Each spring, migratory herbivores around the world track or ‘surf’ green waves of newly emergent vegetation to distant summer or wet‐season ranges. This foraging tactic may help explain the great ...abundance of migratory herbivores on many seasonal landscapes. However, the underlying fitness benefits of this life‐history strategy remain poorly understood. A fundamental prediction of the green‐wave hypothesis is that migratory herbivores obtain fitness benefits from surfing waves of newly emergent vegetation more closely than their resident counterparts. Here we evaluate whether this behavior increases body‐fat levels – a critically important correlate of reproduction and survival for most ungulates – in elk Cervus elaphus of the Greater Yellowstone Ecosystem. Using satellite imagery and GPS tracking data, we found evidence that migrants (n = 23) indeed surfed the green wave, occupying sites 12.7 days closer to peak green‐up than residents (n = 16). Importantly, individual variation in surfing may help account for up to 6 kg of variation in autumn body‐fat levels. Our findings point to a pathway for anthropogenic changes to the green wave (e.g. climate change) or migrants’ ability to surf it (e.g. development) to impact migratory populations. To explore this possibility, we evaluated potential population‐level consequences of constrained surfing with a heuristic model. If green‐wave surfing deteriorates by 5–15 days from observed, our model predicts up to a 20% decrease in pregnancy rates, a 2.5% decrease in population growth, and a 30% decrease in abundance over 50 years. By linking green‐wave surfing to fitness and illustrating potential effects on population growth, our study provides new insights into the evolution of migratory behavior and the prospects for the persistence of migratory ungulate populations in a changing world.
Migration is a striking behavioral strategy by which many animals enhance resource acquisition while reducing predation risk. Historically, the demographic benefits of such movements made migration ...common, but in many taxa the phenomenon is considered globally threatened. Here we describe a long-term decline in the productivity of elk (
Cervus elaphus
) that migrate through intact wilderness areas to protected summer ranges inside Yellowstone National Park, USA. We attribute this decline to a long-term reduction in the demographic benefits that ungulates typically gain from migration. Among migratory elk, we observed a 21-year, 70% reduction in recruitment and a 4-year, 19% depression in their pregnancy rate largely caused by infrequent reproduction of females that were young or lactating. In contrast, among resident elk, we have recently observed increasing recruitment and a high rate of pregnancy. Landscape-level changes in habitat quality and predation appear to be responsible for the declining productivity of Yellowstone migrants. From 1989 to 2009, migratory elk experienced an increasing rate and shorter duration of green-up coincident with warmer spring-summer temperatures and reduced spring precipitation, also consistent with observations of an unusually severe drought in the region. Migrants are also now exposed to four times as many grizzly bears (
Ursus arctos
) and wolves (
Canis lupus
) as resident elk. Both of these restored predators consume migratory elk calves at high rates in the Yellowstone wilderness but are maintained at low densities via lethal management and human disturbance in the year-round habitats of resident elk. Our findings suggest that large-carnivore recovery and drought, operating simultaneously along an elevation gradient, have disproportionately influenced the demography of migratory elk. Many migratory animals travel large geographic distances between their seasonal ranges. Changes in land use and climate that disparately influence such seasonal ranges may alter the ecological basis of migratory behavior, representing an important challenge for, and a powerful lens into, the ecology and conservation of migratory taxa.
Populations of woodland caribou (Rangifer tarandus caribou) are declining throughout their range and many are at risk of extirpation, yet the role of nutrition in these declines remains poorly ...understood, in part owing to a lack of information about available nutritional resources during summer. We quantified rates of intake of digestible protein and digestible energy by tame caribou foraging in temporary enclosures in the predominant plant communities of northeastern British Columbia, Canada, during summer–autumn and compared intake rates to daily requirements for protein and energy during lactation. We tested hypotheses related to the nutritional adequacy of the environment to support nutritional requirements during lactation (with and without replenishment of body reserves) and simulated scenarios of foraging by caribou in these plant communities to better understand how wild caribou could meet nutritional demands on these landscapes. Nutritional resources varied among plant communities across seasonal, ecological, and successional gradients; digestible energy intake per minute and per day were significantly greater in younger than older forests; dietary digestible energy and per‐minute and daily intake of digestible protein were greater, though not significantly so, in younger than older forests; and dietary digestible protein was greater in older than younger forests, though differences were not significant. Tame caribou were unable to satisfy protein and energy requirements during lactation, even without replenishment of body reserves, at most sites sampled. Further, foraging simulations suggested widespread nutritional inadequacies on ranges of wild caribou. Selection for habitats offering the best nutrition may mitigate some nutritional inadequacies, but given low availability of vegetation communities with high nutritional value, performance (e.g., calf production, growth, replenishment of body fat and protein) of caribou may be depressed at levels of nutrition documented herein. Our results, coupled with recent measurements of body fat of wild caribou in northeastern British Columbia, refute the hypothesis that the nutritional environment available to caribou during summer in northeastern British Columbia is adequate to fully support nutritional demands of lactating caribou, which has implications to productivity of caribou populations, recovery, and conservation.
