Anthropogenic Food Research Articles

Eating in the city: Experimental effect of anthropogenic food resources on the body condition, nutritional status, and oxidative stress of an urban bioindicator passerine.

Urban areas provide a constant and predictable supply of anthropogenic processed food. The House Sparrow (Passer domesticus Linnaeus, 1758), a declining urban bioindicator species, has recently been reported to have a high level of oxidative stress, with urban diet or pollutants proposed as the potential cause. In this study, we aimed to experimentally determine the effects of two urban trophic resource types (bar snack food leftovers and pet food) on sparrows' physical condition, plasma biochemical nutritional parameters, and blood oxidative status in captivity. To exclude the potential previous effect of urban pollutants, 75 House Sparrows were captured from a rural area in SE Spain and kept in outdoor aviaries. Individuals were exposed to one of three diet treatments: control diet (fruit, vegetables, poultry grain mixture), bar snack diet (ultra-processed snacks), or cat food diet (dry pellets) for 20 days. Blood samples were collected before and after diet treatments to analyze the relative change rates of 12 variables, including physical condition, nutritional status, and oxidant-antioxidant status. A principal component analysis was run to identify gradients of variables covariation, and Generalized Linear Mixed Models were used to determine the effect of diets on each selected PC and on raw variables. The bar snack diet led to signs of anemia and malnutrition, and females tended to lose body condition. The cat food diet increased oxidative stress indicators and protein catabolism. Unbalanced urban diets can affect the body condition and nutritional physiology of House Sparrows and may also induce oxidative stress despite the absence of environmental pollution.

A multidimensional framework to quantify the effects of urbanization on avian breeding fitness

AbstractUrbanization has dramatically altered Earth's landscapes and changed a multitude of environmental factors. This has resulted in intense land‐use change, and adverse consequences such as the urban heat island effect (UHI), noise pollution, and artificial light at night (ALAN). However, there is a lack of research on the combined effects of these environmental factors on life‐history traits and fitness, and on how these interactions shape food resources and drive patterns of species persistence. Here, we systematically reviewed the literature and created a comprehensive framework of the mechanistic pathways by which urbanization affects fitness and thus favors certain species. We found that urbanization‐induced changes in urban vegetation, habitat quality, spring temperature, resource availability, acoustic environment, nighttime light, and species behaviors (e.g., laying, foraging, and communicating) influence breeding choices, optimal time windows that reduce phenological mismatch, and breeding success. Insectivorous and omnivorous species that are especially sensitive to temperature often experience advanced laying behaviors and smaller clutch sizes in urban areas. By contrast, some granivorous and omnivorous species experience little difference in clutch size and number of fledglings because urban areas make it easier to access anthropogenic food resources and to avoid predation. Furthermore, the interactive effect of land‐use change and UHI on species could be synergistic in locations where habitat loss and fragmentation are greatest and when extreme‐hot weather events take place in urban areas. However, in some instances, UHI may mitigate the impact of land‐use changes at local scales and provide suitable breeding conditions by shifting the environment to be more favorable for species' thermal limits and by extending the time window in which food resources are available in urban areas. As a result, we determined five broad directions for further research to highlight that urbanization provides a great opportunity to study environmental filtering processes and population dynamics.

Scavengers use natural and anthropogenic resources connecting protected areas with surrounding lands

Anthropogenic food subsidies can alter ecosystem processes, such as competition, predation, or nutrient transfer, and may strongly affect protected areas. Increasing recreation and ecotourism often create food subsidies, especially in the surrounding lands through fast-growing gateway communities. How the effects of these subsidies extend into protected areas when animals move across boundaries remains largely unexplored. We addressed this question by studying the movement and foraging of common ravens (Corvus corax), opportunistic scavengers that are well known to feed on predator kills and on anthropogenic food subsidies. We analyzed spatiotemporal data from 57 global positioning system (GPS)-tagged ravens, trapped within or close to Yellowstone National Park, to study their seasonal use of natural and anthropogenic food sources. Although Yellowstone National Park contains a full suite of native predators and ravens can be observed at virtually every kill site, we show that anthropogenic subsidies were utilized to a much greater extent than other natural resources, especially during winter. Important subsidies included gut piles of harvested game animals left by hunters, fat present on wastewater settling ponds, roadkill, and waste from agricultural and urban activities. These subsidies were distributed over vast areas beyond Yellowstone National Park. During fall/winter, ravens traveled longer distances (21.9 vs. 13 km) and spent more time outside Yellowstone National Park (73% of GPS points outside), mostly feeding on anthropogenic subsidies, than in spring/summer (42% of GPS points outside). This difference between seasons was more pronounced for individuals holding territories within the protected area than for those without territories. The large area over which ravens used anthropogenic food subsidies (within more than 100 km of Yellowstone National Park) affects the park’s raven population and the scavenging services they provide. We suggest that the scale of resource use must be considered by managers seeking to control expanding raven populations elsewhere.

