess a variety of behavioral tactics that increase their access to reproductive females. In addition to overt combat or defending resources that attract mates, males use premating tactics that provide them with subsequent opportunities to copulate with receptive females. For Columbian ground squirrels, Urocitellus columbianus, we report that co-occupation of a burrow system by a reproductive male and a female on the night before the female exhibits diurnal estrus is an example of such a tactic. Our hypothesis was that nocturnal underground association results in successful consortships and therefore constitutes a mating tactic that is complementary to other mating behaviors exhibited during a female's estrus. Under this hypothesis appropriate predictions are that: males co-occupying a burrow system with a female at night should mate first with that female; males co-occupying a burrow system with a female overnight should sire more of her offspring than her subsequent mates; and the reproductive success of males co-occupying a burrow system with females should be higher than the reproductive success of mates that do not. To test our predictions we used a combination of field observations on nocturnal underground consortships (NUCs) and microsatellite DNA analyses of paternity. Males copulated with females during NUCs, as evidenced by inseminations. These males sired more offspring than males that did not participate in NUCs. Males ≥3 years old participated in more NUCs than sexually mature 2-year-old males. Our results supported the hypothesis that entrance into NUCs with a female before she exhibits estrus was a premating tactic that increased male reproductive success when exhibited in concert with other mating tactics such as territorial defens

Integrating microclimatic variation in phenological responses to climate change: A 28-year study in a hibernating mammal

Phenological shifts associated with directional changes in climate, resulting in earlier spring activities, have been documented in several animal species. However, the extent to which species respond to overall climate change versus local climate variation is rarely studied. In addition, climate data are usually averaged over large spatial scales, even though local heterogeneity in habitats may be high, and species might be more susceptible to changes in local rather than global climate conditions. In this study, we examined the effects of spatiotemporal climate variation and climate change on the phenology of a hibernating mountain rodent, the Columbian ground squirrel (Urocitellus columbianus). Over 28 years of research (1992–2019), we studied the relationship between the microclimatic conditions experienced by adult and juvenile ground squirrels from four neighboring meadows, and their dates of emergence from hibernation. We used a microclimate model to calculate microclimate variables (local snow depth, soil temperature, air temperature, wind speed, and humidity) at an hourly scale, a 5-m spatial resolution, and at animal height on the study sites over 28 years. Emergence dates varied with age and sex, among years, as well as among and within meadows, with some areas averaging up to 10 days earlier emergence dates from hibernation than others. While emergence dates tended to be delayed throughout the study period, long-term temporal changes and interannual variability in emergence dates differed among meadows and depended on individual age and sex. Dates of hibernation emergence were correlated with local climate variables considered either during hibernation or during the preceding summer. Ground squirrels emerged earlier in years or at locations when/where snow melted earlier (years: all individuals excluding 2-year-old males, locations: yearlings and older females), and when the previous summer was less windy (≥3-year-old individuals) and more humid (2-year-old males). Two-year-old male ground squirrels also emerged later in locations where snow depth during winter was higher. Using a microclimate model allowed realistic predictions of phenological responses to climate, highlighting its potential for research on animal responses to abiotic change