Columbian Ground Squirrels Research Articles

Preparing for hibernation in ground squirrels: adrenal androgen production in summer linked to environmental severity in winter

Summary1. At high latitudes, evolutionary adaptations focus on those that maximize survival, with hibernation being a major one used by many smaller mammals. Typically, mammalian hibernators overwinter in sites that are ≈0°C. However, in arctic regions, such sites do not exist, necessitating hibernation at sites well below 0°C. Lipid, the normal fuel of most hibernators, may not provide sufficient glucose needed by certain tissues to permit survival, with muscle breakdown being required. Critical to enhancing muscle stores are high concentrations of anabolic androgens prior to hibernation when the gonads are inactive.2. We compare and contrast androgen levels in arctic ground squirrels (AGS) (Urocitellus parryii Richardson) from the Yukon and Columbian ground squirrel (CGS) (U. columbianus Ord) from southern Alberta.3. In males, changes in testes mass over the active season were similar between AGS and CGS. In contrast, during the breeding and the nonbreeding, pre‐hibernation periods, androgen levels in AGS were 6–10 and 20–25 times, respectively, those of CGS. From the breeding to the pre‐hibernation periods, androgen levels declined 41% in AGS, but 86% in CGS. In females, androgen levels in AGS were high throughout the active season and, prior to hibernation, were 24 times those in CGS.4. In pre‐hibernating AGS, we determined the source of these high androgen levels from two studies. First, using a hormonal challenge protocol to probe the hypothalamic‐pituitary‐adrenal axis, we found that androgen levels in both females and males decreased ≥10% in response to suppression by dexamethasone (an artificial glucocorticoid that inhibits ACTH release) and increased ≥18% in response to direct adrenal stimulation by adrenocorticorticotropic homone (ACTH). Second, by sequential hormonal injections in males of gonadotropin‐releasing hormone (GnRH) and of ACTH coupled with gonadectomy (GDX), followed by adrenalectomy (ADX), we found that GnRH had no effect, whereas ACTH stimulated androgen levels by >40%, both before and after GDX. After ADX, levels fell by 80%. Thus, the adrenals, not the gonads, are the source of these androgens.5. We hypothesize that pre‐hibernating AGS have evolved a solution seen in no other known mammal: exploiting the benefits of high adrenal androgen levels prior to hibernation to build muscle that is then catabolized overwinter. The unknown is how AGS have mitigated the costs of these high androgen levels.

No experimental effects of parasite load on male mating behaviour and reproductive success

Parasites can negatively affect their host’s physiology and morphology and render host individuals less attractive as mating partners. The energetic requirements of defending against parasites have to be traded off against other needs such as feeding activity, territoriality, thermoregulation or reproduction. Parasites can affect mating patterns, with females preferentially mating with parasite-resistant or parasite-free partners. We tested experimentally whether removal of both ectoparasites and endoparasites on free-living, male Columbian ground squirrels, Urocitellus columbianus, affected male mating behaviour, reproductive success and seasonal and posthibernation weight gain compared to control males. We predicted that experimental males would lose less body mass and mate more often than control males. In addition, we predicted experimental males would copulate earlier than control males in the mating sequences of receptive females and sire more offspring, because this species exhibits a strong first-male paternity advantage. Parasite treatment significantly reduced the parasite loads of experimental males. None of these males had ectoparasites at the end of the season, compared to 70% infestation of the control males. However, contrary to our expectations, the experimental treatment did not affect male reproductive behaviour (mating frequency, mating position, consort duration and mate-guarding duration), did not increase male reproductive success, and did not influence male body mass. We conclude that parasite infestation plays a minor role in affecting male reproductive behaviour, maybe because of the overall low infestation rates. Alternatively, males may be able to compensate for any costs associated with moderate loads of parasites.

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 t...

