In Vitro Digestibilities of Summer Forages Utilized by the Rivière George Caribou Herd

The Riviere George caribou herd (northern Quebec-Labrador, Canada) is thought to be regulated by forage limitations in its summer range. In such a situation, digestibilities of plants may strongly affect the diet choice and physical condition of animals. In vitro dry matter disappearance (IVDMD) of the most important summer forages of the Riviere George caribou herd was determined during fermentation periods of 12, 24, and 48 h using rumen fluid collected from a Holstein cow. IVDMD values for Cyperaceae (Eriophorum angustifolium and Carex rariflora), and shrubs (Betula glandulosa and Vaccinium uliginosum) collected in July and August were higher for long fermentation periods (48 h) than for shorter ones (12 and 24 h). Plants collected in early summer were also more digestible than those collected in late summer. Contrary to my prediction, both Cyperaceae were more digestible than the two shrubs in mid-July. However, no difference occurred in early August. The fermentation period did not affect the IVDMD of lichens; maximum digestibility was attained after 12 h. Alectoria ochroleuca and Cetraria spp. were more digestible than Cladina rangiferina, Cladina stellaris, and Stereocaulon paschale, likely because of their lower fibre content. These results suggest that the preference of caribou for Cladina spp. is not based on digestibility, but probably on the fact that these species are abundant in the Riviere George area. Variations in IVDMD seem to be explained by plant phenology, because longer fermentation periods were necessary to attain a high level of digestibility as summer progressed. Plant digestibility alone cannot explain caribou summer diet. Other variables such as plant constituents (e.g. protein) and relative abundance must also be considered.Il a été suggéré que l'abondance du troupeau de caribous de la rivière George (Québec nordique-Labrador, au Canada) était régulée par la disponibilité de nourriture dans les habitats d'été. Dans un tel système, la digestibilité des plantes peut affecter de façon importante le régime alimentaire et la condition physique des animaux. La disparition in vitro de la matière sèche (DIVMS) des principales espèces végétales composant la nourriture estivale des caribous de la rivière George a été déterminée durant des périodes de fermentation de 12, 24 et 48 heures, à l'aide de jus de rumen provenant d'une vache Holstein. Les valeurs de DIVMS des cypéracées (Eriophorum angustifolium et Carex rariflora) et des arbustes (Betula glandulosa et Vaccinium uliginosum) récoltés en juillet et août étaient plus élevées pour de longues périodes de fermentation (48 heures) que pour de courtes périodes (12 et 24 heures). Les plantes récoltées tôt durant l'été étaient aussi plus digestes que celles récoltées tard. Contrairement aux prédictions, les deux espèces de cypéracées étaient plus digestes que les deux espèces d'arbustes à la mi-juillet, mais pas au début août. La durée de fermentation n'a pas affecté la DIVMS des lichens, le maximum de digestibilité étant atteint après 12 heures. Alectoria ochroleuca et Cetraria spp. étaient plus digestes que Cladina rangiferina, Cladina stellaris et Stereocaulon paschale, probablement parce que leur contenu en fibres était plus faible. Ces résultats suggèrent que la préférence des caribous pour les espèces de Cladina n'est pas basée sur leur digestibilité mais probablement sur le fait que ces espèces sont abondantes dans la région de la rivière George. Les variations de DIVMS observées semblent s'expliquer par la phénologie de la végétation, des temps de fermentation plus longs étant nécessaires pour atteindre une digestibilité élevée vers la fin de l'été. La digestibilité des plantes seule ne peut donc expliquer le régime alimentaire du caribou, et d'autres variables comme la composition des plantes (e.g., le contenu en protéines) et leur disponibilité doivent aussi être considérées

Linking alternative food sources to winter habitat selection of herbivores in overbrowsed landscapes

