Feeding or Resting? The Strategy of Rutting Male Alpine Chamois

Optimal foraging theory suggests that animals normally maximize energy intake to optimize their energy balance. However, when efficiency to assimilate energy falls below the level necessary to ascertain basal energetic requirements, they should shift to an energy saving strategy. Males of many ruminant species considerably reduce their food intake during the rut. Nevertheless, they are commonly assumed to maximize energy intake besides their investments in rutting activities. Based on predictions of optimal foraging theory and the specific ruminant digestive physiology, we propose, however, that rutting males in polygynous species with time consuming mating tactics should instead use an energy saving strategy. Particularly, we predict this to be the case in Alpine chamois (Rupicapra rupicapra rupicapra), a highly polygynous mountain ungulate, of which the males defend mating territories during the rut. By combining observational and telemetry data of eight radio‐collared males we constructed individual 24‐h time budgets, and compared the behavior of males before, during and after the rut. Males spent significantly less time feeding during the rut (0.9 h) compared with before (8.5 h) and afterwards (6.4 and 7.5 h, respectively), whereas time spent lying remained more or less unchanged (pre‐rut; 12.7 h, rut; 13.3 h, post‐rut; 12.9 and 13.9 h, respectively). The ratio of time spent feeding to lying dropped from 0.67 in the pre‐rut period to 0.05 in the rutting period. As a result, males allocated on average approx. 90% of their non‐rutting time to lying, and a negative relationship between rutting and lying time emerged. Hence, males seemed to trade lying time against rutting time. We conclude from these results that male Alpine chamois do not maximize their energy intake during the rut, but rather adopt an energy saving strategy to optimize their energy balance.     

Rut-Induced Hypophagia in Male Bighorn Sheep and Mountain Goats: Foraging Under Time Budget Constraints

In polygynous ungulates, the rut imposes constraints on male time budgets that generate a trade‐off between maintenance and reproduction, leading to a reduction in time spent foraging. As mating activities can incur substantial somatic costs, males are expected to spend their ‘non‐rutting’ time recovering during the breeding season. If the diminution in time allocated to foraging by males is only a consequence of time budget constraints, males should keep a similar ratio of time spent foraging to lying to that observed in the pre‐rut, leading to an overall reduction of these two activities (the ‘foraging constraint’ hypothesis). Alternatively, if males adopt an energy‐saving strategy, they should limit energy expenditures by reducing foraging but not lying time, as the energy gains of forage intake may not meet the basal energetic requirements, especially in northern and temperate regions (the ‘energy‐saving’ hypothesis). Here, we contrast these two hypotheses by comparing individual daily time budgets of marked adult bighorn sheep rams (Ovis canadensis) and male mountain goats (Oreamnos americanus) during the pre‐rut and the rut. Concordant results for both species support the ‘foraging constraint’ hypothesis, as sexually‐active males reduced time spent foraging and lying from the pre‐rut to the rut because of an increase in time spent in mating‐related activities. Bighorn sheep rams also increased time spent foraging when not engaged in mating tactics, providing further support for a ‘maximisation’ of energy intake in the absence of reproductive opportunities. Because there are also known physiological changes that occur during the rut which may cause appetite suppression, for example to produce metabolic compounds linked with olfactory communication (the ‘scent‐urination’ hypothesis) or to cope with increased burden of parasites (the ‘parasite‐induced anorexia’ hypothesis), further research should aim at simultaneously testing these current hypotheses to better understand rut‐induced hypophagia and its effects on the life histories of male ungulates.     

Does a temperate ungulate that breeds in summer exhibit rut-induced hypophagia? Analysis of time budgets of male takin (Budorcas taxicolor) in Sichuan,China

