Apparent Predation Research Articles

Apparent Predation by Rock Wren of Common Sagebrush Lizard

Apparent Predation by Rock Wren of Common Sagebrush Lizard

Parasitoid-mediated indirect interactions between unsuitable and suitable hosts generate apparent predation in microcosm and modeling studies.

Parasitoids used as biological control agents often parasitize more than a single host species and these hosts tend to vary in suitability for offspring development. The population dynamics of parasitoids and hosts may be altered by these interactions, with outcomes dependent on the levels of suitability and acceptance of both host species. Parasitism of individuals of an unsuitable host species may indirectly increase populations of a suitable host species if eggs laid into unsuitable hosts do not develop into adult parasitoids. In this case, the unsuitable host is acting as an egg sink for parasitoids and this can reduce parasitism of suitable hosts under conditions of egg limitation. We studied parasitoid‐mediated indirect interactions between two aphid hosts, Aphis glycines (the soybean aphid) and A. nerii (the milkweed, or oleander aphid), sharing the parasitoid Aphelinus certus. While both of these aphid species are accepted by A. certus, soybean aphid is a much more suitable host than milkweed aphid is. We observed a drastic reduction of parasitoid offspring production (45%) on the suitable host in the presence of the unsuitable host in microcosm assays. Aphelinus certus females laid eggs into the unsuitable hosts (Aphis nerii) in the presence of the suitable host leading to egg and/or time limitation and reduced fitness. The impact of these interactions on the equilibrium population sizes of the three interacting species was analyzed using a consumer–resource modeling approach. Both the results from the laboratory experiment and the modeling approaches identified apparent predation between soybean aphid and milkweed aphid, in which milkweed aphid acts as a sink for parasitoid eggs leading to an increase in the soybean aphid population. The presence of soybean aphids had the opposite effect on milkweed aphid populations as it supported increases in parasitoid abundance and thus reduced the fitness and abundance of this aphid species.

Nest survival, predator assemblage, and patterns of predation at Veery (Catharus fuscescens) nests in a mature forest landscape

Predation is typically the primary cause of nest failure for songbirds, even within unfragmented forested landscapes. In recent years, video cameras have been used to study causes and patterns of nest failure in a variety of habitats and regions. However, surprisingly few video camera studies have been performed in forests of northeastern North America. Over 5 years, we monitored Veery (Catharus fuscescens) nesting success in a mature forest landscape in northeastern Pennsylvania and used video cameras at a subset of nests to identify the predator assemblage and to describe relevant patterns of predation. Overall, we located 289 nests and recorded 67 of these nests with video cameras. Annual nest survival rates varied substantially across years (0.17–0.44) with this variation driven primarily by the dominant source of nest mortality: predation. Video cameras recorded 40 predation events by 12 predator species. Mammals (7 species), birds (4 species), and snakes (1 species) accounted for 75%, 20%, and 2.5% of predation events recorded, respectively. Predation events occurred during the day more often than expected by chance. Logistic exposure analyses indicated that both camera presence and nest age affected nest survival by influencing predation rates, but date did not. The diverse predator community observed depredating Veery nests led to low nesting success in some years, but also demonstrated that causes of nest failure vary by year and cannot be attributed to any single predator species or group. A greater apparent predation rate at nests with cameras likely resulted from a more frequent visitation rate to these nests by researchers compared to those without cameras and suggests a potential bias with artificially decreased nest survival estimates in years in which cameras were used.

Impact of Redox Conditions on Antibiotic Resistance Conjugative Gene Transfer Frequency and Plasmid Fate in Wastewater Ecosystems.