Behavior‐specific habitat selection by raccoons in the Prairie Pothole Region of Manitoba

AbstractPatterns of resource selection depend upon an animal's behavioral state. Because management strategies are often crafted from an understanding of animal space use, incorporating behavior explicitly into analyses of resource selection has the potential to improve outcomes. In the Prairie Pothole Region of Manitoba, Canada, raccoons (Procyon lotor) are a nest predator of waterfowl, but it is unclear how raccoons use this landscape during the waterfowl nesting season. Our objective was to use high‐resolution global positioning system (GPS) telemetry to differentiate among behaviors by raccoons and evaluate behavior‐specific habitat selection during the waterfowl nesting season. We collected approximately 32,000 locations from 33 animals during the 2018, 2019, and 2021 nesting seasons, amounting to 632 animal‐night's worth of movement data. We used hidden Markov models (HMM) to fit 4‐state models to the movement trajectories, classified observations into discrete behaviors, and fit behavior‐specific random forest resource selection models to evaluate the relative importance of habitat features on selection. Proximity to a wetland was the most important variable contributing to selection for the resting, foraging, and slow travel states. Probability of use was as high as 95% within or immediately adjacent to a wetland for animals engaged in those behaviors, and our best HMM predicted increasing probability of switching from resting or foraging to directed travel with increasing distance from a wetland edge. Human‐use sites were also important to foraging animals, suggesting raccoons subsidize their diet with anthropogenic food resources during spring and summer. These results illuminate the complexity of habitat selection by a waterfowl predator in this patchy landscape, allowing managers to develop effective conservation strategies (e.g., wetland prioritization and conservation, elimination of anthropogenic subsidies) where raccoons are having a disproportionate effect during the waterfowl nesting season.

Anthropogenic Neighborhood Impact on Bacterial and Fungal Communities in Polar Bear Feces.

Climate changes cause a dramatical increase in the ice-free season in the Arctic, forcing polar bears ashore, closer to human settlements associated with new and non-natural food objects. Such a diet may crucially transform the intestinal microbiome and metabolism of polar bears. The aim of this study was to characterize changes in the gut bacterial and fungal communities resulting from the transition to anthropogenic food objects by the means of 16S and ITS metabarcoding. Thus, rectal samples from 16 wild polar bears from the Kara-Barents subpopulation were studied. Human waste consuming resulted in a significant increase in the relative abundance of fermentative bacteria (Lactobacillaceae, Leuconostocaceae, and Streptococcaceae) and a decrease in proteolytic Enterobacteriaceae. However, the alpha-diversity parameters remained similar. Also, for the first time, the composition of the fungal community of the polar bear intestine was determined. Diet change is associated with the displacement of eurybiontic fungi (Thelebolus, Dipodascus, Candida (sake), and Geotrichum) by opportunistic Candida (tropicalis), Kazachstania, and Trichosporon. Feeding on human waste does not cause any signs of dysbiosis and probably leads to adaptive changes in the bacterial microbiome. However, the emergence of fungal facultative pathogens increases the risk of infections.

An ethogram identifies behavioural markers of attention to humans in European herring gulls (Larus argentatus).

Herring gulls (Larus argentatus) are one of few species thriving in anthropogenic landscapes. Their history of urbanisation and familiarity with people makes them a good target for studies of human-wildlife interactions. Previous research highlights a connection between food-stealing behaviour, success in anthropogenic areas, and increased attention towards humans, raising questions about the exact extent of a gull's knowledge of human food cues. To explore these, behavioural responses to human cues in a food-related context were investigated and presented in a systematic ethogram, which identified three distinct markers of attention. Head turns, approaches, and angular body position all differed significantly between control and food conditions, showing that attention towards humans in a food-related context was upregulated and reflected in behaviour. In food condition trials, head turns occurred more often and gulls faced more towards the experimenter with occasional approaches that were never seen in control conditions. Acoustic and behavioural human food-like cues alone seemed insufficient to elicit these responses, indicating that gulls specifically paid attention to the details of human behaviour or had specific knowledge of anthropogenic food items. These results show situation-dependent attentional modulation in gulls and provide a description of attentive behaviours that can be used in further study.