During winter, ungulates in boreal forests must cope with high energetic costs related to locomotion in deep snow and reduced forage abundance and quality. At high density, ungulates face additional constraints, because heavy browsing reduces availability of woody browse, the main source of forage during winter. Under these severe conditions, large herbivores might forage on alternative food sources likely independent of browsing pressure, such as litterfall or windblown trees. We investigated the influence of alternative food sources on winter habitat selection, by studying female white-tailed deer (Odocoileus virginianus) living in 2 landscapes with contrasted browse abundance, recently logged and regenerated landscapes, in a population at high density and on a large island free of predators. We fitted 21 female whitetailed deer with Global Positioning System (GPS) collars and delineated winter home ranges and core areas. We measured snow conditions in different habitat categories and sampled vegetation in the core areas and in the rest of the home ranges to determine how forage abundance, protective cover, and snow conditions influenced habitat selection within the home range. In both landscapes, deer were less likely to use open habitat categories as snow accumulated on the ground. At a finer scale, deer inhabiting the regenerated landscape intensively used areas where balsam fir cover was intermediate with greater balsam fir browse density than in the rest of the home range. In the recently logged landscape, deer were more likely to be found near edges between clear-cuts and balsam fir stands and in areas where windblown balsam fir trees were present; the latter being the most influential variable. Although balsam fir browse was sparse and mainly out of reach in this landscape, deer increased the use of areas where it was present. Our results offer novel insights into the resource selection processes of northern ungulates, as we showed that access to winter forage, such as woody browse and alternative food sources, depends on climatic conditions and stochastic events, such as abundant compacted snow or windthrows. To compensate for these scarce and unpredictable food supplies, deer selected habitat categories, but mostly areas within those habitat categories, where the likelihood of finding browse, litterfall, and windblown trees was greates

Maternal defensive behavior of mountain goats against predation by golden eagles

Maternal defensive behavior against predators may appear risky but is common in many species. Herein we describe maternal defensive behavior of mountain goats (Oreamnos americanus) against Golden Eagle (Aquila chrysaetos) predatory attempts. We found that Golden Eagles attacked goats in 1.9% of sightings (n = 311 sightings of active Golden Eagles over 12 years) but were never successful. Mothers always defended their young against Golden Eagle attacks. Predation by Golden Eagles on young-of-the-year appears low for most ungulate species, including mountain goats. The benefits of defending offspring against eagles are likely high in ungulates, and we would therefore expect selection to favor maternal defensive behavior

Dominance sociale et traits d'histoire de vie chez les femelles de la chèvre de montagne

Le but principal de ce projet de recherche était d'étudier comment la dominance et les caractéristiques maternelles affectaient l'organisation sociale et les stratégies de reproduction individuelles chez un ongulé, la chèvre de montagne (Oreamnos americanus). Le suivi à long terme des comportements agressifs et de la reproduction de chèvres marquées a permis de tester des hypothèses mettant en relation les caractéristiques maternelles et la valeur sélective individuelle. L'analyse de près de 2800 interactions agressives a montré que les femelles établissaient une hiérarchie de dominance fortement linéaire qui demeurait stable au cours des années. Dans la population de Caw Ridge, l'âge de la femelle était le principal déterminant du rang social. Ces résultats suggèrent que les relations de dominance pour chaque dyade étaient établies tôt dans la vie, lorsque des différences importantes en faille corporelle entre les juvéniles et les adultes étaient encore évidentes. Un objectif important de ce projet de recherche était de déterminer les effets de la dominance sociale sur le succès reproducteur individuel des femelles. La probabilité de produire un chevreau augmentait avec l'âge de la femelle et son rang social. Les femelles qui étaient les plus dominantes pour leur âge avaient un meilleur succès reproducteur, particulièrement les jeunes femelles de 3 à 5 ans. L'âge et le rang social des femelles n'affectaient pas la survie des jeunes jusqu'au sevrage ou jusqu'à l'âge d'un an. Les conditions environnementales durant l'année de naissance peuvent aussi influencer la croissance et la survie des jeunes. La masse des chevreaux était positivement corrélée avec la qualité de la végétation au début de la période de lactation. Enfin, la dernière partie de ce travail a permis de déterminer si la qualité phénotypique d'un individu pouvait être révélée par la croissance et la symétrie au niveau de la taille des cornes, un caractère morphologique impliqué dans les comportements agressifs. Approximativement 93% de la croissance totale des cornes était complétée à l'âge de trois ans, indiquant qu'il n'y aurait pas de pression de sélection directionnelle pour des cornes plus longues après cet âge."--Résumé abrégé par UM

Simulated drilling noise affects the space use of a large terrestrial mammal

Wildlife is exposed to increasing anthropogenic disturbances related to shale oil and gas extraction in response to rising worldwide demands. As these disturbances increase in intensity and occurrence across the landscape, understanding their impacts is essential for management. On Anticosti Island (Québec, Canada), we equipped six white-tailed deer Odocoileus virginianus with GPS collars taking hourly locations. We then designed a playback experiment by simulating constant drilling noise emitted by generators to which half of the collared deer were exposed for a three-week period. Deer tolerated noise levels up to 70 dB(C). However, the number of locations recorded in areas where the noise was above 70 dB(C) was on average 73% (SE¿18%) lower than before the disturbance, which suggests that deer experienced fine scale functional habitat loss. This loss of habitat occurred up to 200 m from the noise source. The size of home ranges and movement rates did not appear to be affected by the noise disturbance. In addition, during the experiment, deer were able to relocate in areas of their home range where food availability was similar to that of sites used before the disturbance. These results show that drilling noise can affect the habitat use of white-tailed deer. However, future research is needed to better understand the cumulative impacts of shale mining on large mammals, as this study isolated only one of the many disturbances present near mining sites and for a limited perio

