Temporal variability in winter travel patterns of Yellowstone bison: the effects of road grooming.

The influence of winter recreation on wildlife in Yellowstone National Park (YNP), Wyoming and Montana, USA, is a controversial issue. In particular, the effects of road grooming, done to facilitate snowmobile and snowcoach travel, on bison (Bison bison) ecology are under debate. We collected data during winters, from 1997 to 2005, on bison road use, off-road travel, and activity budgets to quantify temporal trends in the amount of bison road and off-road travel and to identify the ecological factors affecting bison movements and use of the groomed road system in the Madison-Gibbon-Firehole (MGF) area of YNP. Using model comparison techniques, we found bison travel patterns to be influenced by multiple, interacting effects. Road travel was negatively correlated with road grooming, and we found no evidence that bison preferentially used groomed roads during winter. Snow water equivalent, bison density, and the springtime melt period were positively correlated with both bison road and off-road travel. From behavioral scans on 68,791 bison, we found that travel is only a small percentage (11%) of all bison activity, with foraging comprising 67% of observations. Also, only 7% of traveling bison and 30% of foraging bison were displacing snow, and we suggest foraging, rather than traveling, is likely the major energetic cost to bison in winter. Bison utilize their own trail network, connecting foraging areas using stream corridors, geothermal pathways, and self-groomed travel routes. Our results indicate that temporal patterns in bison road travel are a manifestation of general travel behavior and that groomed roads in the MGF do not appear to be a major factor influencing bison ecology and spatial redistribution. We suggest that the changes in bison spatial dynamics during the past three decades have likely been the result of the natural phenomenon of density-dependent range expansion, rather than having been caused by the anthropogenic influence of road grooming.     

Covariates affecting spatial variability in bison travel behavior in Yellowstone National Park.

Understanding mechanisms influencing the movement paths of animals is essential for comprehending behavior and accurately predicting use of travel corridors. In Yellowstone National Park (USA), the effects of roads and winter road grooming on bison (Bison bison) travel routes and spatial dynamics have been debated for more than a decade. However, no rigorous studies have been conducted on bison spatial movement patterns. We collected 121 380 locations from 14 female bison with GPS collars in central Yellowstone to examine how topography, habitat type, roads, and elevation affected the probability of bison travel year-round. We also conducted daily winter bison road use surveys (2003-2005) to quantify how topography and habitat type influenced spatial variability in the amount of bison road travel. Using model comparison techniques, we found the probability of bison travel and spatial distribution of travel locations were affected by multiple topographic and habitat type attributes including slope, landscape roughness, habitat type, elevation, and distances to streams, foraging areas, forested habitats, and roads. Streams were the most influential natural landscape feature affecting bison travel, and results suggest the bison travel network throughout central Yellowstone is spatially defined largely by the presence of streams that connect foraging areas. Also, the probability of bison travel was higher in regions of variable topography that constrain movements, such as in canyons. Pronounced travel corridors existed both in close association with roads and distant from any roads, and results indicate that roads may facilitate bison travel in certain areas. However, our findings suggest that many road segments used as travel corridors are overlaid upon natural travel pathways because road segments receiving high amounts of bison travel had similar landscape features as natural travel corridors. We suggest that most spatial patterns in bison road travel are a manifestation of general spatial travel trends. Our research offers novel insights into bison spatial dynamics and provides conceptual and analytical frameworks for examining movement patterns of other species.     

On the Origin of Brucellosis in Bison of Yellowstone National Park: A Review

Brucellosis caused by Brucella abortus occurs in the free-ranging bison ( Bison bison ) of Yellowstone and Wood Buffalo National Parks and in elk ( Cervus elaphus ) of the Greater Yellowstone Area. As a result of nationwide bovine brucellosis eradication programs, states and provinces proximate to the national parks are considered free of bovine brucellosis. Thus, increased attention has been focused on the wildlife within these areas as potential reservoirs for transmission to cattle. Because the national parks are mandated as natural areas, the question has been raised as to whether Brucella abortus is endogenous or exogenous to bison, particularly for Yellowstone National Park. We synthesized diverse lines of inquiry, including the evolutionary history of both bison and Brucella , wild animals as Brucella hosts, biochemical and genetic information, behavioral characteristics of host and organism, and area history to develop an evaluation of the question for the National Park Service. All lines of inquiry indicated that the organism was introduced to North America with cattle, and that the introduction into the Yellowstone bison probably was directly from cattle shortly before 1917. Fistulous withers of horses was a less likely possibility. Elk on winter feedgrounds south of Yellowstone National Park apparently acquired the disease directly from cattle. Bison presently using Grand Teton National Park probably acquired brucellosis from feedground elk.     