Mammals maximize fitness by optimizing time and energy allocation between reproduction and survival. Describing time budgets is a way to understand a species' constraints in energy allocation. We describe a time budget for male takin (Budorcas taxicolor) in Tangjiahe Nature Reserve, China, to better understand rut-induced hypophagia, which is frequently observed in temperate ungulates that breed in autumn or in winter. Observations generally occurred at two elevations (1200-1600m and 2600-3200m), using 20-min focal animal scan sampling from 2007 to 2009. Feeding behaviors accounted for the majority in takin's time budget (61.1%) during daylight hours, relative to the other observed behaviors, such as rest (14.1%), alert behavior (10.2%) and locomotion (6.8%). We found a negative correlation between feeding behavior and rutting behavior during the rutting season. A ratio of feeding time to resting time increased from pre-rut to rut, while resting behavior did not change significantly across seasons. These results suggest the "energy saving" hypothesis could explain reduced foraging in male takin during the rut, but aspects of the species biology suggest that hypotheses for rut-induced hypophagia developed for other temperate ungulates do not apply to takin. We suggest that the unusual summer rutting season of takin releases males from the energy constraints encountered by temperate ungulates that breed in the autumn and has other benefits for offspring survival. Further research should be conducted on ungulates that exhibit rut during the summer and tropical ungulates that might not experience limited food availability following the mating season to improve our understanding on rut-induced hypophagia.     

Foraging dynamics of muskoxen in Peary Land, northern Greenland

Muskoxen Ovibos moschatus in northern Greenland (79-83°N) are at the northern limit of their distribution and exist under seasonal extremes dominated by nearly 10 months of winter, much of which is without sunlight. The period of summer vegetative growth is less than two months. In the Kap København area (82°30'N), diversity of plant species is low (76 species of vascular plants) and forage biomass in major vegetation types in summer varies from over 40 g m^-2 in sedge-dominated fens to ≤5 g m^-2 in polar barrens. Nonetheless, 90-95% of the ice-free area consists of barren ground or sparcely vegetated polar desert. During summer, muskoxen apparently foraged opportunistically to maximize intake, with sedges the major food item in fens while willows were the major dietary component when on willow-dominated slopes. Quality of summer forage was high during its early phenological stages, with 21-28% crude protein and 60-75% in vitro digestibility. Microhistological analysis of winter feces indicated dominance by graminoids. Muskoxen spent > 50% of their daily activity feeding, which fits a cline of increasing feeding time with increasing latitude in summer. Increased feeding times at high latitudes appears to be a function of both reduced forage biomass and need to maximize forage intake during the brief summer period when forage quality is high. Movement rates in summer while foraging were inversely related to available forage biomass. Seasonal activity of muskoxen peaks during the rutting period (July-September) and then declines gradually through early winter to a low in late winter (March-April).     

Contrasting Alternative Hypotheses to Explain Rut‐Induced Hypophagia in Territorial Male Chamois

Male ungulates in temperate environments often show a severe reduction in time spent foraging during the mating season. Several hypotheses have been put forward to explain this phenomenon but, so far, no study investigated the proximate mechanisms underlying rut‐induced hypophagia in ungulates using alternative mating tactics (AMTs). Between the pre‐rut and post‐rut of 2011 and 2012, we collected data on activity budgets, parasite burden and androgen levels of territorial and non‐territorial male Alpine chamois Rupicapra r. rupicapra in the Gran Paradiso National Park (Italy). We aimed to investigate whether AMTs showed similar reduction in time spent foraging during the mating period and to test the predictions underlying alternative hypotheses that may explain rut‐induced hypophagia. Only territorial males showed a significant reduction in time spent foraging during the rut; the lack of correlation between proportion of time spent foraging and androgen metabolites or parasite burden did not fully support the physiological and the parasite hypotheses, while the foraging constraint, the energy‐saving and the physical rest hypotheses could not be discounted. Territorial males decreased the time spent lying down from the pre‐rut to the rut, but not their foraging‐to‐lying‐down ratio. During the mating period, we found negative correlations between time spent foraging or lying down and time spent rutting. Our data suggest that territorial males’ behaviour is more consistent with the foraging constraint hypothesis than with the energy‐saving hypothesis previously suggested. Yet, during the rut territorial males did not maximise their foraging time, and the optimisation of their energy balance could rather depend upon feeding on relatively high‐quality plants. This suggestion – possibly named ‘forage quality hypothesis’ – now requires further investigations. This work showed that alternative mating behaviours may underlie different patterns of foraging strategies: we suggest that tests of alternative hypotheses to explain rut‐induced hypophagia within ungulate populations should not ignore the occurrence of AMTs.     