Deer browsing and soil disturbance induce cascading effects on plant communities : a multilevel path analysis

Understanding how large herbivores shape plant diversity patterns is an important challenge in community ecology, especially because many ungulate populations in the northern hemisphere have recently expanded. Because species within plant communities can exhibit strong interactions (e.g., competition, facilitation), selective foraging by large herbivores is likely not only to affect the abundance of palatable species, but also to induce cascading effects across entire plant communities. To investigate these possibilities, we first tested the effects of deer browsing and soil disturbance on herbaceous plant diversity patterns in boreal forest, using standard analyses of variance. Second, we evaluated direct and indirect effects of deer browsing and soil disturbance on the small-scale richness of herbaceous taxa using a multilevel path analysis approach. The first set of analyses showed that deer browsing and soil disturbance influenced herb richness. Path analyses revealed that deer browsing and soil disturbance influenced richness via complex chains of interactions, involving dominant (i.e., the most abundant) browsing-tolerant (DBT) taxa and white birch (Betula papyrifera), a species highly preferred by white-tailed deer (Odocoileus virginianus). We found no evidence that an increase of white birch in fenced quadrats was the direct cause of a decrease in herb richness. However, we found strong evidence that a higher abundance of DBT taxa (i.e., graminoids and Circium arvense), both in fenced and unfenced quadrats, increased herb layer richness. We propose an empirical model in which competitive interactions between white birch and DBT taxa regulate the strength of facilitative relationships between the abundance of DBT taxa and herb richness. In this model, deer browsing and the intensity of soil disturbance initiate a complex chain of cascading effects in boreal plant communities by controlling the abundance of white birch

Spatial extent of neighboring plants influences the strength of associational effects on mammal herbivory

There is high variability in the level of herbivory between individual plants from the same species with potential effects on population dynamics, community composition, and ecosystem structure and function. This variability can be partly explained by associational effects (i.e., the impact of the presence of neighboring plants on the level of herbivory experienced by a focal plant) but it is still unclear how the spatial scale of plant neighborhood modulates foraging choice of herbivores, an inherently spatial process in itself. Using a meta-analysis, we investigated how spatial scale modifies associational effects on the susceptibility to browsing by herbivores with movement capacities similar to deer. From 2496 articles found in literature databases, we selected 46 studies providing a total of 168 differences of means in damage by herbivores or survival to woody plants (mostly) with and without neighboring plants. Spatial scales were reported as distance between plants or as plot size. We estimated the relationships between the effect sizes and spatial scale, type of associational effects, and nature of the experiment using meta-analysis mixed models. The strength of associational effects declined with increasing plot size, regardless of the type of associational effects. Associational defenses (i.e., decrease in herbivory for focal plants associated with unpalatable neighbors) had stronger magnitude than associational susceptibilities. The high remaining heterogeneity among studies suggests that untested factors modulate associational effects, such as nutritional quality of focal and neighboring plants, density of herbivores, timing of browsing, etc. Associational effects are already considered in multiple restoration contexts worldwide, but a better understanding of these relationships could improve their use in conservation, restoration, and forest exploitation when browsing is a concern. This study is the first to investigate spatial patterns of associational effects across species and ecosystems, an issue that is essential to determine differential herbivory damages among plants