Wastewater is a common pathway for the spread of antibiotic resistance (AR) genes and bacteria into the environment. Biological treatment can mitigate this path, but horizontal gene transfer (HGT) between bacteria also occurs in such processes, although the influence of bioreactor habitat and ecology on HGT frequency is not well understood. Here, we quantified how oxidation-reduction (redox) conditions impact the fate of a Green fluorescent protein (Gfp)-tagged AR plasmid (pRP4-gfp) within an E. coli host (EcoFJ1) in the liquid phase and biofilms in bioreactors. Replicate reactors treating domestic wastewater were operated under stable aerobic (+195 ± 25 mV), anoxic (-15 ± 50 mV), and anaerobic (-195 ± 15 mV) conditions, and flow cytometry and selective plating were used to quantify donor strain, EcoFJ1(pRP4-gfp), and putative transconjugants over time. Plasmid pRP4-gfp-bearing cells disappeared rapidly in aerobic ecosystems (∼2.0 log reduction after 72 h), especially in the liquid phase. In contrast, EcoFJ1(pRP4-gfp) and putative transconjugants persisted much longer in anaerobic biofilms (∼1.0 log reduction, after 72 h). Plasmid transfer frequencies were also higher under anaerobic conditions. In parallel, protozoan abundances were over 20 times higher in aerobic reactors relative to anaerobic reactors, and protozoa numbers significantly inversely correlated with pRP4-gfp signals across all reactors (p < 0.05). Taken together, observed HGT frequency and plasmid retention are impacted by habitat conditions and trophic effects, especially oxygen conditions and apparent predation. New aerobic bioreactor designs are needed, ideally employing passive aeration to save energy, to minimize resistance HGT in biological wastewater treatment processes.

Identification of predation events in wild fish using novel acoustic transmitters

BackgroundAcoustic telemetry is a commonly used tool to gain knowledge about aquatic animal ecology through the study of their movements. In telemetry studies researchers must make inferences regarding the movements and the fates of tagged animals. Until recently, predation has been inferred in telemetry data using a variety of methods including abrupt changes in movement patterns or habitat use. An acoustic telemetry transmitter has been developed to detect predation events of tagged animals, and while they have performed well in controlled laboratory trials, literature regarding the application of these novel transmitters in field settings is limited. The objective of this research was to describe the detection data obtained from field studies using predation tags and propose methods to incorporate this information in decision-making about the fate of tagged animals. We implanted 60 yellow perch (Perca flavescens) with predation transmitters and evaluated their spatial use in a receiver array (34 ha) using a combination of centres of activity, roaming indices, and step length measures to examine detection data.ResultsOver 5 months, 19 apparent predation events were identified by the transmitters. Roaming indices and centres of activity revealed a variety of detection patterns, including instances of altered behaviour before and after predation that matched tag-indentified predation events, dropped tags post-predation, and detections that ceased post-predation indicating the predator might have left the array. Based on the observed patterns, probable predation was inferred for 15 of 19 triggered tags, with unclear fates for four fish.ConclusionsOur study provided a framework to assess the fate of animals tagged with predation transmitters and demonstrate how these tags can contribute to telemetry studies. We showed how detections can be categorized using tag status to compare movement metrics among individuals, provided tools to explore space use surrounding predation events, and synthesized this information to inform uncertainty surrounding tag-identified predation events. Predation tags do not remove all uncertainty about the fate of tagged individuals, but combined with other metrics they increase the likelihood of identifying abnormal movements that could otherwise introduce biased detection histories into studies of small-sized fishes.

Conservation implications of using an imitation carnivore to assess rarely used refuges as critical habitat features in an alpine ungulate.