To Feed or Not to Feed? Testing Different Hypotheses on Rut‐Induced Hypophagia in a Mountain Ungulate

In many ruminant species, males dramatically reduce forage intake during the rut. To date, different hypotheses have been suggested to explain this rut‐induced hypophagia. To assess the predictions of the main hypotheses, we analysed Alpine ibex (Capra ibex) activity budget and compared the behaviour of males and females before, during, and after the rut. Only males spent significantly less time foraging during the rut than outside of it, whereas females allocated a similar proportion of time to foraging before, during, and after the rut. Our results showed that during the rut males also reduced lying time, while the ratio of time spent feeding to time spent lying did not change for males among periods. In conclusion, during the breeding season males maximized energy intake when not actively engaged in mating activities and rut‐induced hypophagia appeared to result from time budget constraints generated by mating‐related activities. Accordingly, the foraging constraint hypothesis seems appropriate to explain this phenomenon in Alpine ibex males.     

不同发情阶段雄性鹅喉羚的时间分配特征

以往研究表明受发情交配行为制约,一些雄性反刍动物在发情期食物摄入量明显降低。已有两个相关假说解释该现象:能量摄入最大化假说和能量保存假说。作者于2009 ～ 2010 年在卡拉麦里山有蹄类自然保护区研究了雄性鹅喉羚不同发情阶段的时间分配。结果表明雄羚发情期采食时间比例明显下降(37. 9% ),低于发情前期(63. 6% )和发情后期(65. 8% );发情期卧息时间比例(6. 0% )与发情后期相近(5. 4% ),明显低于发情前期(23.2% );发情前期至发情后期采食卧息时间比(分别为2. 7、6. 3、12. 1)显著增加;发情期雄羚站立和移动时间比例明显升高,采食行为时间占非发情行为时间主要部分(86. 4% ),且采食行为与发情行为显著相关。相比之下,雌羚不同发情阶段采食行为时间分配比例相似。总之,除必需投入的发情行为外,发情期雄羚最大化其能量摄入;发情行为的投入是导致发情期雄羚食物摄入量下降的主导因子,雄性能量摄入最大化假说更好地解释了发情期鹅喉羚所采取的能量策略。     

Characteristics of foraging sites and protein status in wintering muskoxen: insights from isotopes of nitrogen

Identifying links between nutritional condition of individuals and population trajectories greatly enhances our understanding of the ecology, conservation, and management of wildlife. For northern ungulates, the potential impacts of a changing climate to populations are predicted to be nutritionally mediated through an increase in the severity and variance in winter conditions. Foraging conditions and the availability of body protein as a store for reproduction in late winter may constrain productivity in northern ungulates, yet the link between characteristics of wintering habitats and protein status has not been established for a wild ungulate. We used a non‐invasive proxy of protein status derived from isotopes of N in excreta to evaluate the influence of winter habitats on the protein status of muskoxen in three populations in Alaska (2005–2008). Multiple regression and an information‐theoretic approach were used to compare models that evaluated the influence of population, year, and characteristics of foraging sites (components of diet and physiography) on protein status for groups of muskoxen. The observed variance in protein status among groups of muskoxen across populations and years was partially explained (45%) by local foraging conditions that affected forage availability. Protein status improved for groups of muskoxen as the amount of graminoids in the diet increased (?0.430 ± 0.31, β± 95% CI) and elevation of foraging sites decreased (0.824 ± 0.67). Resources available for reproduction in muskoxen are highly dependent upon demographic, environmental, and physiographic constraints that affect forage availability in winter. Due to their very sedentary nature in winter, muskoxen are highly susceptible to localized foraging conditions; therefore, the spatial variance in resource availability may exert a strong effect on productivity. Consequently, there is a clear need to account for climate–topography effects in winter at multiple scales when predicting the potential impacts of climatic shifts on population trajectories of muskoxen.     

