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At least 19 recordsLinked to original sources
USGS1980

The natural food habits of grizzly bears in Yellowstone National Park, 1973-74

The natural food habits of grizzly bears ( Ursus arctos horribilis Ord) in Yellowstone National Park were investigated in 1973-74 to identify the grizzly's energy sources and trophic level(s), nutrient use, and distribution. Food consumption was determined by scat analysis and field observations. Food quality and digestibility were estimated by chemical analysis. Grizzlies were distributed in 3 distinctive feeding economies: valley / plateau , a grass/rodent economy where grizzlies were intensive diggers; mountain , primarily a grass/springbeauty/root economy where grizzlies were casual diggers; and lake , primarily a fish/grass economy where grizzlies were fishers. The economies occurred in areas with fertile soils; distribution of bears within each was related to the occurrence of succulent plants. The feeding cycle in the valley/plateau and mountain economies followed plant phenology. Grizzlies fed primarily on meat before green-up and on succulent herbs afterwards; meat, corms, berries, and nuts became important during the postgrowing season. Succulent grasses and sedges with an importance value percentage of 78.5 were the most important food items consumed. Protein from animal tissue was more digestible than protein from plant tissue. Storage fats were more digestible than structural fats. Food energy and digestibility were directly related. Five principle nutrient materials (listed with their percentage digestibilities) contributed to total energy intake: protein from succulent herbs, 42.8; protein and fat from animal material, 78.1; fat and protein from pine nuts, 73.6; starch, 78.8; and sugar from berries and fruits, digestibility undetermined. Protein from succulent herbs, with a nutritive value percentage of 77.3, was the grizzlies' primary energy source. Because succulent, preflowering herbs had higher protein levels than dry, mature herbs, grizzly use of succulent herbs guaranteed them the highest source of herbaceous protein. Low protein digestibility of succulent herbs was compenstated for by high intake. Grizzlies were digestively flexible and maximized use of protein from plant and animal sources. They were adapted to the most constant and abundant sources of protein: succulent herbs and animal material from open, fertile grasslands. Competition among grizzlies for animal food during the pregrowing season may be regulatory for the grizzly population. The grizzly population level can be partially accounted for by the grizzlies' status as secondary consumers during pregreen-up periods and primary consumers during the growing and postgrowing seasons. The essential environmental requirement was the availability of fertile grasslands and herblands interspersed with cover and capable of maintaining artiodactyls, rodents, and abundant nutritious herbs as sources of food.

Yellowstone National Park↗
USGS1984

Proper expression of metabolizable energy in avian energetics

We review metabolizable energy (ME) concepts and present evidence suggesting that the form of ME used for analyses of avian energetics can affect interpretation of results. Apparent ME (AME) is the most widely used measure of food energy available to birds. True ME(TME) differs from AME in recognizing fecal and urinary energy of nonfood origin as metabolized energy. Only AME values obtained from test birds fed at maintenance levels should be used for energy analyses. A practical assay for TME has shown that TME estimates are less sensitive than AME to variation in food intake. The TME assay may be particularly useful in studies of natural foods that are difficult to obtain in quantities large enough to supply test birds with maintenance requirements. Energy budgets calculated from existence metabolism should be expressed as kJ of AME and converted to food requirements with estimates of metabolizability given in kJ AME/g.

Condor↗
USGS2024

No evidence hunting bait increases American black bear population growth in Maine, USA

American black bear ( Ursus americanus ) populations are increasing throughout much of North America. Use of multiple harvest methods, including hunting over bait, is intended to increase harvest success rates to meet harvest and population management objectives. However, black bear population growth can be influenced by food availability, and some speculate the use of bait may inadvertently increase bear abundance through food resource supplementation. We collected hair from black bears captured from 2005–2019 and a selection of potential food items, including those used as bait from 3 study areas in Maine, USA, with different levels of human influence. We used stable isotope analysis of the black bear hair and food item samples to evaluate the contribution of different identified food groups to the diet of individual bears. We found no evidence that greater contribution of human food resources, including bait, increased the number of cubs per litter for reproductive females or that human foods comprised a greater part of the diet in years when natural food resources were less abundant. Approximately 69% of black bear harvest occurred over bait. We found the probability of reproductive-age females to be harvested increased with average representation of human foods with high carbon enrichment (including bait) in their diet, but the relationship was weak, likely because of sampling constraints. Additionally, the probability of being harvested was greater in years when natural food resources were scarce. We conclude that bait is not available on the landscape in large enough amounts or for a sufficient amount of time in Maine to substantially influence female reproduction. Our results indicate hunting over bait is an effective tool in a state that is attempting to maintain a stable bear population via harvest, and dispels conjecture that hunting over bait may increase cub production and offset the intention of harvest.