A quantitative genetic analysis of hibernation emergence date in a wild population of Columbian ground squirrels

The life history schedules of wild organisms have long attracted scientific interest, and, in light of ongoing climate change, an understanding of their genetic and environmental underpinnings is increasingly becoming of applied concern. We used a multi-generation pedigree and detailed phenotypic records, spanning 18 years, to estimate the quantitative genetic influences on the timing of hibernation emergence in a wild population of Columbian ground squirrels (Urocitellus columbianus). Emergence date was significantly heritable [h(2) = 0.22 ± 0.05 (in females) and 0.34 ± 0.14 (in males)], and there was a positive genetic correlation (r(G) = 0.76 ± 0.22) between male and female emergence dates. In adult females, the heritabilities of body mass at emergence and oestrous date were h(2) = 0.23 ± 0.09 and h(2) = 0.18 ± 0.12, respectively. The date of hibernation emergence has been hypothesized to have evolved so as to synchronize subsequent reproduction with upcoming peaks in vegetation abundance. In support of this hypothesis, although levels of phenotypic variance in emergence date were higher than oestrous date, there was a highly significant genetic correlation between the two (r(G) = 0.98 ± 0.01). Hibernation is a prominent feature in the annual cycle of many small mammals, but our understanding of its influences lags behind that for phenological traits in many other taxa. Our results provide the first insight into its quantitative genetic influences and thus help contribute to a more general understanding of its evolutionary significance.

PREPARING TO HIBERNATE IN A DEEP FREEZE: ADRENAL ANDROGEN PRODUCTION IN SUMMER LINKED TO ENVIRONMENTAL SEVERITY IN WINTER IN ARCTIC GROUND SQUIRRELS

Event Abstract Back to Event PREPARING TO HIBERNATE IN A DEEP FREEZE: ADRENAL ANDROGEN PRODUCTION IN SUMMER LINKED TO ENVIRONMENTAL SEVERITY IN WINTER IN ARCTIC GROUND SQUIRRELS Rudy Boonstra1*, Adrian Bradley1, 2 and Brendan Delehanty1 1 University of Toronto Scarborough, Biological Sciences, Canada 2 University of Queensland,, School of Biomedical Sciences, Australia At high latitudes, evolutionary adaptations for winter focus on those that maximize survival, with hibernation being a major one used by many smaller mammals. Typically, mammalian hibernators overwinter in sites that are ≥ 0 °C. In the arctic, such sites do not exist. Lipid, the normal fuel of most hibernators, may not provide sufficient glucose needed by certain tissues to permit survival, with muscle breakdown being required. Critical to enhancing muscle stores are high concentrations of anabolic androgens at a time when the gonads are inactive. We compare arctic ground squirrels (AGS) from the Arctic and Columbian ground squirrel (CGS) from Alberta. In males, changes in testes mass over the active season were similar in AGS and CGS, being at a maximum prior to breeding, declining rapidly during the breeding period and, by late summer, being <10% of that at emergence. In contrast, during the breeding and pre-hibernation periods, levels in AGS were 6-10 and 20-25 times, respectively, those of CGS. From the breeding to the pre-hibernation periods, levels declined 41% in AGS, but 86% in CGS. In female AGS, androgen levels were high throughout the active season and, prior to hibernation, were 24 times those in female CGS. Androgen levels in both female and male AGS, decreased >10% in response to dexamethasone and increased >18% in response ACTH. These results implicate the adrenals as the source of the androgens. In male AGS, GnRH had no effect on androgen levels, whereas ACTH stimulated them by > 40%, both before and after gonadectomy. Adrenalectomy caused levels to fall by 80%. Thus, the adrenals, not the testes, are the source of the AGS androgens. We conclude that pre-hibernating AGS have evolved a solution seen in no other known mammal: exploiting the benefits of high adrenal androgen levels in nonbreeding animals to build muscle that is then catabolized overwinter. The unknown is how they have mitigated the costs of these steroids. (supported by NSERC grant to RB, Univ. Queensland grant to AJB, DINA grant to BD) Keywords: adrenal steroids, anabolic steroids, arctic climate, Hibernation, muscle anabolism and catabolism, seasonal reproductive status Conference: NASCE 2011: The inaugural meeting of the North American Society for Comparative Endocrinology, Ann Arbor, United States, 13 Jul - 16 Jul, 2011. Presentation Type: Oral Presentation Topic: Environmental endocrinology Citation: Boonstra R, Bradley A and Delehanty B (2011). PREPARING TO HIBERNATE IN A DEEP FREEZE: ADRENAL ANDROGEN PRODUCTION IN SUMMER LINKED TO ENVIRONMENTAL SEVERITY IN WINTER IN ARCTIC GROUND SQUIRRELS. Front. Endocrinol. Conference Abstract: NASCE 2011: The inaugural meeting of the North American Society for Comparative Endocrinology. doi: 10.3389/conf.fendo.2011.04.00006 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 11 Jul 2011; Published Online: 09 Aug 2011. * Correspondence: Dr. Rudy Boonstra, University of Toronto Scarborough, Biological Sciences, Toronto, Ontario, M1C 1A4, Canada, boonstra@utsc.utoronto.ca Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Rudy Boonstra Adrian Bradley Brendan Delehanty Google Rudy Boonstra Adrian Bradley Brendan Delehanty Google Scholar Rudy Boonstra Adrian Bradley Brendan Delehanty PubMed Rudy Boonstra Adrian Bradley Brendan Delehanty Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Counterintuitive effects of large‐scale predator removal on a midlatitude rodent community