Foraging time of rutting bighorn rams varies with individual behavior, not mating tactic

Mate guarding is the primary mating tactic used by dominantmales of many species of ungulates. Guarding males are thoughtto forage less during the rut than do nonguarding males, possiblyleading to greater fitness costs. I observed bighorn rams foragingduring the pre-rut and the rut. I compared how coursing (analternative mating tactic) and tending (a form of mate guarding)affected the foraging behavior of bighorn rams over the rut,to test whether foraging was more constrained by mate guardingthan by coursing. All adult males spent less time feeding duringthe rut compared with the pre-rut. The decrease in time spentfeeding, however, was independent of mating tactic. Contraryto expectation, individual rams observed both coursing and tendingspent less time foraging when coursing than when tending. Foryoung rams, the time spent in rutting activities was correlatedwith individual pre-rut mass, indicating that males either modifytheir behavior according to available metabolic reserves oradjust the energy devoted to rutting activities to the levelof expected benefits. Mate guarding does not appear to constrainforaging more than coursing. The costs of male reproductivebehavior may depend more upon individual effort than on theparticular tactic adopted.     

Resource partitioning by mammalian herbivores in the high Arctic

Willow (Salix arctica) and sedges (Carex stans and Eriophorum triste) were the dominant plants available as forage for herbivores in the high Arctic of Greenland. Willow leaves were of high quality as forage in early stages, of phenology, but crude protein and digestibility declined markedly by late stages whereas sedges, remained high in forage quality throughout the growing season. Densities of fecal pellets indicated that muskoxen (Ovibos moschatus) made heaviest use of sedge-dominated vegetation types in both winter and summer, although increased use of willow communities was observed in early summer. Hares (Lepus arcticus) favored willow-dominated communities in both winter and summer. Evidence of collared lemming (Dicrostonyx groenlandicus) winter use was mainly in willow-dominated communities where snow had accumulated, whereas in summer they were present in drier habitas dominated by willows, but with greater plant diversity. Analyses of plant tissues in feces indicated that graminoids composed over 60% of the diet of muskoxen in winter and over 40% in summer. Willows were of nearly equal importance in the muskox diet in summer, and forbs, Dryas integrifolia, and moss collectively composed over 20% of the diet in both summer and winter. Grass accounted for nearly 50% of the diet of hares in both summer and winter, with willows, forbs, and moss accounting for most of the remainder. Willows and graminoids dominated the diet of lemmings, with willows being somewhat more important in summer and graminoids in winter. Moss was a noteworthy dietary component of lemmings. Differences in body and digestive-tract morphology among the three mammalian herbivores account for differences in locomotive efficiency, predator avoidance, and foraging efficiency which interact with vegetation quality, density, and patchiness. The resulting patterns of use of the landscape result in minimal overlap in use of forage resources and help to explain the distribution and co-existence of high Arctic herbivores.     

不同年龄雄性北山羊发情期时间分配特征

前人研究表明,可多次繁殖的反刍物种其雄性个体在发情期采食时间显著减少。目前有两个假说解释这一现象,即能量摄入最大化假说和能量保存假说。为验证雄性北山羊在不同发情阶段所采取的能量保存策略,作者于2014年10-12月在新疆天山中部采用焦点动物取样法采集数据,采用Kruskal-Wallis检验和Spearman秩相关性检验分析数据。研究发现雄性北山羊成体和亚成体发情期采食时间均显著低于发情前期和发情后期,但二者在不同发情阶段卧息时间无显著变化,发情期采食和卧息时间比亦显著降低。发情期发情行为时间显著高于发情前期和发情后期,非发情时间主要用于采食。发情期采食时间和卧息时间都与发情行为时间呈显著的负相关关系。雌性北山羊发情期采食时间亦显著低于发情前期和发情后期,发情期和发情后期卧息时间显著高于发情前期。本研究结果表明,发情期不同年龄阶段雄羊都主要采取能量摄入最大化策略,但同时也具有部分能量保存策略的特征。     