The ecology of 3-d space use in a sexually dimorphic mammal

The distribution of animals is the result of habitat selection according to sex, reproductive status and resource availability. Little is known about how marine predators investigate their 3-dimensional space along both the horizontal and vertical axes and how temporal variation affects space use. In this study, we assessed the spatio-temporal movement of a sexually dimorphic marine mammal, the grey seal Halichoerus grypus by 1) determining seasonal home range size, 2) testing whether space use of seals was affected by water depth, and 3) investigating the vertical movement of seals according to the maximum depth of each dive. Between 1993 and 2005, we fitted 49 grey seals in the Gulf of St. Lawrence with satellite transmitters. We estimated seasonal 95% fixed-kernel home ranges for each individual. For each seal, we tested for selectivity and preference for 4 water depth classes at the home range scale and within the home range. We also evaluated the proportional number of dives made in each water depth classes according to the maximum depth of each dive. Home ranges were 10 times larger in winter than in summer. Seals generally selected habitats <50 m deep. They also mainly dove to depths of 40 m or less. At both scales of selection, preference for shallow areas decreased in winter. We also observed that adults used shallow habitats more than juveniles to establish their home range. A spatial segregation based on sex also occurred at the finer scale of selection where females were more concentrated in the shallowest parts of their home range than males. Segregation in space use according to age and sex classes occurred at both the horizontal and vertical scales. Our results emphasise the importance of studying habitat selection of marine predators in 3-dimensional space, in addition to the temporal scale

Untangling effects of human disturbance and natural factors on mortality risk of migratory caribou

Human disturbances are rapidly increasing in northern and Arctic regions, raising concerns about the recovery and persistence of declining caribou (Rangifer tarandus) populations. Yet, the consequences of behavioral responses toward human disturbances on vital rates rarely have been investigated. Herein, we assessed the cumulative and instantaneous effects of human disturbances (roads, human settlements, mines and mining exploration) at different temporal scales on the mortality risk of 254 GPS- collared migratory caribou monitored in two herds, the Rivière-aux-Feuilles (RFH) and Rivière-George (RGH) herds, in northern Québec and Labrador, Canada. We also assessed the relative importance of human disturbances on caribou mortality risk compared with non-anthropogenic factors, including habitat use by caribou, predation risk by gray wolves (Canis lupus), and local weather conditions. Human disturbances alone, exclusive of hunting, had a limited impact on mortality risk of caribou. Repeated exposure to disturbances did not have detectable effects on mortality risk during the early life period (1−7 years old), but more abundant precipitation (RFH) or the use of areas with a higher predation risk (RGH) did so. At the seasonal scale, non-anthropogenic factors, particularly the use of highly selected habitat by caribou and air temperature, had a greater effect than anthropogenic factors on the mortality risk in the RFH. Caribou of the RFH using more frequently higlhy selected habitats decreased their chance of mortality during winter, whereas individuals using warmer areas during summer faced a higher risk of mortality. At the daily scale, we observed that anthropogenic and non-anthropogenic factors generally had either no effect on the daily risk of mortality, or their effects were undistinguishable from the effect of latitude, with which they were highly correlated. The only exception was for the RFH in winter, for which the daily risk of mortality increased 10 folds for each 10-km increment closer to industrial disturbances. Although the impacts of human disturbances on caribou survival were limited to specific regions and areas, we nevertheless detected a negative effect on survival on the RFH, even at the currently low level of human development. Our study highlights the importance of assessing effects of human disturbances at various spatiotemporal scales, and of considering the relative influence of other non-anthropogenic factors to fully understand drives of wildlife populations

Nitrogen allocation to offspring and milk production in a capital breeder

Nitrogen (N) is a limiting nutrient for many herbivores, especially when plant availability and N content are low during the period of maternal investment, which is common for arctic ungulates. We used natural abundance of N isotopes to quantify allocation of maternal nitrogen to neonatal calves and milk in wild migratory caribou (Rangifer tarandus). We contrasted female-calf pairs from two herds in northern Quebec/Labrador, Canada: Rivière-George herd (RG; low population size with heavy calves) and the Rivière-aux-Feuilles herd (RAF; high population size and small calves). We assessed whether females of both herds relied on body protein or dietary N to produce the neonatal calf and milk at calving and weaning. Female caribou of both herds relied mostly on body N for fetal development. RAF females allocated less body N to calves than did RG females (92% vs. 95% of calf N), which was consistent with the production of calves that were 8% smaller in RAF than in RG. Allocation of body N to milk was also high for both herds, similar at calving for RAF and RG females (88% vs. 91% of milk N, respectively), but lower in RAF than RG females (95% vs. 99% of milk N) at weaning, which was consistent with a small but significantly greater reliance on dietary N supplies to support milk production at weaning. Female caribou used body protein stores to ensure a constant supply of N for fetal growth and milk production that minimized the effects of trophic mismatches on reproduction. The combination of migration and capital investment may therefore allow females to produce calves and attenuate the effects of both temporal and spatial mismatches between vegetation green-up and calf growth, which ultimately would reduce trophic feedbacks on population growth. Our data suggest that small changes in maternal allocation of proteins over the long period of gestation produce significant changes in calf mass as females respond to changes in resources that accompany changes in the size and distribution of the population