Maine↗
USGS2024

A systematic review of the effects of climate variability and change on black and brown bear ecology and interactions with humans

Climate change poses a pervasive threat to humans and wildlife by altering resource availability, changing co-occurrences, and directly or indirectly influencing human-wildlife interactions. For many wildlife agencies in North America, managing bears ( Ursus spp.) and human-bear interactions is a priority, yet the direct and indirect effects of climate change are exacerbating management challenges. Understanding the underlying ecological drivers of bear responses to climate variability and change, and the implications for conflict, will be critical for maintaining human-bear coexistence in North America. We synthesized 120 articles that identified direct and indirect mechanisms by which climate variability and change affect brown bears ( Ursus arctos ) and American black bears ( Ursus americanus ) in North America. The literature focused on examining climate impacts on bear diet, body size, habitat selection, space use, activity, denning chronology, and population demographics and dynamics. Across these categories, we summarized the documented and projected bear responses and resulting implications for human-bear interactions. Climate-driven changes in natural food availability were frequently implicated in influencing bear behavior and demography, and creating conditions under which interactions with humans are likely to increase. Bears in North America may face increased challenges as habitat and natural food availability continue to be altered by climate change. Our review provides a foundation upon which to identify climate drivers of bear ecology, conditions conducive to human-bear interactions, and adaptive management strategies. Given substantial evidence of climate impacts to bears, incorporating climate considerations into bear management can help managers strategically allocate resources and promote human-bear coexistence.

Biological Conservation↗
USGS2020

Individual and population fitness consequences associated with large carnivore use of residential development

Large carnivores are negotiating increasingly developed landscapes, but little is known about how such behavioral plasticity influences their demographic rates and population trends. Some investigators have suggested that the ability of carnivores to behaviorally adapt to human development will enable their persistence, and yet, others have suggested that such landscapes are likely to serve as population sinks or ecological traps. To understand how plasticity in black bear (Ursus americanus) use of residential development influences their population dynamics, we conducted a 6 year study near Durango, Colorado, USA. Using space-use data on individual bears, we examined the influence of use of residential development on annual measures of bear body fat, cub productivity, cub survival and adult female survival, after accounting for variation in natural food availability and individual attributes (e.g., age). We then used our field-based vital rate estimates to parameterize a matrix model that simulated asymptotic population growth for bears using residential development to different degrees. We found that bear use of residential development was highly variable within and across years, with bears increasing their foraging within development when natural foods were scarce. Increased bear use of development was associated with increased body fat and cub productivity, but reduced cub and adult survival. When these effects were simultaneously incorporated into a matrix model we found that the population was projected to decline as bear use of development increased, given that the costs of reduced survival outweighed the benefits of enhanced productivity. Our results provide a mechanistic understanding of how black bear use of residential development exerts opposing effects on different bear fitness traits and a negative effect on population growth, with the magnitude of those effects mediated by variation in environmental conditions. They also highlight the importance of monitoring bear population dynamics, particularly as shifts in bear behavior are likely to drive increases in human-bear conflicts and the perception of growing bear populations. Finally, our work emphasizes the need to consider the demographic viability of large carnivore populations when promoting the coexistence of people and carnivores on shared landscapes.

