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Estimates of demographic parameters based on capture-mark-recapture (CMR) methods may be biased when some individuals in the population are temporarily unavailable for capture (temporary emigration). We estimated snowshoe hare abundance, apparent survival, and probability of temporary emigration in a population of snowshoe hares (Lepus americanus Erxleben, 1777) in the Yukon (Canada) using Pollock's robust design CMR model, and population density using spatially explicit CMR models. Survival rates strongly varied among cyclic phases, seasons, and across five population cycles. We found strong evidence that temporary emigration was Markovian (i.e., nonrandom), suggesting that it varied among individuals that were temporary emigrant in the previous sampling period and those that were present in the sampled area. The probability of temporary emigration for individuals that were in the study area during the previous sampling occasion ([gamma]') varied among cycles. Probability that individuals that were temporarily absent from the sampled area would remain temporary emigrants ([gamma]') showed strongly seasonal pattern, low in winter and high during summers. Snowshoe hare population density ranged from 0.017 (0.015-0.05) hares/ha to 4.43 (3.90-5.00) hares/ha and showed large-scale cyclical fluctuations. Autocorrelation functions and autoregressive analyses revealed that our study population exhibited statistically significant cyclic fluctuations, with a periodicity of 9-10 years. Key words: autoregressive analysis, boreal ecosystem, capture-mark-recapture analysis, capture probability, Lepus americanus, density dependence, Pollock's robust design, snowshoe hare cycles, survival, spatial capture-recapture model, temporary emigration, wildlife's 10-year cycle. Les estimations de parametres demographiques reposant sur des methodes de capture-marquage-recapture (CMR) pourraient etre biaisees dans les situations ou certains individus de la population sont provisoirement non disponibles pour la capture (emigration temporaire). Nous avons estime l'abondance, le taux de survie apparent et la probabilite d'emigration temporaire au sein d'une population de lievres d'Amerique (Lepus americanus Erxleben, 1777) au Yukon (Canada) en utilisant le modele CMR a schema robuste de Pollock, et la densite de la population en utilisant des modeles CMR spatialement explicites. Les taux de survie variaient considerablement au fil des phases du cycle et des saisons et entre cinq cycles demographiques. Nous avons releve des indices solides du caractere markovien (c.-a-d., non aleatoire) de l'emigration temporaire, donnant a penser que cette derniere differe entre les individus qui etaient des emigrants temporaires durant la periode d'echantillonnage precedente et ceux qui etaient presents dans le secteur echantillonne. La probabilite d'emigration temporaire pour les individus qui etaient dans le secteur d'etude durant l'occasion d'echantillonnage precedent ([gamma]') variait entre les cycles. La probabilite que des individus qui etaient temporairement absents du secteur echantillonne demeurent des emigrants temporaires ([gamma]') presentait une forte saisonnalite, etant faible en hiver et elevee durant les etes. La densite de la population de lievres d'Amerique allait de 0,017 (0,015-0,05) lievres/ha a 4,43 (3,90-5,00) lievres/ha et presentait de vastes fluctuations cycliques. Des fonctions d'autocorrelation et des analyses autoregressives ont revele que la population etudiee presentait des fluctuations cycliques statistiquement significatives, d'une periodicite de 9-10 ans. [Traduit par la Redaction] Mots-cles : analyse autoregressive, ecosysteme boreal, analyse de capture-marquage-recapture, probabilite de capture, Lepus americanus, dependance sur la densite, schema robuste de Pollock, cycles des lievres d'Amerique, survie, modele spatial de capture-recapture, emigration temporaire, cycle demographique decennal., Introduction Studies of population dynamics often rely on individual-based data collected by following fates of individuals that are uniquely marked. When such data are available, capture-mark-recapture (CMR) methodologies offer a [...]

Phenotypic differences often stem from genetic/maternal differences and/or early-life adaptations to local environmental conditions. In colonial animals, little is known on how variation in the social environment is embedded into individual phenotypes, nor what the consequences are on individual fitness. We conducted an experimental cross-fostering study on king penguins (Aptenodytes patagonicus), exchanging eggs among 134 pairs breeding in high-density (67 pairs) or low-density (67 pairs) areas of the same breeding colony. We investigated differences in parent and chick phenotypes and survival in relation to the density of their origin and foster environment. Adults breeding in colony areas of high density exhibited decreased resting behaviour and increased aggression and vigilance, increased hypometabolism during incubation fasts, and more moderate corticosterone responses shaped by exposure to chronic stressors (e.g. constant aggression by neighbours). Chick phenotypes were more influenced by the environment in which they were raised than their genetic/maternal origin. Chicks raised in high-density colonial environments showed enhanced weight gain and survival rates regardless of the density of their genetic parents' breeding areas. Our study experimentally shows advantages to breeding in colonial areas of higher breeder densities in king penguins, and highlights the importance of social settings in shaping phenotype expression in colonial seabirds. [ABSTRACT FROM AUTHOR]