Understanding relationships between animals and their habitat is a central goal in ecology with important implications for conservation. Misidentified habitat requirements can have serious repercussions because land protection or reintroductions might occur in less than optimal habitat. Studies of resource selection have greatly facilitated an understanding of ecological relationships but can be improved when vital yet infrequently utilized habitat features are more fully described. A critical element for many prey species is escape terrain or some other form of refuge to avoid predation. Mountain goats (Oreamnos americanus) are well known for their use of cliffs to avoid predation, but a survey of the literature revealed at least twelve different approximations of goat escape terrain, ranging from > 25° to > 50° slopes. Here, we seek to (1) enhance estimates of mountain goat escape terrain and antipredator behavior, and (2) highlight the limitations of the assumption that the time an animal spends in an area is proportional to importance. To improve estimates of goat escape terrain, we conducted field work across two years (2014–15) in Glacier National Park, Montana USA and manipulated apparent predation risk by exposing mountain goats to a threatening simulated grizzly bear (Ursus arctos) treatment and a non-threatening ungulate (control) treatment. Mountain goats moved in response to the simulated bear but not in response to the simulated ungulate, with shorter latencies to move for subjects in larger groups and at shorter distances to the simulated threat. Through a used-unused resource selection function we tested 22 landscape variables to describe the use of escape terrain. Proximity to slopes greater than 60° best explained the locations to which mountain goats fled after exposure to the simulated bear, and the average slope of these escape locations was 56.5° (±14.1 S.D.). Our results suggest that mountain goat escape terrain be considered at slopes of 60° as a minimum because our simulated threat did not include pursuit of goats and, thus, slopes of 60° are likely underestimates of actual escape terrain. Additionally, because direct interactions between carnivores and goats seldom occur, serious escape terrain is infrequently used. Past estimates of escape may have miscalculated the slopes which goats select for in response to predation risk. Based on experimental approaches in the wild, we suggest that anti-predator behavior should be included in studies of resource selection when the goal is to consider habitat as a predictor for conservation success. Finally, we discuss evidence suggesting a past mountain goat introduction failed due to lack of adequate escape terrain and subsequent recolonization of a predator.

Non-carnivorous feeding in Arctic chaetognaths

Chaetognaths (arrow worms) are important components of zooplankton communities in terms of abundance, biomass and contribution to carbon export. Though traditionally considered strict carnivores, recent studies have identified “omnivorous” chaetognaths. These may feed on non-animal materials, including algae, detritus or sediments. The feeding strategies of the Arctic species Eukrohnia hamata and Parasagitta elegans are particularly interesting given differences in their vertical distributions, and the strong seasonality (peaks and troughs) in the abundance of expected prey items, such as copepods. We analyse the feeding history of these chaetognaths in the Beaufort and Chukchi Seas, and Baffin Bay, using gut contents (types and colours) as short-term signals (days), and biochemistry (stable isotope, lipid and fatty acid composition) as signals integrated over the longer-term (weeks to months), to investigate seasonality in diets and determine the extent to which animal and non-animal matter are consumed. Between November 2007 and July 2008 in the Beaufort Sea, green detritus and oil droplets were abundant in the guts of only E. hamata and were found to contain evidence of diatoms. Weak differences in apparent predation rates and prey items for the two species, but high amounts of green detritus and silica in E. hamata guts point towards direct ingestion of diatoms and marine snow at both epi- and meso-pelagic depths, and can explain δ15N and δ13C-contents that may predict omnivory in the Chukchi Sea and Baffin Bay (fall 2014). Dietary signals in P. elegans predict that this species has a reduced dependence on diatom source pathways relative to E. hamata, for instance a relative absence in green material in guts, and a lower 16:1 (n − 7) concentration. Whilst nitrogen isotopes and fatty acid biomarkers suggested a more carnivorous diet, they also suggest that Calanus copepods are less important to its diet than other types of zooplankters. We suggest that E. hamata (whether pelagic or hyper-benthic) likely receives a substantial energy input from algae and detritus and is thus not a strict carnivore. Our data provide the stimulus for continued focus on these organisms and the important role they play in carbon flux as we try to better understand carbon cycling in a changing Arctic Ocean.

Predation risk and space use of a declining Dall sheep (Ovis dalli dalli) population.