Historically, small mammals have been focal organisms for studying predator-prey dynamics, principally because of interest in explaining the drivers of the cyclical dynamics exhibited by northern vole, lemming, and hare populations. However, many small-mammal species occur at relatively low and fairly stable densities at temperate latitudes, and our understanding of how complex predator assemblages influence the abundance and dynamics of these species is surprisingly limited. In an intact grassland ecosystem in western Montana, USA, we examined the abundance and dynamics of Columbian ground squirrels (Spermophilus columbianus), deer mice (Peromyscus maniculatus), and montane voles (Microtus montanus) on 1-ha plots where we excluded mammalian and avian predators and ungulates, excluded ungulates alone, or allowed predators and ungulates full access. Our goal was to determine whether the relatively low population abundance and moderate population fluctuations of these rodents were due to population suppression by predators. Our predator-exclusion treatment was divided into two phases: a phase where we excluded all predators except weasels (Mustela spp.; 2002-2005), and a phase where all predators including weasels were excluded (2006-2009). Across the entire duration of the experiment, predator and/or ungulate exclusion had no effect on the abundance or overall dynamics of ground squirrels and deer mice. Ground squirrel survival (the only species abundant enough to accurately estimate survival) was also unaffected by our experimental treatments. Prior to weasel exclusion, predators also had no impacts on montane vole abundance or dynamics. However, after weasel exclusion, vole populations reached greater population peaks, and there was greater recruitment of young animals on predator-exclusion plots compared to plots open to predators during peak years. These results suggest that the impacts of predators cannot be generalized across all rodents in an assemblage. Furthermore, they suggest that specialist predators can play an important role in suppressing vole abundance even in lower-latitude vole populations that occur at relatively low densities.

Male reproductive tactics to increase paternity in the polygynandrous Columbian ground squirrel (Urocitellus columbianus)

In polyandrous and polygynandrous species where females mate with multiple partners, males are expected to maximize their fitness by exhibiting an array of reproductive behaviors to ensure fertilization success, such as competing for the best mating order within a mating sequence, optimizing their investment in copulation, and mate guarding. Though there is genetic evidence of a first-male precedence in siring success for many mammalian species, the causes of this effect are poorly understood. We studied influences on first-male precedence in Columbian ground squirrels (Urocitellus columbianus). We found that the time a male spent consorting and mate guarding declined with his mating order (both the highest for the first male to mate). Mate guarding by the first male significantly reduced, but did not exclude, the number of additional males a female accepted. Later mating males reduced the time spent consorting, suggesting a perceived decreased chance of fertilization success. Consortship and mate guarding durations were positively related to the male’s siring success and to each other, suggesting that males adjusted these behaviors strategically to increase their chances of fertilization success. Our results suggest that besides being the first male to consort, first-male sperm precedence is further enhanced through longer mating bouts and by suppressing the chances and/or efforts of later mating males.