Nutritional resources available to caribou in northeastern British Columbia, Canada, during summer–autumn 2013–2015 were variable and largely inadequate to support nutritional requirements during lactation and for replenishment of body protein and fat reserves, thereby potentially constraining individual performance with implications to population productivity. Critical habitat designations corresponded poorly with nutritional value of caribou habitats in summer and early autumn.
High-quality habitats for caribou (Rangifer tarandus (L., 1758)) are associated primarily with lichens, but lichens alone fail to satisfy summer nutritional requirements. To evaluate the summer ...forage value of plant communities across northeastern British Columbia (BC), where populations of northern and boreal ecotypes of caribou are declining, we observed foraging by tame, female caribou. We compared diet composition with forage abundance to determine forage selection and to quantify forage availability. Deciduous shrubs, not lichens, largely dominated summer diets. Caribou were highly selective foragers, with 28 species comprising 78% of diets. Caribou avoided ≥50% of understory vegetation in all communities, especially conifers, evergreen shrubs, mosses, and two genera of terrestrial lichens. Availability of accepted forage (species not avoided) was strongly heterogeneous across landscapes. Alpine shrub areas and mid-elevation spruce–fir stands in the mountains, as well as treed rich fens and white spruce communities in the boreal forests, provided the greatest quantities of accepted forage for caribou. Dry alpine sites and unproductive black spruce communities provided the least accepted forage. Our work has direct implications to caribou conservation by contributing to a greater understanding of the forage value of summer habitats, with implications to habitat selection, seasonal movements, and distribution ecology.
Foraging by animals is hypothesized to be state-dependent, that is, varying with physiological condition of individuals. State often is defined by energy reserves, but state also can reflect ...differences in nutritional requirements (e.g., for reproduction, lactation, growth, etc.). Testing hypotheses about state-dependent foraging in ungulates is difficult because fine-scale data needed to evaluate these hypotheses generally are lacking. To evaluate whether foraging by caribou (Rangifer tarandus) was state-dependent, we compared bite and intake rates, travel rates, dietary quality, forage selection, daily foraging time, and foraging strategies of caribou with three levels of nutritional requirements (lactating adults, nonlactating adults, subadults 1–2 years old). Only daily foraging times and daily nutrient intakes differed among nutritional classes of caribou. Lactating caribou foraged longer per day than nonlactating caribou—a difference that was greatest at the highest rates of intake, but which persisted even when intake was below requirements. Further, at sites where caribou achieved high rates of intake, caribou in each nutritional class continued foraging even after satisfying daily nutritional requirements, which was consistent with a foraging strategy to maximize energy intake. Foraging time by caribou was partially state-dependent, highlighting the importance of accounting for physiological state in studies of animal behavior. Fine-scale foraging behaviors may influence larger-scale behavioral strategies, with potential implications for conservation and management.
Ecological theory predicts that the diffuse risk cues generated by wide‐ranging, active predators should induce prey behavioural responses but not major, population‐ or community‐level consequences. ...We evaluated the non‐consumptive effects (NCEs) of an active predator, the grey wolf (Canis lupus), by simultaneously tracking wolves and the behaviour, body fat, and pregnancy of elk (Cervus elaphus), their primary prey in the Greater Yellowstone Ecosystem. When wolves approached within 1 km, elk increased their rates of movement, displacement and vigilance. Even in high‐risk areas, however, these encounters occurred only once every 9 days. Ultimately, despite 20‐fold variation in the frequency of encounters between wolves and individual elk, the risk of predation was not associated with elk body fat or pregnancy. Our findings suggest that the ecological consequences of actively hunting large carnivores, such as the wolf, are more likely transmitted by consumptive effects on prey survival than NCEs on prey behaviour.