"占群"还是"挑战"?不同时间限制条件下麋鹿个体的交配计策

在麋鹿的发情交配季节 ,雄性麋鹿可区分为 3种类型 :“群主”、“挑战者”和“单身汉”。“群主”是一头圈占并控制雌鹿活动的优势雄性。“挑战者”不占有雌性繁殖群 ,但在发情场附近地点展示炫耀。当雌性繁殖群的雌鹿外出采食靠近“挑战者”的展示炫耀地点时 ,“挑战者”会积极地寻求机会与之交配。“单身汉”在繁殖季节不表现发情行为。他们像非繁殖季节一样采食 ,采食后蹲在水塘中休息。我们对何种因素决定麋鹿个体的发情交配计策感兴趣。 1996至 1998年夏天 ,我们在北京麋鹿苑观察麋鹿发情交配行为以分析导致这些行为差异的原因。结果发现 ,“群主”、“挑战者”和“单身汉”用于维持生命的时间预算与用于发情的时间预算成反比 ,并且 ,“群主”、“挑战者”和“单身汉”用于维持生命的时间预算与用于发情的时间预算差异显著。“群主”的绝大部分时间用于发情占群 ,而用于采食、饮水的时间很少 ,所以 ,“群主”在发情期间基本上处于禁食状态 ,靠消耗体内脂肪维持生命。“单身汉”则相反 ,绝大部分时间用于采食、休息和反刍 ,基本上没有发情行为。“挑战者”在发情行为与维持生命行为之间的时间则居于“群主”与“单身汉”之间。交配次数是偏态分布的 ,与雄性发情时间呈正比。“群主”的交配概率最高     

Selectivity underlies the dissociation between seasonal prey availability and prey consumption in a generalist predator

Generalist predators are capable of selective foraging, but are predicted to feed in close proportion to prey availability to maximize energetic intake especially when overall prey availability is low. By extension, they are also expected to feed in a more frequency‐dependent manner during winter compared to the more favourable foraging conditions during spring, summer and fall seasons. For 18 months, we observed the foraging patterns of forest‐dwelling wolf spiders from the genus Schizocosa (Araneae: Lycosidae) using PCR‐based gut‐content analysis and simultaneously monitored the activity densities of two common prey: springtails (Collembola) and flies (Diptera). Rates of prey detection within spider guts relative to rates of prey collected in traps were estimated using Roualdes’ c_st model and compared using various linear contrasts to make inferences pertaining to seasonal prey selectivity. Results indicated spiders foraged selectively over the course of the study, contrary to predictions derived from optimal foraging theory. Even during winter, with overall low prey densities, the relative rates of predation compared to available prey differed significantly over time and by prey group. Moreover, these spiders appeared to diversify their diets; the least abundant prey group was consistently overrepresented in the diet within a given season. We suggest that foraging in generalist predators is not necessarily restricted to frequency dependency during winter. In fact, foraging motives other than energy maximization, such as a more nutrient‐focused strategy, may also be optimal for generalist predators during prey‐scarce winters.     

内蒙古达赉湖地区蒙原羚繁殖期及其前后昼间行为时间分配及能量平衡策略

2007年11月、12月和2008年3月,在内蒙古达赉湖地区,采用扫描取样法对雌雄蒙原羚繁殖期及其前后昼间行为时间分配进行了研究。 研究表明：（1）繁殖期前、繁殖期和繁殖期后,雌性蒙原羚采食时间,占昼间活动时间的比例分别为（44.9±3.8）%、（43.5±4.0）% 和 (46.2±3.1)%;卧息时间,占昼间活动时间的比例分别 为（32.3±4.8）%、（29.2±2.9）% 和 (28.0±4.8)%;雌性蒙原羚在繁殖期及其前后采食、移动和卧息的行为时间分配差异不显著（P>0.05）,站立、繁殖、“其他”行为时间分配差异性显著（P<0.05）。（2）繁殖期前、繁殖期和繁殖期后, 雄性蒙原羚采食时间,占昼间活动时间的比例分别为 (52.6±3.8)%、(17.5±2.8)% 和 (29.8±4.8)%;卧息时间,占昼间活动时间的比例分别为 (13.4±6.4)%、(24.2±4.1)% 和 (44.2±4.7)%。雄性蒙原羚在繁殖期及其前后采食、卧息、站立、移动、繁殖、“其他”时间分配均有显著差异（P<0.05）。动物采食卧息的行为时间分配反映动物的能量平衡策略。雌性蒙原羚的时间分配表明,雌性蒙原羚的能量平衡策略在繁殖期前、繁殖期和繁殖期后没有发生显著变化,均为能量摄入最优化策略,尽可能多的时间分配在采食上;雄性蒙原羚的时间分配表明,在繁殖期前,其能量平衡策略为能量摄入最优化策略,尽可能多的时间分配在采食上;雄性蒙原羚繁殖期及繁殖期后其能量平衡策略转变为能量支出优化策略,尽可能少的支出能量,尽可能多的时间分配在卧息上。     

Strategic (adaptive) hypothermia in bull dromedary camels during rut; could it increase reproductive success?