Scent communication by female Columbian ground squirrels, Urocitellus columbianus

Scent-marking is a frequent behaviour of highly social ground squirrels and might play an important role in their social dynamics. Female Columbian ground squirrels exhibit considerable scent-marking during the reproductive period. We examined how gestating and lactating females responded to jugal gland scent-marks of same-sexed and opposite-sexed conspecifics with attention to genetic relatedness and the geographical location of the territory of individuals. We tested the dear-enemy, threat-level and kin-discrimination hypotheses to explain patterns of scent-marking. Females sniffed the scent of non-neighbouring males significantly longer than other types of scent categories and tended to over mark the scent of females more than the scent of males. Furthermore, females sniffed significantly longer at scents during gestation than during lactation. We concluded that scent-marking mainly functioned in the defence of female territories and for protection of pups against infanticidal females (threat-level hypothesis). Our results were also in accordance with the kin-discrimination hypothesis, because greater attention was paid to the marks of non-kin females. Kin females might not pose an infanticidal threat, perhaps explaining greater tolerance among related reproductive females. We concluded that scent-marking may be a relatively low-cost means of territorial defence, as well as a means of communication of aspects of individual identity.

Kinship does not affect vigilance in Columbian ground squirrels (Urocitellus columbianus)

Vigilance, a vital behaviour in prey species, is affected by many factors, including social group size and possibly the presence of relatives. Columbian ground squirrels ( Urocitellus columbianus (Ord, 1815)) show a group-size effect of reduced individual vigilance in larger groups owing to increased predator detection. Such groups are composed of both kin and nonkin individuals. We observed vigilance (raising head above shoulders while foraging) of yearling males and yearling and older females, and examined kin relationships that are learned in the natal nest (viz., uterine kin). We then tested for possible effects of kinship on vigilance and thus on the group-size effect. Because of the kin-biased behaviours and nepotistic alarm calls shown by ground squirrels in previous studies, we expected either a kin-cooperative influence on vigilance or a nepotistic asymmetrical effect on vigilance,. We found that the presence of kin (whether above ground or not) had little or no effect on vigilance. This lack of kin effect reveals that Columbian ground squirrels do not rely any more on close relatives than on unrelated group members for detecting predators. Thus, the presence of kin does not contribute to the group-size effect on vigilance.

Mating order and reproductive success in male Columbian ground squirrels (Urocitellus columbianus)

Multiple mating by females is common in many mammalian species, often resulting in mixed paternity litters. In such mating systems, mating order, male age, and male body mass frequently play an important role in determining male reproductive success. We tested for these effects on male reproductive success in Columbian ground squirrels (Urocitellus columbianus). The mating activity of estrous females was observed, and the occurrence of sperm precedence was tested using microsatellites to determine paternity in a total of 147 litters (434 offspring), including 110 litters (334 offspring) where the mating position of individual males was determined. Females mated with up to 8 males per litter, whereas paternity analyses revealed that only the first 5 males to mate actually sired offspring. The number of offspring sired significantly decreased with position in the mating sequence, showing a strong first male advantage. The extent of this advantage diminished with an increasing number of male mating partners, indicating that sperm competition plays an important role. A male’s position in the females’ mating sequences was not consistent within and across seasons, suggesting that individual males did not follow distinct reproductive strategies. Rather, males of intermediate age were more successful than young and old males, when corrected for age effects; heavier males were more likely to mate first. We conclude that males gain the largest part of their seasonal reproductive output from mating first with a female due to a pronounced first male advantage but gain considerable additional fitness from mating with additional, already mated females. Key words: Columbian ground squirrel, first male advantage, mating strategy, multiple paternity, senescence, Urocitellus columbianus. [Behav Ecol]

Kin selection in Columbian ground squirrels ( Urocitellus columbianus ): littermate kin provide individual fitness benefits