Colorado↗
USGS2024

From causes of conflict to solutions: Shifting the lens on human–carnivore coexistence research

Human-carnivore conflicts pose significant challenges in the management and conservation of carnivores across the globe. Abundant research has led to generalizable insights into the causes of such conflicts. For example, conflicts predictably occur when carnivores have access to human food resources, particularly when their natural foods are scarce. However, similar insights into the effectiveness of interventions aimed at coexistence remains comparatively scarce. We hypothesized that this disparity might be reflected in a bias toward research focused on causes of conflict rather than interventions to address it. To test our hypothesis, we evaluated the content of studies on human–carnivore conflicts and coexistence in Canada and the United States from 2010 to 2021. We found that studies disproportionately focused on causes of conflict, with that discrepancy increasing through our study period. We also found a disproportionate focus on black bears and wolves and western jurisdictions, and a disproportionate use of observational (vs. experimental) approaches. Studies on conflict interventions were primarily directed at the carnivores themselves (e.g., lethal approaches) versus human elements (e.g., attractant management, policies), despite evidence that the latter are more effective. We expect that a shift in focus toward solutions-oriented research, integrating insights across geographies, taxa, social contexts, and disciplines, would facilitate effective interventions and foster coexistence, improving outcomes for people and carnivores alike.

Conservation Science and Practice↗
USGS2018

Winter feeding of elk in the Greater Yellowstone Ecosystem and its effects on disease dynamics

Providing food to wildlife during periods when natural food is limited results in aggregations that may facilitate disease transmission. This is exemplified in western Wyoming where institutional feeding over the past century has aimed to mitigate wildlife–livestock conflict and minimize winter mortality of elk ( Cervus canadensis ). Here we review research across 23 winter feedgrounds where the most studied disease is brucellosis, caused by the bacterium Brucella abortus . Traditional veterinary practices (vaccination, test-and-slaughter) have thus far been unable to control this disease in elk, which can spill over to cattle. Current disease-reduction efforts are being guided by ecological research on elk movement and density, reproduction, stress, co-infections and scavengers. Given the right tools, feedgrounds could provide opportunities for adaptive management of brucellosis through regular animal testing and population-level manipulations. Our analyses of several such manipulations highlight the value of a research–management partnership guided by hypothesis testing, despite the constraints of the sociopolitical environment. However, brucellosis is now spreading in unfed elk herds, while other diseases (e.g. chronic wasting disease) are of increasing concern at feedgrounds. Therefore experimental closures of feedgrounds, reduced feeding and lower elk populations merit consideration.

Wyoming↗
USGS1979

Relating residue in raccoon feces to food consumed

Feeding tests were conducted with captive raccoons ( Procyon lotor ) to permit more meaningful interpretation of food habit data obtained from fecal analysis. Ten diverse types of natural foods were offered in 20 tests. Digestibility coefficients were calculated that ranged from 3.6 for dry sunflowers, where considerable residue was recovered, to infinity for earthworms and boned meat where no residue was recovered. The influence of differences in both food and animal behavior on digestibility coefficients was significant (ANOVA, F<0.001). The use of digestibility coefficients to adjust quantitative estimates of fecal residue or to predict biomass consumed is of questionable value with raccoons due to variability in foods consumed and behavior of individual animals.

American Midland Naturalist↗
USGS1983

Seasonal energetics and behavior of captive canvasbacks (Aythia valisineria)

Dramatic changes in the food habits and distribution of Chesapeake Bay canvasbacks (Aythya valisineria) generated a desire to better understand the energetics and behavior of this species on its wintering grounds. Captive canvasbacks were maintained ad libitum on 5 diets during the winters of 1978-80 to evaluate varying protein and energy levels in the diets. Food consumption, weight, blood, and behavior were variables measured to assess affect of diet. Food consumption was higher (P<0.05) for canvasbacks on the low energy (1543 kcal/kg) diets than birds on the high energy (3638 kcal/kg) diets, but body weights did not differ (P<0.05) between diets for males or females. Food consumption and body weights were greatest in November and April and least in January and February. Canvas backs lost weight and ate less during the most stressful periods in spite of adequate food supplies. Blood parameters and behavior of captive canvasbacks did not differ between diets, although differences (P<0.05) were detected for some blood parameters and behaviors between sexes, ages, and seasons. Canvasbacks were more inactive during the coldest months. Changes in behavior, weight, and food consumption appear to be a mechanism to conserve energy at a time when natural food supplies are less plentiful or less available. Aquatic vegetation has declined in quantity making canvasbacks more dependent on invertebrates. Availability of low energy food (e.g. clams) may be the limiting factor in regard to the winter survival of wild canvasbacks.