The abundance of ungulate populations may fluctuate in response to several limiting factors, including climate, diseases, and predation. In the northern Richardson Mountains, Canada, Dall sheep (Ovis dalli dalli) have undergone a major decline in the past decades and predation by grizzly bears (Ursus arctos) and wolves (Canis lupus) was suspected as a leading cause. To better understand the relationship between these three species located in this rugged and remote ecosystem, we relied on a combination of indirect methods. We investigated the apparent role of predation on the Dall sheep population using spatial ecology and stable isotopes. We examined seasonal variation in predation risk, focusing on how it may affect Dall sheep habitat use and sexual segregation, and we evaluated the proportion of Dall sheep in the diet of both predators using stable isotopes. The movements of the three species were monitored by satellite telemetry. Dall sheep habitat use patterns were analyzed using topographical features, greenness index, land cover, and apparent predation risk. The diets of grizzly bears and wolves were examined using a Bayesian mixing model for carbon and nitrogen stable isotopes. We found that Dall sheep habitat use varied seasonally, with different patterns for ewes and rams. Exposure to grizzly bear risk was higher for rams during summer, while ewes were further exposed to wolf apparent predation risk during winter. The importance of safe habitats for ewes was reflected in space use patterns. Stable isotopes analyses suggested that the diet of grizzly bears was largely from animal sources, with mountain mammals comprising about one quarter. Wolves mostly fed on both aquatic browsers and mountain mammals. Diet variation between individual predators suggested that some individuals specialized on mountain mammals, likely including Dall sheep. We conclude that grizzly bear and wolf apparent predation risk are important in driving Dall sheep habitat use and play a role in sexual segregation. Overall, this study presents an innovative combination of indirect methods that could be applied elsewhere to better understand predator-prey dynamics in remote ecosystems.

Effects of forest structure and harvest‐induced edges on predation risk

ABSTRACTManaged forest systems have implications for wildlife conservation because of their direct influence on condition and distribution of forest patches on the landscape. Spatial arrangement, structure, and composition of patches can influence reproductive outcomes for breeding birds by mediating nest site selection, survival, and predator–prey dynamics. Few studies have explored effects of local and adjacent forest‐stand structure and harvest‐induced edges on nest predation risk. Therefore, during summer 2014, we conducted artificial nest experiments within an intensively managed loblolly pine (Pinus taeda) landscape in Mississippi, USA. We used survival models to quantify effects of forest stand structure and proximity to harvest‐induced edges on apparent predation risk (APR). We conducted vegetation surveys and placed artificial nests (n = 146) at systematic distances from edges between 4 different pine stand types (Class 1: newly established stands; Class 2: 3–5 yr old; Class 3: 5–10 yr old; and Class 4: &gt;10 yr old and postthinned). We sampled 4 stand pairs, each consisting of a Class 1 stand adjacent to a stand type of Class 1 (n = 4), 2 (n = 3), 3 (n = 4), or 4 (n = 4), and developed 15 a priori models relating APR to edge and vegetation characteristics. Apparent predation risk tended to be low and negatively related to edge where adjacent stands featured high proportion of shrub cover and vegetation density. We did not find strong evidence to support increased risk of nest predation near edges. These results were consistent with findings from studies in similar landscape contexts and suggest edges in forest‐dominated landscapes do not increase relative risk of nest predation. Rather, we found that APR was lowest in stands featuring dense shrub and vegetation cover that developed following clearcut harvest. Results of our study highlight some implications of forest harvest on reproductive success of birds, particularly those using early successional vegetation. © 2018 The Wildlife Society.