Cover Caption

Cover: During winter in the interior of Yellowstone National Park most elk migrate from deep snow while many bison do not, existing near thermal areas and on wind-blown ridges. Wolves still attempt to kill these bison and often spend hours making a kill. Wolf-bison systems used to dominate in North America prior to European settlement but now only Yellowstone and Wood Buffalo National Parks have intact wolf-bison systems. See pp. 1105-1116. Photo by Doug Smith, National Park Service.     

Group size and foraging efficiency in yellow baboons

Summary I studied the foraging behaviour of adults in three different-sized groups of yellow baboons (Papio cynocephalus) at Amboseli National Park in Kenya to assess the relationship between group size and foraging efficiency in this species. Study groups ranged in size from 8 to 44 members; within each group, I collected feeding data for the dominant adult male, the highest ranking pregnant female, and the highest ranking female with a young infant. There were no significant differences between groups during the study in either the mean estimated energy value of the food ingested per day for each individual (385±27 kJ kg^-1 day^-1) or in the estimated energy expended to obtain that food (114±3 kJ kg^-1 day^-1). Mean foraging efficiency ratios, which reflect net energy gain per unit of foraging time, also did not vary as a function of the size of the group in which the baboons were living. There was substantial variation between days in the efficiency ratios of all animals; this was the result of large differences in energy intake rather than in the energy expended during foraging itself. The members of the smallest group spent on the average only one-half as much time feeding each day as did individuals in the two larger groups. However, they obtained almost as much energy while foraging, primarily because their rate of food intake while actually eating tended to be higher than the rate in the other groups. The baboons in the small group were observed closer to trees that they could climb to escape ground predators, and they also were more likely to sit in locations elevated above the ground while resting. Such differences would be expected if the members of the small group were less able to detect approaching predators than individuals that lived in the larger groups. The results of this study suggest that predator detection or avoidance, rather than increased foraging efficiency, may be the primary benefit of living in larger groups in this population.     

Wildlife Disease in U.S. National Parks: Historical and Coevolutionary Perspectives

Diseases of wildlife have significant management implications in a number of lands of the U.S. National Park Service due to increasing interactions between wildlife and domestic animals. We review the paleontology, history, and coevolution of infectious diseases in North American ungulates. We provide two examples related to bovine brucellosis in bison in Yellowstone National Park and lungworm-pneumonia complex in bighorn sheep in several western national parks. These examples illustrate the difficulty of managing wild populations and their diseases in national parks and other protected areas. In some instances, human intervention may be justifiable in order to protect native populations, domestic animals, and humans from acquiring a disease.     

Searching behavior and use of sampling information by free-ranging bison (Bos bison)

I examined the searching behavior of free-ranging plains bison (Bos bison bison) in their natural habitat, and determined whether their assessment of food patch quality was influenced by the short-term sampling information acquired during search. Bison used area-concentrated search during their winter foraging activity. Their movements between areas of suitable food patches were influenced by local environmental conditions, being sometimes less sinuous, and at other times more sinuous, than expected from a correlated random walk model. Bison also systematically avoided digging in areas where plants of low profitability lay under the snow. Where they dug, there was evidence that a bison's perception of food quality varied during a foraging bout, and was therefore influenced by short-term sampling information. After controlling for forage quality, I found that small feeding craters were more likely to be preceded by samples of high quality food patches. My observations suggest that bison take advantage of the structural characteristics of their environment during searching activity, and base foraging decisions on local rather than global availability.     

Assessment of prey vulnerability through analysis of wolf movements and kill sites.