In this study of body temperatures (T_b) in free ranging dromedary camels, we found that bulls in rut start the days cooler. Daily minima during rut averaged 0.6°C lower than at other times (95% CI 0.27–0.94°C) and daily maxima averaged 0.45°C higher (95% CI −0.01 to –0.91°C), increasing the daily T_b cycle. Knut Schmidt-Nielsen described a similar pattern in captive dromedaries deprived of water in hot conditions, which he interpreted as a strategy to conserve water. Our observations were made in winter and with water freely available. Dromedaries can apparently employ heterothermy for more than just water conservation. In the strenuous daily contests between rival bulls in rut, a lower T_b early in the day should extend the time for which a contestant can challenge or defend before heat stress becomes a problem. Calculations show that lowering T_b by even 0.6°C extends that time by more than 30 min, and many daily minima during rut were lower than that. Because the eventual winner of contests gains or retains a herd of females, we speculate that cooler T_b at the start of daily contests confers an advantage which translates directly into increased reproductive success.     

Seasonal migration of male red deer (<Emphasis Type="Italic">Cervus elaphus</Emphasis>) in southern Sweden and consequences for management

Red deer Cervus elaphus is a highly appreciated and intensively managed game species throughout Europe. A common management objective is a sustainable harvest of large trophies. In southern Sweden, management has mainly aimed at preserving the nominate subspecies C. elaphus elaphus. Seasonal migration of red deer males may, however, complicate both harvest management as well as conservation efforts. I used individually identified male red deer in southern Sweden to observe distance travelled from rutting areas to areas used by males in summer and winter. Adult males were identified by antler shape and photo-documented during rut. Photos from the rut were compared to trophies of deer harvested or found dead, to found cast antlers and to stags photographed during summer. From 1969 to 2007, a distance between rutting ground and summer/winter quarters was established for 96 identified stags. An average distance of 14 km and a maximum distance of 47 km were recorded between rut and summer/winter observations. The seasonal migration of males increases the risk of overexploitation of males with harvest in both rutting areas and wintering areas. Harvest management and conservation efforts may fail if males seasonally migrate outside the management unit. The results suggest that seasonal migration must be considered in harvest management and conservation and that there is a need for a regulation of male harvest. Furthermore, the study stresses that the success in deer management of single hunting units, may be largely dependent on the harvest policies in the near surroundings as well as in areas tenths of kilometres away, suggesting that a successful management must rely on co-operation and co-ordination on a landscape scale.     

Assessing the nutritional consequences of switching foraging behavior in wood bison

Diet is one of the most common traits used to organize species of animals into niches. For ruminant herbivores, the breadth and uniqueness of their dietary niche are placed on a spectrum from browsers that consume woody (i.e., browse) and herbaceous (i.e., forbs) plants, to grazers with graminoid‐rich diets. However, seasonal changes in plant availability and quality can lead to switching of their dietary niche, even within species. In this study, we examined whether a population of wood bison (Bison bison athabascae) in northeast Alberta, Canada, seasonally switched their foraging behavior, and if so, whether this was associated with changes in nutrient acquisition. We hypothesized that bison should switch foraging behaviors from grazing in the winter when standing, dead graminoids are the only foliar plants readily available to browsing during spring and summer as nutritious and digestible foliar parts of browse and forbs become available. If bison are switching foraging strategy to maximize protein consumption, then there should be a corresponding shift in the nutritional niche. Alternatively, if bison are eating different plants, but consuming similar amounts of nutrients, then bison are switching their dietary niche to maintain a particular nutrient composition. We found wood bison were grazers in the winter and spring, but switch to a browsing during summer. However, only winter nutrient consumption of consumed plants differed significantly among seasons. Between spring and summer, bison maintained a specific nutritional composition in their diet despite compositional differences in the consumed plants. Our evidence suggests that bison are selecting plants to maintain a target macronutrient composition. We posit that herbivore''s can and will switch their dietary niche to maintain a target nutrient composition.     