Small between-year variations in nest predation rates are not related with between-year differences in predator identity

ABSTRACTNest predation is one of the most important causes of nest failure in breeding birds and can vary extensively between sites and years. Different mechanisms governing predation rates may dominate in different years and this annual variation should therefore be evaluated directly. Here we document year-to-year variation in nest predation rates in two ecosystems (forest and salt meadows) within the mid-boreal forest zone to evaluate whether annual variation in nest predation rates are linked with annual variation in predator identity or the ratio between predator types. Year-to-year variation in predation rates was low in all experiments (non-significant differences in experiments 1 and 2), with a significant decrease only from 2005 (0.90%) to 2008 (0.70%), 2009 (0.65%) and 2010 (0.72%) in experiment 3. In addition, random intercept estimates indicated that two sites from experiment 1 showed higher predation rates in year 2 than in year 1. None of these differences were related with differences in apparent predator community structure or predator identity. This suggests that low between-year variation in nest predation rates may be common in areas where the predator communities are stable, and the existing variation cannot be explained by variation in predator identity alone.

Competing for seed dispersal: evidence for the role of avian seed hoarders in mediating apparent predation among oaks

Summary In communities of large‐seeded tree species, generalist seed hoarders often link the temporally variable dynamics of various species in ways that can result in indirect ecological interactions. A special case of such interactions is ‘apparent predation’ – when variation in seed production of one tree species changes the outcome of the interaction between seed hoarders and another tree species from seed dispersal mutualism to predation. We investigated how two species of avian hoarders responded to differences in acorn availability among individual valley oaks (Quercus lobata) and across a landscape dominated by blue oaks (Q. douglasii) to determine whether seed dispersal and predation dynamics result in apparent predation between these oak species. California scrub‐jays (Aphelocoma californica), high‐quality seed dispersers with large spatial scales of resource perception, showed strong numerical and functional responses to individually large Q. lobata acorn crops when landscape‐level acorn crops were low, but the numerical response was not observed when Q. douglasii produced a good acorn crop the subsequent year. In contrast, acorn woodpeckers (Melanerpes formicivorus), which are significant acorn predators, exhibited a consistent functional response to individual Q. lobata acorn crops independent of landscape‐wide availability. Consequently, Q. lobata experienced increased predation and a near absence of high‐quality seed dispersal when Q. douglasii acorns were abundant. Our results suggest that apparent predation among oak species can arise from contrasting responses of generalist seed predators and dispersers to acorn availability on different spatial scales. Thus, the spatial scale of resource perception, which can differ greatly among generalist seed hoarders, may provide a proximate mechanism underlying indirect, temporally variable ecological affects such as apparent predation among sympatric species of large‐seeded trees. A lay summary is available for this article.

Detrivory, competition, and apparent predation by Culiseta longiareolata in a temporary pool ecosystem

Larvae of the mosquito Culiseta longiareolata Macquart have been suggested as important species in desert and Mediterranean temporary pond ecosystems through their strong competitive abilities and as intra-guild predators. We examined their potential predatory effect on larvae of the abundant saltmarsh mosquito Ochlerotatus caspius. We did not find evidence for predatory effects of C. longiareolata on O. caspius larvae. We suggest that, at least in our system, C. longiareolata is an apparent predator. Namely, it does not actively prey on mobile victims, but rather feeds on the carcasses of its fallen competitors additional to its generally immobile food. Hence, we do not expect the occurrence of anti-predator behaviors in response to C. longiareolata presence, including larval development characteristics and oviposition habitat selection.

Wanted dead or alive: Scavenging versus predation by three insect predators

Many generalist insect predators engage in facultative scavenging. If an apparent predator frequently consumes dead prey instead of live prey then the biological control services provided by that predator may be overestimated. The use of unique protein markers on live and dead prey of the same species followed by gut content analysis of the predators is an effective method to distinguish between scavenging and predation events. The frequency of predation and scavenging on third instar Lygus hesperus (Hemiptera: Miridae) prey by Collops vittatus (Coleoptera: Melyridae), Hippodamia convergens (Coleoptera: Coccinellidae) and Chrysoperla carnea (Neuroptera: Chrysopidae) was measured using rabbit IgG and chicken IgG markers. Predators and rabbit IgG-marked dead (cadaver) and chicken IgG-marked live L. hesperus were placed on or adjacent to cotton plants enclosed in small cages for 6h. The plants were then searched for all predators and uneaten prey and examined for the presence of the two proteins by IgG-specific enzyme linked immunosorbent assays (ELISA). The gut analyses revealed that scavenging was more prevalent than predation and that all three predators were facultative scavengers. In addition, direct visual observations of the predators in the cages and the number of C. carnea that went missing during the study suggested that C. vittatus and/or H. convergens were engaging in intraguild predation on C. carnea. When combined with a standard caging procedure the immunomarking procedure used here proved useful for distinguishing scavenging from predation events, which is not possible when using conventional prey-specific ELISA and PCR assays.