Within predator-prey systems behavior can heavily influence spatial dynamics, and accordingly, the theoretical study of how spatial dynamics relate to stability within these systems has a rich history. However, our understanding of these behaviors in large mammalian systems is poorly developed. To address the relationship between predator selection patterns, prey density, and prey vulnerability, we quantified selection patterns for two fine-scale behaviors of a recovering wolf (Canis lupus) population in Yellowstone National Park, Wyoming, USA. Wolf spatial data were collected between November and May from 1998-1999 until 2001-2002. Over four winters, 244 aerial locations, 522 ground-based telemetry locations, 1287 km of movement data from snow tracking, and the locations of 279 wolf kill sites were recorded. There was evidence that elk (Cervus elaphus) and bison (Bison bison) densities had a weak effect on the sites where wolves traveled and made kills. Wolf movements showed a strong selection for geothermal areas, meadows, and areas near various types of habitat edges. Proximity to edge and habitat class also had a strong influence on the locations where elk were most vulnerable to predation. There was little evidence that wolf kill sites differed from the places where wolves traveled, indicating that elk vulnerability influenced where wolves selected to travel. Our results indicate that elk are more vulnerable to wolves under certain conditions and that wolves are capable of selecting for these conditions. As such, vulnerability plays a central role in predator-prey behavioral games and can potentially impact the systems to which they relate.     

Towards an ecological solution to the folivore paradox: patch depletion as an indicator of within-group scramble competition in red colobus monkeys (Piliocolobus tephrosceles)

A number of socioecological models assume that within-group food competition is either weak or absent among folivorous primates. This assumption is made because their food resources are presumed to be superabundant and evenly dispersed. However, recent evidence increasingly suggests that folivore group size is food-limited, that the primates prefer patchily distributed high-quality foods, and display some of the expected responses to within-group scramble competition. To investigate this apparent contradiction between theoretical models and recent empirical data, we examined the foraging behaviour of red colobus monkeys (Piliocolobus tephrosceles) in Kibale National Park, Uganda. We found that red colobus monkeys foraged in a manner that suggests they deplete patches of preferred foods: intake rate slowed significantly during patch occupancy while movement rate, an index of foraging effort, increased. Furthermore, patch occupancy was related to the size of the feeding group and the size of the patch. These results suggest that within-group scramble competition occurs, may limit folivore group size, and should be considered in models of folivore behavioural ecology.     

Why don't bull moose eat during the rut?

Summary Reduced forage intake by males is generally believed to coincide with the peak of rutting activities in many ungulates. Activity budgets of bull moose (Alces alces) in Denali National Park and Preserve (DNPP) and Isle Royale National Park (IRNP) were analyzed to assess: (1) if time spent foraging decreased during the rut; (2) the timing of reduced forage intake; (3) whether there was variation in feeding time among bulls of varying size; and (4) the proximate mechanism and adaptive value of reduced forage intake. Time spent feeding by bull moose began to decrease around 1 September: large bulls completely ceased feeding for approximately 2 weeks, with median dates of feeding cessation at 18 and 20 September for IRNP and DNPP, respectively. Small bulls fed at reduced rates, but did not cease feeding. Although large bulls in both study sites spent large amounts of time engaged in social behavior during the period of appetite suppression, much of their active time was also spent standing inattentive, i.e., engaged in no activity (45.5% in IRNP, 29.8% in DNPP), suggesting that a constraint in time budgets did not limit opportunities to feed. Forage intake reduction is more likely mediated through a physiological mechanism. Feeding cessation did not coincide with the peak of the rut: at DNPP the median date of feeding cessation was significantly earlier than the median date of breeding behavior and fighting. The timing of feeding cessation coincided with that of scent-urination at both study sites, raising the possibility that appetite suppression may be a byproduct of physiological processes associated with chemical communication.     

Founding Lineages and Genic Variability in Plains Bison (Bison bison) from Badlands National Park, South Dakota

Abstract: Starch-gel electrophoresis was used to screen 101 bison from Badlands National Park, South Dakota, for variation at 24 genetic loci. The population was descended from founder groups of about 6 and 3 individuals, separated geographically for a minimum of 64 years. The purpose of this study was (1) to estimate levels of genic variability in this bison population, (2) to assess the extent to which descendents of the two founder groups differ genetically, and (3) to compare the genetic characteristics of the Badlands population with other bison populations. The Badlands herd was found to be polymorphic for only a single locus (MDH–1). Descendents of the founder groups were homogeneous with respect to allelic and genotypic frequencies at this locus. The MDH–1 polymorphism has not been observed in other bison populations, while several polymorphism reported in other bison populations were not detected in the Badlands herd. A mean heterozygosity of 0.012 was observed in the Badlands herd; this value is lower than that typically reported for mammals, though not as low as heterozygosities seen in other populations that have passed through severe bottlenecks in size. These results underscore the need for genetic data in planning breeding programs for species in captivity or managed in isolate reserves.     