Since W. D. Hamilton's seminal work on the evolution of sociality, a large body of research has accumulated on how kin selection might explain the evolution of cooperation in many group-living species. Our study examined the evolutionary basis of philopatry and cooperation; specifically, whether individuals benefit from the presence of close kin. We applied an individual fitness approach to a 16-year study of Columbian ground squirrels (Urocitellus columbianus) to investigate potential causal paths by which the presence of kin might act on individual fitness. Our results indicate that individual fitness benefits resulted from associations of philopatric female kin, and support the hypothesis that increased tolerance of proximity of kin is a proximate mechanism for these benefits. The major life-history influence of kin on individual fitness was through improved reproductive success, and this benefit may have been owing to philopatric settlement of kin that were recognized through familiarization in the natal burrow. Thus, we demonstrated an evolutionary basis necessary for ongoing kin-selected cooperation in Columbian ground squirrels, though the mechanism of familiarity may determine which kin individuals benefit from cooperative behaviours.

Assessment of the Stress Response in Columbian Ground Squirrels: Laboratory and Field Validation of an Enzyme Immunoassay for Fecal Cortisol Metabolites

Stress responses play a critical role in the ecology and demography of wild animals, and the analysis of fecal hormone metabolites is a powerful noninvasive method to assess the role of stress. We characterized the metabolites of injected radiolabeled cortisol in the urine and feces of Columbian ground squirrels and validated an enzyme immunoassay for measuring fecal cortisol metabolites (FCM) with a 5 alpha-3beta,11 beta-diol structure by stimulation and suppression of adrenocortical activity and by evaluation of the circadian pattern of FCM excretion. In addition, we also evaluated the impact of capture, handling, and acclimation to the laboratory on FCM. Cortisol is highly metabolized, with virtually none being excreted, and of the radiolabeled cortisol injected, 31% was recovered in urine and 6.5% in feces. The lag time between cortisol injection and its appearance in urine and feces was 4.5 +/- 0.82 (SE) h and 7.0 +/- 0.53 (SE) h, respectively. FCM levels varied over the day, reflecting circadian variation in endogenous cortisol. Dexamethasone decreased FCM levels by 33%, and ACTH increased them by 255%. Trapping and housing initially increased FCM levels and decreased body mass, but these reversed within 3-7 d, indicating acclimation. Finally, FCM levels were modestly repeatable over time (r=0.57) in wild, live trapped, nonbreeding animals, indicating that FCMs provide a measure of the squirrel's stress-axis state. This assay provides a robust noninvasive assessment of the stress response of the Columbian ground squirrel and will facilitate an integration of its life history and physiology.

Maternal influences on reproduction in two populations of Columbian ground squirrels

In this study, we examined influences of maternal traits on offspring birth mass, growth rate, and weaning mass for two populations of Columbian ground squirrels (Spermophilus columbianus). We tested relationships between maternal body condition, structural size, change in mass (during gestation, during lactation, and during the entire reproductive period), timing of reproduction, and litter size on offspring traits using path analyses. To assess whether maternal investment in offspring traits extended beyond the period of direct maternal care, we examined associations between offspring traits and overwinter survival of pups. In general, females in better condition raised pups that were heavier at weaning and that had faster growth rates during lactation. Litter size had a negative effect on mass and growth rate, and only litter size had a significant effect on birth mass. For both populations, the average weaning mass of pups within a litter had a positive effect on the number of pups that survived to yearling age. In a population for which birth masses and growth rates were available, pups with faster growth rates survived better to yearling age, whereas birth mass had no effect on the number of surviving offspring in litters. We found substantial maternal influences on offspring growth and size, and evidence that these influences may extend beyond the juvenile period and constitute influences on fitness. The key to arriving at these conclusions was to take the number of offspring into account before testing for maternal effects.

Simple and integrated detours: field tests with Columbian ground squirrels

An internal representation of space offers flexibility to animals during orientation and allows execution of short cuts and detours. We tested the ability of 19 free-ranging Columbian ground squirrels (Spermophilus columbianus) to perform integrated detours that required travelling under- and aboveground. Squirrels were individually tested on their territories (2 tests) and in an arena (7 tests). During tests, animals could reach food by running aboveground and then through tunnels. For the territory tests, natural tunnels were available. For the arena tests, animals used artificial tunnels within a fenced-in part of the meadow. For the last arena test, tubes were placed aboveground replicating the underground structure. In this test animals were asked to make a simple detour, when the full path to the goal was visible. On their territories, 41% of squirrels performed detours. All animals reached the food in the arena. When choosing an arena detour, squirrels based their decision on the proximity of the burrow as well as on whether it led to food. On the last arena test, more squirrels performed correct detours on the first attempt compared to other tests. The results suggest that ground squirrels can perform simple and integrated detours, but animals perform better if the full path is visible.