Mast species composition alters seed fate in North American rodent-dispersed hardwoods.

Interactions between plants and scatter-hoarding animals may shift from mutualism to predation as a function of the resources available to those animals. Because seed species differ in their nutrient content and defenses to predation, resource selection and cache management by scatter-hoarders, and thus seed fate, may also depend on the relative availability of different seed types. We tracked the fates of tagged Castanea dentata, Quercus alba, and Q. rubra seeds presented to rodents in pairwise combinations and found that C. dentata, which has moderate dormancy prior to germination, survived better in the presence of Q. alba (no dormancy) than with Q. rubra (longer dormancy). Decisions made by scatter-hoarders in response to the composition of available seed resources can alter the relationship between masting and seed dispersal effectiveness in individual tree species and may have influenced the evolution of asynchrony among species-specific masting patterns in temperate forests. In theory, preferential allocation of certain seed species to storage or consumption could also result in indirect apparent predation by one seed species on another.

Safety from predators or competitors? Interference competition leads to apparent predation risk

Prey often react to predation risk by foraging preferentially in the safety of cover rather than in more risky open patches. Yet this pattern of patch use also can be caused by dominant interspecific competitors. We develop a simple theory of this form of apparent predation risk that describes the patch use of an optimal forager confronted with dominant individuals. The theory predicts that subordinate animals should increase their use of safe foraging patches as the density of nearby dominants increases. We tested the theory with meadow voles (Microtus pennsylvanicus) and southern red-backed voles (Myodes gapperi). We used dyadic encounters to confirm that meadow voles are dominant over red-backed voles. We then evaluated their respective foraging patterns in pairs of covered and open patches in 4 adjacent subgrids in an old-field enclosure. Subordinate redbacked voles foraged indifferently between covered and open patches when few meadow voles were present. Red-backed voles increased their use of both patches as the number of nearby meadow voles increased. Givingup densities were lowest, and harvesting efficiency highest, in covered patches when the number of nearby meadow voles was high. These results document competition between the 2 species and suggest that vigilance toward dominant meadow voles magnifies the risk experienced by red-backed voles in open patches. Investigators assessing foraging behavior between ‘‘safe’’ and ‘‘risky’’ patches might misinterpret the competitive effect as predation risk unless they 1st account for competition among foraging individuals.

Rabbits protecting birds: Hypopredation and limitations of hyperpredation

Biological invasions often damage island ecosystems. One such damaging consequence of biological invasions is hyperpredation. Hyperpredation is the increase in predation pressure from a generalist predator following the introduction of an alternative prey, typically a consequence of apparent competition between the two prey. Models for this have been devised that demonstrate this effect. However, hyperpredation may not always occur or may not always occur at the same strength. Here, we investigate how different mechanisms affect the magnitude of hyperpredation: (i) saturation of the predator's functional response, (ii) predator interference and (iii) non-predatory competition among predators. We find that all three mechanisms generally reduce hyperpredation. Predator saturation can actually overturn hyperpredation into hypopredation, an increase in native prey, as a result of apparent predation between the two prey. This occurs when the alternative prey is ‘poisoned prey’, i.e. prey that have a handling time cost greater than the nutritional benefit for the predator. Consuming ‘poisoned prey’ can result in an increase or decrease in predator density. Conversely, we also identify scenarios in which interference and competition may increase hyperpredation. Based on these insights, we conclude that the invasion of established ecosystems by non-native prey can lead to more diverse consequences than previously thought. Potential control measures should take these effects into account.