Phenotypic Effects of Cattle Mitochondrial DNA in American Bison

Hybridization between endangered species and more common species is a significant problem in conservation biology because it may result in extinction or loss of adaptation. The historical reduction in abundance and geographic distribution of the American plains bison (Bison bison bison) and their recovery over the last 125 years is well documented. However, introgression from domestic cattle (Bos taurus) into the few remaining bison populations that existed in the late 1800s has now been identified in many modern bison herds. We examined the phenotypic effect of this ancestry by comparing weight and height of bison with cattle or bison mitochondrial DNA (mtDNA) from Santa Catalina Island, California (U.S.A.), a nutritionally stressful environment for bison, and of a group of age‐matched feedlot bison males in Montana, a nutritionally rich environment. The environmental and nutritional differences between these 2 bison populations were very different and demonstrated the phenotypic effect of domestic cattle mtDNA in bison over a broad range of conditions. For example, the average weight of feedlot males that were 2 years of age was 2.54 times greater than that of males from Santa Catalina Island. In both environments, bison with cattle mtDNA had lower weight compared with bison with bison mtDNA, and on Santa Catalina Island, the height of bison with cattle mtDNA was lower than the height of bison with bison mtDNA. These data support the hypothesis that body size is smaller and height is lower in bison with domestic cattle mtDNA and that genomic integrity is important for the conservation of the American plains bison. Efectos Fenotípicos del ADN Mitocondrial de Ganado en el Bisonte Americano     

Ecological constraints on group size: an analysis of spider monkey and chimpanzee subgroups

The social organization of spider monkeys (Ateles geoffroyi) and chimpanzees (Pan troglodytes) appear remarkably similar. In this paper, field studies of these two species were used to (1) test a model of ecological constraints on animal group size which suggests that group size is a function of travel costs and (2) assess ecological and social factors underlying the social organization of these two species. Spider monkeys were studied over a 6-year period in Santa Rosa National Park, Costa Rica, and chimpanzees were studied for 6 years in Kibale National Park, Uganda. Adults of both species spent their time in small subgroups that frequently changed size and composition. Thus, unlike most primate species, spider monkeys and chimpanzees were not always in a spatially cohesive social group; each individual had the option of associating in subgroups of a different size or composition. Both species relied on ripe fruit from trees that could be depleted through their feeding activity. However, spider monkey food resources tended to occur at higher densities, were more common, less temporally variable, and did not reach the low levels experienced by chimpanzees. Analyses of the relationship between subgroup size and the density and distribution of their food resources suggested that travel costs limit subgroup size. However, these ecological factors did not influence all age/sex classes equally. For example, the number of adult males in a subgroup was a function of food density and travel costs. However, this was not the case for female chimpanzees, suggesting that the benefits of being in a subgroup for females did not exceed the costs, even when ecological conditions appeared to minimize subgroup foraging costs. Therefore, it seems likely that social strategies influenced the relationship between food resource variables and subgroup size.     

Dominance rank differences in the energy intake and expenditure of female Bwindi mountain gorillas

Socioecological models predict that contest competition for clumped foods can lead to higher energy intake and lower energy expenditure for higher-ranking individuals. Here, we examine the relationships between dominance rank and energy intake and expenditure of female mountain gorillas in Bwindi Impenetrable National Park, Uganda (Gorilla beringei beringei). Bwindi gorillas have weak dominance relationships, feed on nonreproductive plant parts throughout the year, and consume fruit when it is seasonally available. We used behavioral observations on one group of gorillas and nutritional analysis of their major food items to calculate energy intake rates and estimated energy expenditure. Using linear mixed models, we found a significant positive relationship between dominance rank and energy intake rates, due to higher-ranking females having faster ingestion rates, rather than consuming foods with higher energy concentrations. Lower-ranking females did not spend significantly more time feeding to compensate for their lower energy intake rates. Lower-ranking females spent significantly more time traveling than higher-ranking females, leading to a negative relationship between dominance rank and energy expenditure. The combined results revealed a significant positive relationship between dominance rank and energy balance. Higher-ranking females did not spend longer feeding on fruit than lower-ranking ones, and the relationship between dominance rank and energy intake rates was not stronger when fruit was available. According to socioecological models, these results suggest that contest competition may be occurring with both fruit and nonreproductive plant parts, which would be consistent with growing evidence that nonreproductive plant parts can be contestable.     