Increased consumer concern for animal welfare has led some poultry producers to alter their stunning methods from electrical to controlled atmosphere stunning. The potential for different impacts on ...meat quality between commercially applied controlled atmosphere stunning (CAS) and electrical stunning (ES) using current US parameters needs further evaluation. Three trials were conducted in a commercial broiler processing facility that uses separate processing lines for ES and CAS. Blood glucose concentrations were measured from broilers stunned by either CAS or ES at: 1) lairage, 2) pre-stunning, and 3) post-stunning, using a glucose monitor. Occurrence of visible wing damage was evaluated post-defeathering and breast fillet meat quality was evaluated through measurement of pH, color, and drip loss at deboning and after 24 h. Data were analyzed using GLM or chi-square with a significance at P ≤ 0.05 and means were separated by Tukey's HSD. Blood glucose concentrations (mg/dL) from CAS and ES birds were not different at lairage (284, 272, P = 0.2646) or immediately prior to stunning (274, 283, P = 0.6425). Following stunning and neck cut, circulating blood glucose from birds stunned by CAS was higher than ES (418, 259, P < 0.0001). CAS carcasses had more visible wing damage than ES carcasses (3.6%, 2.2%, P < 0.0001). Breast fillet pH was lower, L* was higher, and a* was lower at debone for CAS fillets (5.81, 54.65, 1.96) compared to ES fillets (5.92, 53.15, 2.31, P < 0.0001, P = 0.0005, P = 0.0303). Drip loss did not differ between breast fillets from CAS or ES broilers (4.83, 4.84; P = 0.0859). The implications of increased blood glucose concentration post-CAS are unknown and require further evaluation. However, the increase in visible wing damage observed post-defeathering from CAS carcasses indicated a need for equipment parameter adjustments during the process from stunning through defeathering when using CAS for broiler stunning. Although differences were observed in breast fillet attributes at deboning, these differences would have minimal practical application and were no longer present at 24 h. Overall, use of CAS in a commercial facility resulted in differences in subsequent product quality when compared to ES.
Evaluating nutritional condition provides insights of nutritional influences on wildlife populations. We sampled three measures of condition — body fat, body mass, and loin thickness — of adult ...female caribou (Rangifer tarandus (Linnaeus, 1758)) in boreal settings in the Northwest Territories (NT), Canada, in December and March, 2016–2018, and in mountain and boreal settings in British Columbia (BC), Canada, in December and February, 2014–2015. We evaluated the effect of calf-rearing on condition in December, compared influences of summer–autumn versus winter on condition over winter, and developed an annual profile of nutritional condition with estimates from caribou dying in summer. Mean December body fat was 8.4% in females with calves and 11.4% in females without calves, demonstrating the influence of lactation on condition. Over winter, nutritional condition did not decline in northeastern BC and it declined slightly in NT: body fat by 0.55 percentage points, mass by 2.8 kg, and loin thickness did not change. Body fat peaked in December, changed little over winter, but declined to a minimum by early summer, temporally coinciding with elevated rates of adult female mortality. Consistent with those of other ungulate studies worldwide, our findings suggest a need to focus on nutritional limitations operating in late spring through early autumn.