Predators, facilitators, or both? Re-evaluating an apparent predator–prey relationship

Predators and prey are occasionally observed to comingle in close proximity on coral reefs. Both lethal and non-lethal (i.e. behavioral) effects of predators on prey are well documented. However, observations of apparent predator-prey interactions between the piscivorous twinspot snapper Lutjanus bohar and the herbivorous surgeonfish Acanthurus triostegus suggest that the nature of their association may be context-dependent. The context-dependent nature of some species interactions is well-known, and in some cases a single species has been shown to act as both preda- tor and facilitator to its prey. We present incidental in situ observations suggesting that, in the context of voraciously grazing schools of A. triostegus, this species pair may also engage in a facultative mutualistic relationship. Specifically, we propose that within this context, both species may indirectly derive a benefit through changes in the behavior and/or density of territorial damselfishes driven by both L. bohar and A. triostegus. We provide prescriptions for rigorously testing this hypothesis and suggest that re-evaluation of this, and possibly other, ostensibly exclusive predator-prey pairs in marine systems may reveal unexpected relationships. Given the relative lack of examples of such interactions involving the same predator acting as both facilitator and predator from marine versus terrestrial systems, coupled with this preliminary evidence, we propose that this topic is ripe for exploration.

Comparative Die-off ofEscherichia coli0157:H7 and Fecal Indicator Bacteria in Pond Water

In situ and in vitro experiments were performed to assess the effects of solar radiation and predation by indigenous microflora on the relative die-off rates of a toxigenic strain of Escherichia coli O157:H7, commensal E. coli, and fecal enterococci in surface waters from ponds in agricultural watersheds. The objective of these experiments was to discern a mechanism of persistence of E. coli O157:H7 in surface waters compared to fecal indicator bacteria. Results of these experiments indicated that E. coli and fecal enterococci were affected by both insolation and apparent predation; whereas E. coli O157:H7 appeared to be resistant to both of these environmental stressors. The number of days to reach 99% die-off (T(99)-values) for E. coli O157:H7 was significantly greater than that for the indicator bacteria. The capacity to prolong die-off may be connected to the apparent persistence of E. coli O157:H7 in surface waters.

Pronghorn (Antilocapra americana) Locked in Fight Becomes Prey of Coyotes (Canis latrans)

We report apparent predation by coyotes (Canis latrans) on one of two male pronghorns (Antilocapra americana) that were locked together. When the locked pronghorns first were spotted at 2030 h, both were alive, one standing and the other on the ground wounded by a horn of his opponent. At ca. 0230 h, four coyotes were seen within 150 m of the pronghorns. At 0630 h, the wounded pronghorn had been partially eaten, presumably by the coyotes, and the other pronghorn freed himself from the carcass and walked away.

Wolf (&lt;i&gt;Canis lupus&lt;/i&gt;) Predation of a Polar Bear (&lt;i&gt;Ursus maritimus&lt;/i&gt;) Cub on the Sea Ice off Northwestern Banks Island, Northwest Territories, Canada

We describe the apparent predation of a polar bear (Ursus maritimus) cub by wolves (Canis lupus) on the sea ice just off the northwest coast of Banks Island, Northwest Territories, Canada. On 20 April 2004, while following the tracks of a female bear and two cubs-of-the-year in the snow during a helicopter survey, we noted that the bear tracks had been joined by several sets of wolf tracks. After following both sets of tracks for about 1 km, we observed a disturbed area in the snow with numerous overlying tracks. Upon landing and searching the site, we found the remains of a polar bear cub that the wolves had successfully separated from its mother and killed. This is only the second documented observation ever made of a polar bear killed by wolves.