The relationship between body size and latitude has been the focus ofdozensof studies across many species. However, results of testing Bergmann's rule--that organisms in colder climates or at higher latitudes possess larger body sizes--have been inconsistent across studies. We investigated whether snowshoe hares (Lepus americanus Erxleben, 1777) follow Bergmann's rule by investigating differences in body mass using data from six published studies and from data of 755 individual hares captured from 10 populations across North America covering 26[degrees] of north latitude. We also explored alternative hypotheses related to variation in hare body mass, including winter severity, length of growing season, elevation, and snow depth. We found body mass of hares varied throughout their range, but the drivers of body mass differed based on geographic location. In northern populations, females followed Bergmann's rule, whereas males did not. In northern populations, male mass was related to mean snow depth. In contrast, in southern populations, body mass of both sexes was related to length of the growing season. These differences likely represent variation in the drivers of selection. Specifically, in the north, a large body size is beneficial to conserve heat because of low winter temperatures, whereas in the south, it is likely due to increased food supply associated with longer growing seasons. Key words: snowshoe hare, Lepus americanus, latitudinal variation, energy expenditure, food supply, winter, snow depth, growing season. Le lien entre la taille du corps et la latitude a fait l'objet de dizaines d'etudes portant sur de nombreuses especes. Les resultats des etudes visant a valider la regle de Bergmann, qui stipule que les organismes vivant en climat plus froid ou a plus haute altitude auraient des corps de plus grandes tailles, ne sont pas coherents d'une etude a l'autre. Nous avons verifie si les lievres d'Amerique (Lepus americanus Erxleben, 1777) suivaient la regle de Bergmann en examinant les differences de masse corporelle dans des donnees de six etudes publiees et pour 755 lievres captures de 10 populations reparties a la grandeur de l'Amerique du Nord, sur un territoire couvrant 26[degrees] de latitude nord. Nous avons aussi examine differentes hypotheses concernant les variations de la masse corporelle de lievres, touchant notamment a la rigueur de l'hiver, la duree de la periode vegetative, l'altitude et l'epaisseur de la neige. Nous avons constate que la masse corporelle des lievres varie dans toute leur aire de repartition, mais que les facteurs qui l'influencent different selon l'endroit. Dans les populations nordiques, les femelles suivent la regle de Bergmann, mais non les males. Dans les populations nordiques, la masse des males est reliee a l'epaisseur moyenne de la neige, alors que dans les populations meridionales, la masse corporelle des deux sexes est reliee a la duree de la periode vegetative. Ces differences representent vraisemblablement des variations des facteurs influant sur la selection. Plus precisement, au nord, une grande taille du corps est utile parce qu'elle facilite la conservation de chaleur pour faire face aux faibles temperatures hivernales, alors que dans le sud, elle est probablement due a un meilleur approvisionnement en nourriture associe a des periodes vegetatives plus longues. [Traduit par la Redaction] Mots-cles : lievre d'Amerique, Lepus americanus, variation latitudinale, depense energetique, approvisionnement en nourriture, hiver, epaisseur de la neige, periode vegetative., Introduction Latitudinal variation in body size is a phenomenon common across many taxa (McNab 1971; Ashton etal. 2000; Meiri and Dayan 2003). In particular, Bergmann's rule states that, within a [...]

Groundberries are an important component of the flora of the boreal forest and provide seasonally important food for many birds and mammals, as well as local people in northern Canada. Here, we ask whether there has been a change in the cover of groundberries in the Yukon boreal forest over the last two decades. We monitored five common species at undisturbed forest sites spaced 300 km apart. At our Kluane site, we monitored 710 fixed quadrats per year for 26 years (1997–2022), and at Mayo 500 quadrats per year for 18 years (2005–2022). The cover of four species, Arctostaphylos uva-ursi (L.) Spreng. (bearberry), Arctostaphylos rubra (Rehder & E.H. Wilson) Fernald (red bearberry), Empetrum nigrum L. (crowberry), and Geocaulon lividum (Richardson) Fernald (toadflax), declined annually by 0.2%–0.8% at both sites. In contrast, Vaccinium vitis-idaea L. (lingonberry) increased annually by 0.5% and 0.8%. We tested whether increases in summer temperature and rainfall were correlated with the observed changes but found no significant relationships. These boreal plants are changing in abundance, but we have limited data on the extent and speed of these changes. We recommend experiments to understand the cause(s) of these changes in groundberry productivity. Our study is a start in monitoring important berry species in this critical ecosystem of northern Canada. [ABSTRACT FROM AUTHOR]

Perceived predation risk alters prey behaviour and physiology, but few studies have examined downstream consequences on prey demography in wild populations. Perceived predation risk could alter adult reproductive performance via reduced investment in offspring quality and post-birth care. We manipulated perceived predation risk in snowshoe hare (Lepus americanus Erxleben, 1777) by exposing pregnant mothers to chases by a domestic dog (Canis familiaris Linnaeus, 1758). Litter size was comparable between risk-augmented and control groups, but treated females had more stillbirths and gave birth to leverets of lower body condition. Leverets from risk-augmented females had 88% higher 40-day mortality rate. Maternally preventable causes of death like starvation or predation by red squirrel (Tamiasciurus hudsonicus (Erxleben, 1777)) caused this difference, particularly during the nursing period. Risk-augmented mothers were always more active than controls, but the difference was greatest during the nursing period. We found that perceived predation risk reduces maternal productivity pre- and post-partum, implying downstream consequences to populations. Because our treatment ended before parturition, we can link offspring performance such as survival and behaviour specifically to maternal life-history trade-offs, which has not been shown in a wild mammal. [ABSTRACT FROM AUTHOR]