Nutritional Value of Moss for Arctic Ruminants: a Test with Muskoxen

Abstract: Although moss is commonly found in the feces of arctic herbivores, we do not know the digestible value of this forage for ruminants. We compared grass hay (Bromus sp.) with moss (Hylocomium splendens, Tomenthypnum nitens) from 2 locations in Alaska, USA: Cape Krusenstern National Monument and Fairbanks. We evaluated forages by digestion in ruminally fistulated muskoxen (Ovibos moschatus) by suspending forages in polyester bags before and after the rumen was acclimated with moss for 15 consecutive days. Ruminal degradation was not affected by acclimation to moss. Hay lost dry matter during 48 hours of ruminal incubation (-49%), whereas moss gained dry matter (+44-57%). Incubated moss gained nitrogen (+435-680%), as well as fiber (+18%), and one moss gained ash (+121%). Mass gained by moss in the rumen was probably due to the combined effect of microbial colonization and adsorption of fibrous particles onto the sponge-like matrix. We evaluated postruminal degradation of forages by incubation in acid-pepsin. Ruminally incubated mosses lost little nitrogen in acid-pepsin even though ruminally incubated hay lost 23% nitrogen on acid digestion. Consumption of moss during winter may be a net cost of selecting plants within moss communities when lichens and graminoids are scarce. Moss in feces may, therefore, indicate low availability of favored foods for muskoxen and other arctic ruminants that are confined to small winter ranges. Increasing concentrations of moss in the feces and, thus, the diet of muskoxen may alert wildlife managers to shifts in winter range quality or forage access due to changing snow conditions.     

Contributions of winter foraging to the annual growth of thermally dissimilar fish species

The seasonal energy dynamics of temperate fishes will likely be affected by climate change, especially during the winter. Few studies, however, have focused on winter. Fishes are more active in winter than previously thought, thus, an inquiry into the energetic contributions of winter foraging to the annual growth of fishes is needed given expected changes in winter conditions. We used stomach content data, total lipid analyses, and bioenergetics modeling to assess the effects of winter foraging on three species in Lake Champlain, Vermont, USA. We compared species in two thermal guilds, the cool-water species yellow perch (Perca flavescens) and two warm-water species, pumpkinseed (Lepomis gibbosus) and bluegill (Lepomis macrochirus). Our results indicate that winter energy dynamics likely depend on the thermal preference of individual fish species – the cool-water species foraged in all seasons whereas the two warm-water species foraged only in the open-water seasons. In addition, winter foraging provided sufficient energy for overwinter growth in cool-water species but not in warm-water species. Climate change will affect the seasonal energy dynamics that these species have evolved to survive winter conditions in temperate lakes. Thus, we expect climate change to affect individual survival and reproductive success.

     

Daily activity and minimum food requirements during winter for gentoo penguins (Pygoscelis papua) in the South Shetland Islands, Antarctica

Estimates of daily activity and consequent demand for food during winter are scarce for many polar seabirds, yet essential for assessing constraints on foraging effort, demand for food, and potential competition with local fisheries. We affixed archival temperature tags to gentoo penguins (Pygoscelis papua) from two colonies in the South Shetland Islands to measure the frequency, timing, and duration of foraging trips and to estimate minimum food requirements during winter. Foraging trip frequencies ranged from 0.85 to 1.0 trips day⁻¹ and were positively correlated with day length. Early winter foraging trips more closely matched day length than late winter foraging trips. The data suggest that individuals maximize foraging time during the early winter period, likely to recover body mass following the breeding season and molt. The more attenuated response of foraging trip durations to increasing day length in late winter may be related to differences in local resource availability or individual behaviors prior to the upcoming breeding season. Minimum food requirements also exhibited a seasonal cycle with a mid-winter minimum. On average, minimum food requirements were estimated at 0.70 ± 0.12 kg day⁻¹. Extrapolated to the regional population of gentoo penguins, winter food requirements by gentoo penguins were equivalent to roughly 33% of annual krill catches by commercial fisheries in the South Shetland Island region over the past decade. Current expansion of the gentoo population and the krill fishery in the southern Scotia Sea warrants continued monitoring of gentoo penguins during winter.