Why are Male Columbian Ground Squirrels Territorial?

AbstractMale territorial defence is a component of many vertebrate mating systems and is often regarded as a tactic for acquiring mates. Traditionally considered within the context of overt site‐specific defence, territoriality actually may have several components which encompass a variety of behavioural tactics (e.g. post‐copulatory mate‐guarding, defence of resources that females need, defence of area around females) that underlie a mating system. The purpose of our study was to evaluate such influences on the territorial behaviour of male Columbian ground squirrels in southwestern Alberta, Canada. Males were dominant and territorial if they defended a minimum convex polygon activity range by chasing other males more within the activity range than they were chased. Subordinate males had no territory and were chased throughout their ranges, but they competed for mates by increasing chases in their activity range when nearby females were oestrous. Dominant males exhibited conditional breeding tactics, tending to chase other dominant males from their territory when nearby females were oestrous, but travelling outside their activity ranges to chase subordinate males when females were not oestrous. Although females mated first with a dominant male on whose territory they resided (and in order from oldest to youngest if several territories overlapped), mating pairs were not exclusive, as females usually mated with additional males. Males also guarded females after copulation and defended females directly just before oestrus, rather than defending territoryper seduring those times. Thus, males possess a repertoire of behaviours that complement site‐specific territoriality, and territory ownership serves to facilitate a first mating with females that live on the territory.

Why Do Columbian Ground Squirrels Copulate Underground?

Abstract Columbian ground squirrels (Spermophilus columbianus) usually copulate underground in a burrow. Underground copulations might be associated with 2 nonexclusive benefits: reducing probability of predation during copulation and reducing interference by conspecific males. We tested whether either of these benefits was involved in determining if the copulation site was underground or aboveground. In 2006 and 2007, we obtained detailed information on the copulatory behavior and social interactions of free-ranging individuals in southwestern Alberta, Canada. During the 3-week annual breeding period, we also recorded the activity of predators of Columbian ground squirrels such as ravens, foxes, and hawks. Squirrels that lived on the periphery of the population were more susceptible to predation than squirrels in the center. Despite this risk, aboveground copulations usually occurred on peripheral territories. In addition, aboveground copulations were not further removed in time from predator attacks or ...

Why do female Columbian ground squirrels (Spermophilus columbianus) give an estrus call?

Female Columbian ground squirrels ( Spermophilus columbianus (Ord, 1815)) sometimes emit a repetitive vocalization after copulation. We examined two possible explanations for why sexual selection would favor expression of these “estrus calls”: to encourage sperm competition through mating with additional males and to increase mate guarding by the consort male as a mechanism of postcopulatory female mate choice. During three annual mating periods, we observed mating behaviour, estrus calls, and postcopulatory behavioural interactions of free-ranging individuals. Predictions of the advertisement hypothesis were supported, as females typically solicited courtship interactions with nonconsort males directly after emitting an estrus call. Thus, females that emitted an estrus call were more likely to acquire additional matings than noncalling females, particularly if calls were emitted after the female’s first mating. These results were not consistent with predictions of the postcopulatory female mate choice hypothesis, as calling females should initiate social contact with the consort male and stay proximate to the copulatory site after copulation if they are encouraging mate guarding. For reasons that remain unclear, the probability that an estrus call would follow mating increased linearly with the age of the consort male. However, our results taken together suggest that estrus advertisement is the most likely social context of female postcopulatory calling.