Poultry Science↗
USGS2012

Stable isotopes to detect food-conditioned bears and to evaluate human-bear management

We used genetic and stable isotope analysis of hair from free-ranging black bears (Ursus americanus) in Yosemite National Park, California, USA to: 1) identify bears that consume human food, 2) estimate the diets of these bears, and 3) evaluate the Yosemite human–bear management program. Specifically, we analyzed the isotopic composition of hair from bears known a priori to be food-conditioned or non-food-conditioned and used these data to predict whether bears with an unknown management status were food-conditioned (FC) or non-food-conditioned (NFC). We used a stable isotope mixing model to estimate the proportional contribution of natural foods (plants and animals) versus human food in the diets of FC bears. We then used results from both analyses to evaluate proactive (population-level) and reactive (individual-level) human–bear management, and discussed new metrics to evaluate the overall human–bear management program in Yosemite. Our results indicated that 19 out of 145 (13%) unknown bears sampled from 2005 to 2007 were food-conditioned. The proportion of human food in the diets of known FC bears likely declined from 2001–2003 to 2005–2007, suggesting proactive management was successful in reducing the amount of human food available to bears. In contrast, reactive management was not successful in changing the management status of known FC bears to NFC bears, or in reducing the contribution of human food to the diets of FC bears. Nine known FC bears were recaptured on 14 occasions from 2001 to 2007; all bears were classified as FC during subsequent recaptures, and human–bear management did not reduce the amount of human food in the diets of FC bears. Based on our results, we suggest Yosemite continue implementing proactive human–bear management, reevaluate reactive management, and consider removing problem bears (those involved in repeated bear incidents) from the population.

California↗
USGS2010

Reproduction in mallards exposed to dietary concentrations of methylmercury

The purpose of this experiment was to use mallards ( Anas platyrhynchos ) tested under controlled conditions to determine how much harm to reproduction resulted from various concentrations of mercury in eggs. Breeding pairs of mallards were fed a control diet or diets containing 1, 2, 4, or 8 μg/g mercury, as methylmercury chloride. Mean concentrations of mercury in eggs laid by parents fed 0, 1, 2, 4, or 8 μg/g mercury were 0.0, 1.6, 3.7, 5.9, and 14 μg/g mercury on a wet-weight basis. There were no signs of mercury poisoning in the adults, and fertility and hatching success of eggs were not affected by mercury. Survival of ducklings and the number of ducklings produced per female were reduced by the 4 and 8-μg/g dietary mercury treatments (that resulted in 5.9 and 14 μg/g mercury in their eggs, respectively). Ducklings from parents fed the various mercury diets were just as heavy as controls at hatching, but by 6 days of age ducklings whose parents had been fed 4 or 8 μg/g mercury weighed less than controls. Because we do not know if absorption of mercury from our diets would be the same as absorption from natural foods, the mercury concentrations we report in eggs may be more useful in extrapolating to possible harmful effects in nature than are the dietary levels we fed. We conclude that mallard reproduction does not appear to be particularly sensitive to methylmercury.

Ecotoxicology↗
USGS2015

Spatial complexity reduces interaction strengths in the meta-food web of a river floodplain mosaic

Theory states that both the spatial complexity of landscapes and the strength of interactions between consumers and their resources are important for maintaining biodiversity and the 'balance of nature.' Spatial complexity is hypothesized to promote biodiversity by reducing potential for competitive exclusion; whereas, models show weak trophic interactions can enhance stability and maintain biodiversity by dampening destabilizing oscillations associated with strong interactions. Here we show that spatial complexity can reduce the strength of consumer-resource interactions in natural food webs. By sequentially aggregating food webs of individual aquatic habitat patches across a floodplain mosaic, we found that increasing spatial complexity resulted in decreases in the strength of interactions between predators and prey, owing to a greater proportion of weak interactions and a reduced proportion of strong interactions in the meta-food web. The main mechanism behind this pattern was that some patches provided predation refugia for species which were often strongly preyed upon in other patches. If weak trophic interactions do indeed promote stability, then our findings may signal an additional mechanism by which complexity and stability are linked in nature. In turn, this may have implications for how the values of landscape complexity, and the costs of biophysical homogenization, are assessed.