Behavioral responses of bison and elk in Yellowstone to snowmobiles and snow coaches.

Managers of public lands are charged with protecting some of our most important natural resources and ecosystems, while providing for their use and enjoyment by visitors. Almost one million visitors entered Yellowstone National Park by motorized means on snowmobiles (87%) or snow coaches (13%) during 1992-2003. Most vehicles toured the central portion of the park where bison (Bison bison) and elk (Cervus elaphus) concentrate in geothermal areas. We sampled >6500 interactions between groups of these species and groups of snowmobiles and snow coaches (collectively, OSV, over-snow vehicles) during five winters (1999-2000, 2002-2004). Multinomial logits models were used to identify conditions leading to behavioral responses. Elk responded three times as often (52%) as bison (19%) during interactions with groups of snowmobiles and snow coaches due to increased vigilance responses (elk, 44%; bison, 10%). However, the frequency of higher-intensity movement responses by bison and elk were similar (6-7% travel, 1-2% flight, <1% defense) and relatively low compared to other studies of ungulates and snowmobile disturbance. The likelihood of active responses by bison and elk increased significantly if animals were on or near roads, groups were smaller, or humans approached. The likelihood of an active response by bison decreased within winters having the largest visitation, suggesting some habituation to snowmobiles and snow coaches. There was no evidence that snowmobile use during the past 35 years affected the population dynamics or demography of bison or elk. Thus, we suggest that regulations restricting levels and travel routes of over-snow vehicles (OSVs) were effective at reducing disturbances to bison and elk below a level that would cause measurable fitness effects. We recommend park managers consider maintaining OSV traffic levels at or below those observed during our study. Regardless, differing interpretations of the behavioral and physiological response data will continue to exist because of the diverse values and beliefs of the many constituencies of Yellowstone.     

Optimal movement strategies for social foragers in unpredictable environments

Spatial movement models often base movement decision rules on traditional optimal foraging theories, including ideal free distribution (IFD) theory, more recently generalized as density-dependent habitat selection (DDHS) theory, and the marginal value theorem (MVT). Thus optimal patch departure times are predicted on the basis of the density-dependent resource level in the patch. Recently, alternatives to density as a habitat selection criterion, such as individual knowledge of the resource distribution, conspecific attraction, and site fidelity, have been recognized as important influences on movement behavior in environments with an uncertain resource distribution. For foraging processes incorporating these influences, it is not clear whether simple optimal foraging theories provide a reasonable approximation to animal behavior or whether they may be misleading. This study compares patch departure strategies predicted by DDHS theory and the MVT with evolutionarily optimal patch departure strategies for a wide range of foraging scenarios. The level of accuracy with which individuals can navigate toward local food sources is varied, and individual tendency for conspecific attraction or repulsion is optimized over a continuous spectrum. We find that DDHS theory and the MVT accurately predict the evolutionarily optimal patch departure strategy for foragers with high navigational accuracy for a wide range of resource distributions. As navigational accuracy is reduced, the patch departure strategy cannot be accurately predicted by these theories for environments with a heterogeneous resource distribution. In these situations, social forces improve foraging success and have a strong influence on optimal patch departure strategies, causing individuals to stay longer in patches than the optimal foraging theories predict.     