Previous Experience and Reproductive Investment of Female Columbian Ground Squirrels

Reproductive success of females in iteroparous species usually increases early in life, then remains constant or declines. The restraint hypothesis suggests that primiparous females limit their 1st reproduction in order to avoid future costs to survival, reproduction, or both, whereas constraint indicates that primiparous females are limited in their 1st reproductive attempt either because they lack sufficient resources (measured by body mass) or lack experience at weaning a litter. To evaluate these alternatives, we examined age- and experience-related patterns of reproduction in female Columbian ground squirrels (Spermophilus columbianus) with data from a long-term study and by experimentally altering age at 1st reproduction. In the results of the long-term study, experienced females had significantly higher reproductive investment and reproductive success (number of offspring surviving to yearling age) compared to inexperienced females. Annual survival of females was not affected by their level of previous weaning experience or current reproductive investment. Additionally, subsequent reproductive success was not impaired by earlier reproduction. In the experimental results, experienced females had significantly higher reproductive investments compared to inexperienced females. Constraint in terms of previous weaning experience best explained the differences in reproductive investment and reproductive success between primiparous and multiparous females.

Social networking in the Columbian ground squirrel, Spermophilus columbianus

Networks are collections of units that potentially interact as a system. Electronic power grids, human societies, the Internet, food webs and metabolic pathways are examples of networks that have emergent properties that allow all vertices (viz. individuals, components, species, etc.) to be linked by a short chain of intermediate vertices. My field observations on a colony of 65 free-ranging Columbian ground squirrels suggest that their society also exhibits these characteristics via social interaction. On average, any dyad of squirrels in the colony can be connected via amicable interaction with three intermediate individuals. The connectivity of individuals (viz. the number of individuals to which an individual is directly connected) decays following a scale-free power law distribution. Individuals that have similar age, reproductive status and number of associates (viz. the number of individuals to which the individual is connected via social interaction) interact amicably with each other more than other squirrels. The network is robust to the removal of random individuals. However, simulated removal of individuals that are connected to many other squirrels increases the number of intermediates between two random individuals and fragments the network into smaller clusters when removals exceed 10% of the individuals in the colony. Thus, certain individuals appear to play more central roles than others in the cohesion of the network. My results reinforce previous studies showing that network theory can be used to determine the roles played by individuals in the cohesion of animal societies, thus providing a framework for studying sociality across species.

Ecology and Translocation‐Aided Recovery of an Endangered Badger Population

Abstract Southern British Columbia, Canada, is the northwestern range limit of the American badger (Taxidea taxus) and supports a nationally endangered subspecies. We initially investigated space‐use, diet, and demography in southeastern British Columbia to characterize range‐limit ecology. Resident badgers in the northern part (NP) of our study area were extirpated or nearly so during our study (λ = 0.7), whereas the southern (SP) badger population remained viable (λ = 1.2). This apparent difference in viability between NP and SP may have been confounded by timing because research occurred later in SP; litter size, number of Columbian ground squirrels (Spermophilus columbianus) consumed, and home range size were each correlated nearly equally to latitude and date of research, and survivorship was greater later in the study for both the NP and SP. Collectively, these factors indicated temporal, not just spatial, variability. Therefore, we translocated badgers into the NP to 1) determine whether the NP had lost its capacity to support badgers or had merely experienced the variability expected at a range limit and, if the latter, 2) initiate recovery. Translocated animals and their offspring had kit production equivalent to that of SP residents, adult survivorship intermediate between the NP and SP residents, and no confirmed kit mortality, with population growth projected (λ = 1.3). Diet of translocated individuals was similar to that of residents. Home ranges of translocated females were intermediate between the 2 resident groups, and home ranges of translocated males were not different than either resident group. Juvenile dispersal dates and distances were similar to those of residents for each sex. Our results were consistent with the extirpation of the NP being driven by temporally variable conditions or the effect of random events expected at range limits. The extirpation of NP did not appear to have been primarily due to any permanent loss of the NP's capacity to support badgers. At 3.5 years after starting translocations, badgers remained in the NP within an apparently growing population. We found translocation to be a useful diagnostic and conservation tool for badgers at their northern limit. Its utility may extend to countering the fluctuations typical of other rare, range‐limit species.