Baseline studies of small rodent populations in undisturbed ecosystems are rare. We report here 50 years of monitoring and experimentation in Yukon of a dominant rodent species in the North American boreal forest, the red‐backed vole Clethrionomys rutilus. These voles breed in summer, weigh 20–25 g, and reach a maximum density of 20 to 25 per ha. Their populations have shown consistent 3–4‐year cycles for the last 50 years with the only change being that peak densities averaged 8/ha until 2000 and 18/ha since that year. During the last 25 years, we have measured food resources, predator numbers, and winter weather, and for 1‐year social interactions, to estimate their contribution to changes in the rate of summer increase and the rate of overwinter decline. All these potential limiting factors could contribute to changes in density, and we measured their relative contributions statistically with multiple regressions. The rate of winter decline in density was related to both food supply and winter severity. The rate of summer increase was related to summer berry crops and white spruce cone production. No measure of predator numbers was related to winter or summer changes in vole abundance. There was a large signal of climate change effects in these populations. There is no density dependence in summer population growth and only a weak one in winter population declines. None of our results provide a clear understanding of what generates 3–4‐year cycles in these voles, and the major missing piece may be an understanding of social interactions at high density. [ABSTRACT FROM AUTHOR]

Corticosteroid-binding globulin (CBG) helps to regulate tissue bioavailability of circulating glucocorticoids (GCs), and in most vertebrates, [greater than or equal to]80%-90% of GCs bind to this protein. New World flying squirrels have higher plasma total cortisol levels (the primary corticosteroid in sciurids) than most vertebrates. Recent research suggests that flying squirrels have either low amounts of CBG or CBG molecules that have a low binding affinity for cortisol, as this taxon appears to exhibit very low proportions of cortisol bound to CBG. To test whether CBG levels have been adjusted over evolutionary time, we assessed the levels of this protein in the plasma of northern (Glaucomys sabrinus (Shaw, 1801)) and southern (Glaucomys volans (Linnaeus, 1758)) flying squirrels using immunoblotting, and compared the relative levels among three phylogenetically related species of sciurids. We also compared the pattern of CBG levels with cortisol levels for the same individuals. Flying squirrels had higher cortisol levels than the other species, but similar levels of CBG to their closest relatives (tree squirrels). We conclude that CBG levels in flying squirrels have not been adjusted over evolutionary time, and thus, the uncoupling of CBG levels from cortisol concentrations may represent an evolutionary modification in the lineage leading to New World flying squirrels. Key words: Glaucomys sabrinus, Glaucomys volans, glucocorticoids, northern flying squirrel, physiological ecology, Sciuridae, southern flying squirrel, Western blot. La globuline fixant les corticostéroïdes (CBG) aide à réguler la biodisponibilité pour les tissus des glucocorticoïdes (GC) en circulation, et chez la plupart des vertébrés, [greater than or equal to]80%-90% des GC se fixent à cette protéine. Les polatouches du Nouveau Monde ont des concentrations plasmatiques de cortisol total (le principal corticostéroïde chez les sciuridés) plus élevées que la plupart des vertébrés. Des travaux récents semblent indiquer que les polatouches présentent soit de faibles quantités de CBG ou des molécules de CBG ayant une faible affinité de fixation au cortisol, puisque ce taxon semble présenter de très faibles proportions de cortisol fixé à la CBG. Pour vérifier si les concentrations de CBG se sont ajustées au fil de l'évolution, nous avons évalué les concentrations de cette protéine dans le plasma de grands polatouches (Glaucomys sabrinus (Shaw, 1801)) et de petits polatouches (Glaucomys volans (Linnaeus, 1758)) par la méthode de transfert, et comparé les concentrations relatives à celles de trois espèces de sciuridés apparentées du point de vue phylogénétique. Nous avons également comparé les variations des concentrations de CBG en fonction des concentrations de cortisol pour les mêmes individus. Les polatouches présentaient des concentrations de cortisol plus élevées que les autres espèces, mais des concentrations de CBG semblables à celles de leurs parents les plus proches (écureuils arboricoles). Nous concluons que les concentrations de CBG chez les polatouches n'ont pas été ajustées au fil de l'évolution et, donc, que le découplage des concentrations de CBG des concentrations de cortisol pourrait représenter une modification adaptative dans la lignée qui a mené aux écureuils du Nouveau Monde. [Traduit par la Rédaction] Mots-clés : Glaucomys sabrinus, Glaucomys volans, glucocorticoïdes, grand polatouche, écologie physiologique, sciuridés, petit polatouche, transfert Western., Introduction The stress axis (or the hypothalamic-pituitary-adrenal (HPA) axis) allows vertebrates to survive and reproduce by providing a physiological mechanism through which they can react to stres-sors in their environment. [...]