Integrated modelling of foraging behaviour, energy budget and memory properties

A predator's foraging performance is related to its ability to acquire sufficient information on environmental profitability. This process can be affected by the patchy distribution and clustering of food resources and by the food intake process dynamics.We simulated body mass growth and behaviour in a forager acting in a patchy environment with patchy distribution of both prey abundance and body mass by an individual-based model. In our model, food intake was a discrete and stochastic process and leaving decision was based on the estimate of net energy gain and searching time during their foraging activities. The study aimed to investigate the effects of learning processes and food resource exploitation on body mass and survival of foragers under different scenarios of intra-patch resource distribution.The simulation output showed that different sources of resource variability between patches affected foraging efficiency differently. When prey abundance varied across patches, the predator stayed longer in poorest patches to obtain the information needed and its performance was affected by the cost of sampling and the resulting assessment of the environment proved unreliable. On the other hand, when prey body mass, but not abundance, varied among the patches the predator was quickly able to assess local profitability. Both body mass and survival of the predator were greatly affected by learning processes and patterns of food resource distribution.     

Colony energy requirements affect the foraging currency of bumble bees

Summary This study examines whether the foraging behavior of worker bumble bees (Bombus: Apidae) collecting nectar on inflorescences of seablush (Plectritis congesta: Valerianaceae) is affected by colony energetic requirements, which were experimentally manipulated either by adding sucrose solution to honey pots or by removing virtually all available nectar from the pots. The competing hypotheses tested were: (1) no change; energetic requirements do not affect behavior, since there is a single best way to collect food in a given environment; (2) energetic currency; the energetic currency maximized by foragers changes according to colony energetic condition, with nectar-depletion causing a shift from maximizing long-term productivity to maximizing immediate energetic gain, thereby de-emphasizing energetic costs; and (3) predation; foragers devalue risk of predation as risk of starvation increaes, with colony nectar-depletion causing foragers to be less predation riskaverse in order to increase immediate energetic gain. Relative to when their colony energy reserves were enhanced, foragers from nectar-depleted colonies selected smaller inflorescences, visited fewer flowers per inflorescence, probed flowers at a higher rate while on each inflorescence, and walked between inflorescences less often, thereby spending a greater proportion of their foraging trip in flight. These behaviors increased a bee's energetic costs while foraging, and should also have increased its immediate energetic gains, allowing rejection of the no change hypothesis. Predictions of the predation hypothesis were generally not supported, and our results best support the energetic currency hypothesis. Foraging currency of bumble bees therefore appears to be a function of colony energetic state. Offprint requests to: R.V. Cartar     

A geometrical model for the effect of interference on food intake

Interference competition is often due to kleptoparasitism (food stealing). In which case, the attack distance, the distance over which one animal attacks another in an attempt to steal food, determines to a large extent the competitor density range over which interference significantly affects the intake rate of foraging animals.We develop a simple model of kleptoparasitism containing three parameters: attack distance, the density of foraging animals and a single dimensionless parameter α which summarizes the non-geometrical aspects of the interference process. Dominant and subdominant animals are not considered separately. The model predicts that the average intake rate will decrease exponentially with animal density and that a measure of the strength of interference depends on attack distance squared.The simple model is compared with a much more detailed individual-based foraging model from the literature. Simulated average intake rates are indeed well approximated by an exponential decrease with competitor density. Also the measure of interference behaves in the way expected from the simple model. By explaining the shape of the relationship between intake rate and animal density, the simple model provides insight into the behaviour of the detailed behavioural model.Insight into the role of geometry is important in the interpretation of field results and in the further development of detailed foraging models.     

Dominance and the dynamics of phenotype-limited distribution in common cranes

We studied the behavior of 13 radiotagged cranes dispersing from a communal roost over days when they changed their main daily foraging area between consecutive days during two winter seasons. Individuals went to a new foraging zone when on the previous day their morning food intake had fallen below their mean morning food intake measured over the whole winter. Food intake on the day before a change in foraging area was positively correlated with dominance rank. Dominant cranes changed to new zones with higher numbers of birds and food density, while subordinate cranes went to new zones with lower numbers of birds. As a result, all birds increased their food intake over that of the previous day. Dominant cranes remained more faithful to their most preferred foraging zone, where they spent 69% of the mornings, while subordinate birds were more mobile, switching among zones frequently. Dominant birds left the roost later than subordinate birds on the days they changed to a new zone, which could be used to track the main departing flows. The results suggest that the dynamics that led to a truncated phenotype-limited distribution were determined by social dominance and food abundance, with dominant cranes shifting to a new zone to maintain their high intake levels and subordinates changing more frequently whenever their daily intake did not reach the minimum metabolic requirements. Received: 16 December 1996 / Accepted after revision: 22 February 1997