Elk (Cervus elaphus) in the western United States are an economically and socially valuable wildlife species. They have featured species status for federal land management planning; hence, ...considerable modeling focused on habitat evaluation and land management planning has been undertaken for elk. The extent to which these and other habitat models for large ungulates account for influences of nutritional resources varies greatly, probably because of varying recognition of the importance of nutrition and uncertainty about how to measure and model nutrition. Our primary goals were to 1) develop greater understanding of how habitat conditions influence foraging dynamics and nutrition of elk in summer and autumn; and 2) illustrate an ecological framework for evaluating and predicting nutritional resources so that nutritional needs of elk can be integrated within landscape-scale plans, population models, and habitat evaluation models. We evaluated foraging responses of elk to clearcut logging and commercial thinning, forest succession, and season across ecological site potentials. We also identified the extent to which plant communities satisfied nutritional requirements of lactating female elk and their calves. Our study was conducted in the temperate rainforests of the Pacific Northwest on industrial and public timberlands. We evaluated relations between habitat conditions and elk nutrition in plant communities representing a range in stand age and ecological conditions at 3 study areas, 1 near the Canadian border in the north Cascades Mountains (Nooksack), 1 in the Coast range southwest of Olympia, Washington (Willapa Hills), and the third in the central Cascades near Springfield, Oregon (Springfield), from late June to November, 2000–2002. In 98–143 macroplots per study area, we measured forage abundance by plant species, digestible energy content by plant life-form group, and forest overstory. In a subset of these macroplots (∼30 per study area), we held 4 tame lactating elk with calves in electrified pens (n = 15–25 adult elk per year), and sampled activity budgets, dietary composition, forage selection, and other measures of foraging behavior; dietary digestible energy (DE; kcal/g) and protein (DP; %) levels; and intake rates of these nutrients. In 15 of these pens, we held elk for extended periods (13–21 days) to monitor changes in body fat of adults and growth of calves. We developed equations to predict dietary DE and DP and per-minute intake rates of each in a nutrition prediction model that reflected vegetation attributes and ecological site influences. Total abundance of forage in the western hemlock series after clearcut logging in low to moderate elevations (≤1,000 m) ranged from a peak of 3,000–4,500 kg/ha in 5- to 10-year-old stands to 100–300 kg/ha in 20- to 50-year-old stands with only moderate increases through late succession. Patterns were similar in higher elevation forests (1,000–1,800 m), although peaks and troughs in forage abundance developed more slowly. Deciduous shrubs, forbs, and graminoids were abundant in early seral stages after stand disturbance, but these were rapidly replaced by shade-tolerant evergreen shrubs and ferns as conifer overstories closed 15–20 years later in low-elevation forest zones, and 20–40 years later in high-elevation zones. Digestible energy within plant life-form groups generally declined with season and with advancing succession, increased with elevation, and was highest in forbs and deciduous shrubs and lowest in evergreen shrubs and shade-tolerant ferns. Levels of DE in elk diets exhibited a strong asymptotic relation with abundance (kg/ha) of plant species that were eaten in proportions equal to or greater than availability (i.e., accepted species). Marked declines in dietary DE occurred in stands containing <400 kg/ha to 500 kg/ha of accepted species, largely because elk began to increase consumption of avoided species, and these typically contained low levels of DE. The asymptotic pattern was generally consistent among seasons, study areas, and habitat types (potential natural vegetation categories), although the asymptote averaged 10–12% greater in high- versus low-elevation forests. Abundance of accepted species in early seral stands averaged 7–10 times that in mid and late seral stages, and dietary DE levels varied accordingly. Dietary DE was little influenced by thinning in 20- to 60-year-old stands. In contrast, levels of dietary DP were unrelated to forage composition and abundance of accepted or avoided species, and varied little between low and high-elevation forests. Dietary DP increased with overstory canopy cover, was higher in thinned and hardwood stands, particularly those hardwood stands with saturated soils in late summer, declined with season, and was lowest in the driest forest communities in our study. Overall, soil moisture regime and season accounted for the majority of variation in dietary DP. Relations between nutrient intake rate and vegetation conditions varied among study areas and habitat types. Nevertheless, elk maintained about double the intake rate of DE in early seral stages versus closed-canopy forests. Intake rate of DP was similar between early seral versus closed-canopy forests, despite modestly lower dietary DP in early seral stages. Protein intake rate was greater in thinned and hardwood-riparian stands. In early seral stages, dietary DE typically met the requirement of 2.7 kcal/g of ingested forage (necessary to maintain body fat levels of lactating elk in summer) in the low-elevation forest zones and exceeded that level in high-elevation forest zones. In closed-canopy forests, dietary DE averaged below requirements, markedly so in low-elevation forests (2.25–2.5 kcal/g) and moderately so in high-elevation forests (2.4–2.65 kcal/g). Evidence of deficiencies based on DE intake rate was greater, averaging about 50% of requirements (28 kcal/min; 21,000 kcal/day) in closed-canopy forests and 80% of requirements in early seral stages. In contrast, dietary DP and DP intake rates generally approached or exceeded estimated requirements (6.8% DP; 380 g/day) in many habitat types that we sampled, with the greatest potential for deficient DP intake rates in relatively dry, low-elevation forests. Body fat dynamics and growth of calves confirmed nutritional deficiencies suggested by our data on DE intake. Adult elk lost body fat during all trials at rates generally in accordance with expectations at the dietary DE levels they consumed, and rate of change in body fat was inversely related to abundance of accepted species. Calves grew at about half the rate of which they are capable (1 kg/day) if summer nutrition is sufficient. Daily calf growth was positively related to their mother's dietary DE and protein intake levels. Elk compensated for limited foraging options in many plant communities via several behavioral strategies. Selection was generally strong for plants with higher DE levels, where selected species composed nearly 5 times more of the diet than did species that elk avoided, yet avoided species were 10 times more abundant. As abundance of accepted species declined below approximately 400 kg/ha, elk increased intake of avoided species. This strategy delayed declines in per-minute forage and DE intake rate as long as abundance of accepted species remained above roughly 200 kg/ha, despite declining dietary DE levels apparent at <400 kg/ha to 500 kg/ha of accepted species. Elk traveled faster while foraging to compensate for plant communities with very low abundance of total forage, increased bite rate as bite mass declined, increased time spent feeding at night in pens with low abundance of total forage or relatively low dietary DE levels, and increased rumination time particularly as dietary fiber levels increased. Dietary DE, DP, and intake rates of these nutrients therefore were robust to substantial variation in overall forage quality and quantity. Nevertheless, these strategies were insufficient to compensate for low abundance of high-quality forage typically present under closed forest canopies. Our nutrition model included nonlinear and multiple regression equations to predict 1) dietary DE (kcal/g of ingested forage), based primarily on abundance of accepted species (r2 = 0.49–0.62); and 2) dietary DP (% of ingested forage), based primarily on abundance of accepted species, overstory canopy cover, and site characteristics intended to index soil moisture (r2 = 0.60). Additional equations to predict intake rates per minute included the same covariates, but the variance explained was modestly lower (DE intake: r2 = 0.43; DP intake: r2 = 0.45–0.54). With these equations, we created nutrition-succession profiles to illustrate dietary DE and DP intake dynamics across the successional sequence for each habitat type and study area. These profiles may serve as inputs for spatially explicit maps of nutritional resources for elk. Because they were developed using nutrition data from foraging elk, they should help alleviate much of the uncertainty arising from proxy variables often used as indices of nutritional resources. Our data demonstrated that nutritional resources in forests of western Oregon and Washington are generally deficient for lactating elk in summer and early autumn. They provided evidence that inadequate nutritional resources are largely responsible for low body fat in autumn and reduced pregnancy rates reported for many elk herds in the Pacific Northwest. Our data also illustrated that nutritional value of habitats is highly variable depending on ecological context, disturbance, and succession. Thus, how, if, and where forested elk habitats are managed can greatly influence the nutritional suitability of an area. Finally, our data indicate a considerable need for integrating nutritional assessments in landscape planning processes where maintaining abundant and productive elk populations is one of several
Offshore wind farms (OWFs) are a key part of efforts to mitigate the impacts of climate change. However, they have the potential to negatively impact seabird species through collisions with turbine ...blades, displacement from preferred foraging habitat and the perception of wind farms as a barrier to migrating or foraging birds. Whilst the data available to model these impacts are increasing, many data gaps remain, particularly in relation to the impacts of barrier effects. We analyse the movements of Sandwich terns in relation to an offshore wind farm cluster using data collected as part of a multi-year GPS tracking study. Over the course of the study, two additional wind farms were built within the home range of the breeding colony. The construction of these wind farms coincided with a change in the foraging and commuting areas used by breeding terns. Whilst birds entered OWFs when foraging, they appeared to avoid them when commuting, driving an apparent ‘funnelling’ effect to important feeding locations. We discuss if this could be driven by changes to the prey base, subsequent displacement and potentially altered routes reflecting new favourable airflow patterns following OWF construction. Our results suggest that behavioural responses of birds to OWFs may be the result of a complex series of ecological and environmental interactions, as opposed to simplistic assumptions around the perception of the OWF as a barrier to movement.
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