Ecology↗
USGS1980

Food use and nutrition of black ducks nesting in Maine

Based on 32 adult black ducks ( Anas rubripes ) collected during the nesting seasons of 1974-76, the proportion of macro invertebrates (as aggregate [average] percent of dry weight) in the diet of males, egg-laying females, and postlaying females was 60, 75, and 55%, respectivey. Sample sizes were small, and the differences associated with sex and reproductive condition were not signficant. Molluscs, Isopods, ephemeropteran and odonate nymphs, and coleopteran, trichopteran, and dipteran larvae contributed 74% of the dry weight and 64% of the gross energy ingested. Data from proximate analyses of 9 invertebrate and 9 plant foods were combined with food habits data to estimate the nutrients available to breeding hens. We concluded that females with access to an adequate amount of natural food including invertebrates and the seeds and tubers of aquatic plants would obtain sufficient minerals, protein, and energy for reproduction. Food quality does not appear to limit the density of black ducks nesting in Maine.

Maine↗
USGS2000

Releasing captive-reared masked bobwhite for population recovery: A review

Efforts to re-establish the endangered masked bobwhite (Colinus virginianus ridgwayi) to it's former southern Arizona range have been ongoing since establishment of the Buenos Aires National Wildlife Refuge in 1986. Pre-release conditioning techniques developed prior to Refuge establishment continued to be utilized in an effort to improve post-release survival of captive-reared masked bobwhite chicks. Foremost among these techniques was the use of wild Texas bobwhite (C. v. texanus) males as foster parents which were paired with all broods released on the Refuge. The efficacy of this technique was evaluated using radio telemetry in 1994, and the results indicated that the use of foster Texas males was not as effective as had been presumed because post-release chick survival was poor. Therefore, in 1995 pre-release conditioning protocol were modified in an effort to improve post-release survival. The primary intent of these modifications was to emphasize wild behavior among chicks prior to release. Modifications to established protocol included imprinting chicks to adult bobwhites immediately after eggs hatched and exposing 1-to-2 day old chicks to natural foods (insects and seeds) while they were in brooder units. Foster parents and their respective broods were then placed in flight pens that mimicked the natural conditions that would confront broods upon release. Family groups were held in flight pens for several weeks for acclimatization purposes and then transported to temporary enclosures erected at release sites where they were held for a week and then released. Finally all releases were conducted during fall after covey formation was apparent to ensure that foster parents and released chicks remained with a group of birds. Preliminary results indicated that post-release chick survival was higher than what was observed in 1994. Pre-conditioning research will continue in an effort to further quantify post-release survival of masked bobwhite chicks. Although the results of this research project are preliminary, it is possible that pre-release conditioning techniques developed for masked bobwhites will prove useful to quail reestablishment efforts throughout North America.

Book chapter↗
USGS2013

Effects of food availability on yolk androgen deposition in the black-legged kittiwake (Rissa tridactyla), a seabird with facultative brood reduction

In birds with facultative brood reduction, survival of the junior chick is thought to be regulated primarily by food availability. In black-legged kittiwakes ( Rissa tridactyla ) where parents and chicks are provided with unlimited access to supplemental food during the breeding season, brood reduction still occurs and varies interannually. Survival of the junior chick is therefore affected by factors in addition to the amount of food directly available to them. Maternally deposited yolk androgens affect competitive dynamics within a brood, and may be one of the mechanisms by which mothers mediate brood reduction in response to a suite of environmental and physiological cues. The goal of this study was to determine whether food supplementation during the pre-lay period affected patterns of yolk androgen deposition in free-living kittiwakes in two years (2003 and 2004) that varied in natural food availability. Chick survival was measured concurrently in other nests where eggs were not collected. In both years, supplemental feeding increased female investment in eggs by increasing egg mass. First-laid (“A”) eggs were heavier but contained less testosterone and androstenedione than second-laid (“B”) eggs across years and treatments. Yolk testosterone was higher in 2003 (the year with higher B chick survival) across treatments. The difference in yolk testosterone levels between eggs within a clutch varied among years and treatments such that it was relatively small when B chick experienced the lowest and the highest survival probabilities, and increased with intermediate B chick survival probabilities. The magnitude of testosterone asymmetry in a clutch may allow females to optimize fitness by either predisposing a brood for reduction or facilitating survival of younger chicks.

Alaska↗
USGS1988

Nutritional values of waterfowl foods

wetland habitats throughout their annual cycles. Survival, reproduction, and growth are dependent on the availability of foods that meet nutritional requirements for recurring biological events. These requirements occur among a wide variety of environmental conditions that also influence nutritional demands. Recent work on nesting waterfowl has identified the female’s general nutrient needs for egg laying and incubation. Far less is known about nutritional requirements for molt and other portions of the life cycle, particularly those during the nonbreeding season. Although information on specific requirements for amino acids and micronutrients of wild birds is meager, the available information on waterfowl requirements can be used to develop waterfowl management strategies. For example, nutrient content of foods, nutritional requirements of waterfowl, and the cues waterfowl use in locating and selecting foods are all kinds of information that managers need to encourage use of habitats by feeding waterfowl. Waterfowl nutritional needs during the annual cycle and the nutritional values of natural foods and crops will be discussed below.

Fish and Wildlife Leaflet↗
USGS2012

Stable isotopes identify dietary changes associated with beak deformities in Black-Capped Chickadees ( Poecile atricapillus )

A large number of beak deformities of unknown etiology have recently been reported in Black-capped Chickadees (Poecile atricapillus) and other resident avian species in Alaska. We investigated the potential association between diet and beak deformities. We analyzed carbon (δ13C) and nitrogen (δ15N) isotopes in whole blood of Black-capped Chickadees captured at three semiurban sites in south-central Alaska. For dietary analysis, we included natural foods (arthropods, seeds, and berries) and anthropogenic items commonly provided in bird feeders (sunflower seeds, peanut butter, and suet). Blood samples from individuals with beak deformities exhibited lower δ15N values and more variable δ13C values than birds with normal beaks. Isotopic values of blood also differed by location for both carbon and nitrogen, but we did not detect a difference in natural dietary items across the three sites. Contributions of individual diet items differed between birds with and without beak deformities, a pattern that likely reflected reduced function of the beak. Affected birds generally consumed fewer arthropods and sunflower seeds and more peanut butter and natural seeds and berries. Although some individuals with beak deformities relied heavily on feeder foods, we did not find evidence of an anthropogenic food source shared by all affected birds. In addition, dietary differences were most pronounced for moderately to severely affected birds, which suggests that these differences are more likely to be a consequence than a cause of deformities.

Alaska↗
USGS2022

Tooth wear and the apparent consumption of human foods among American black bears (Ursus americanus) in Great Smoky Mountains National Park, USA

Stable isotope analyses of hair have been used to estimate the consumption of human foods by American black bears ( Ursus americanus ). Consumption of human foods influences body mass and reproductive success of bears. However, the underlying factors that cause some bears to become conflict bears and resort to consuming human foods as a portion of their diet are not fully understood. We collected hair samples for stable isotope analysis from 51 black bears in Great Smoky Mountains National Park, Tennessee, USA in 2006. We used δ 13 C values of hairs to determine if the bears were consuming C 3 -based (natural foods) or C 4 -based (human foods) diets, and δ 15 N values, which increase with more meat in the diet, as a further indication of the consumption of human foods. Male bears with the heaviest tooth wear had a combination of higher δ 15 N and δ 13 C values, suggesting that they consume human foods to a greater extent than do other black bears. Based on our results, we hypothesize that tooth wear, and thus dental health, may play a role in the consumption of human foods by larger, male bears.

Tennessee↗