Drastic reduction of the population distribution of White Storks predicted in absence of landfills

AbstractOrganic waste production has greatly increased following human sprawl and led to the development of landfills in recent decades. This abundant and reliable anthropogenic food source has favored several species, some of which consequently became overabundant. Landfills present hazards to wildlife, which may suffocate on plastic materials, tangle on cords, and get exposed to pollutants and pathogens. In response to environmental and public health concerns over the maintenance of landfills, the European Commission proposed to close the landfills. Our objective was to determine the impact of Landfill European Directive on the White Stork (Ciconia ciconia) whose population recovery and growth was linked to landfill exploitation. We implemented species distribution models to project future distribution in the absence of landfills in the Community of Madrid (Spain). Habitat suitability was estimated based on nest occurrence and we included data from land cover types, human population density, and two different climate change scenarios (i.e. emissions in low and high shared socioeconomic pathways). Given that protection measures, particularly implemented in protected areas, were associated with population recovery, we also evaluated the overlapping degree between protected areas and projected distribution. Our models predicted a sharp decline in breeding population distribution with landfill closure, reaching values similar to the 1984 breeding census when the species was categorized as threatened. Our results also suggest a decrease in maximum habitat suitability. Climate change also contributed to a reduction in breeding population distribution given model predictions for the extreme emission pathway (ssp5). Measures such as gradual change in landfill management, continuous monitoring of breeding populations, and evaluation of the White Stork use of natural feeding areas before and after landfill closure, should be considered.

Using behavioral studies to adapt management decisions and reduce negative interactions between humans and baboons in Cape Town, South Africa

AbstractUnderstanding the behavioral ecology of wildlife that experiences negative interactions with humans and the outcome of any wildlife management intervention is essential. In the Cape Peninsula, South Africa, chacma baboons (Papio ursinus) search for anthropogenic food sources in both urban and agricultural areas. In response, the city of Cape Town and private farmers employ “rangers” to keep baboons within the Table Mountain National Park. In this study, we investigated the success of rangers' intervention in keeping baboons in their natural habitat. Based on our findings in year one, we recommended adjustments to the rangers' management strategy in year two. We recommended improved consensus of actions toward baboons (that is, when/where to herd them), and the construction of a baboon‐proof fence around one of the farms that provided a corridor to urban areas. During the 2 months following recommendations, these interventions combined resulted in a significant reduction in the time baboons spent in both urban and agricultural land. Our case study illustrates the importance of integrating research findings into ongoing management actions to improve both human livelihoods and baboon conservation through an adaptive management framework. We expect similar approaches to be beneficial in a wide range of species and contexts.

Evaluating the dependence of opportunistic Yellow‐legged Gulls (Larus michahellis) on marine habitat and fishing discards

Several bird species benefit from anthropogenic food subsidies, such as landfills and fishing discards, that are being reduced owing to introduced legislation. For instance, since 2019, Europe has passed legislation to reduce dramatically the amount of fisheries discards through the Landing Obligation (LO), which states that all fish species under Total Allowable Catch (TAC) should not be discarded at sea. This European discard ban is expected to impact some gulls, as several gull populations have been observed to be heavily reliant on this resource. In this work, GPS tracking data from adult Yellow‐legged Gulls Larus michahellis and Vessel Monitoring System (VMS) data (i.e. detailed data of the spatial distribution of fishing vessels) are used to determine the utilization of the marine habitat and the level of interaction of gulls with fishing activity offshore and discards in the south‐eastern part of the Bay of Biscay. We found that these gulls had a low use of the marine habitat (ca. 15%) compared with terrestrial habitats, in contrast to the ca. 40% of the diet of this population which comprises marine prey. Furthermore, we detected that most of the gull tracking positions at sea did not interact with the fishing vessels (an overlap of 21.5% between gulls and VMS data). Conversely, other gull populations of the Iberian Peninsula were found to depend much more strongly on fishing activity. Therefore, the Yellow‐legged Gull population of the SE Bay of Biscay did not obtain most of its fish prey from interactions with offshore fishing activity but most possibly by taking fish remains in harbours and by feeding themselves. Consequently, we expect a minimal effect of the European policies oriented to ban fishing discards offshore on this population, which would be more affected by policies directed towards the reduction of food availability in landfills or fish landing management in harbours.

Inter-species stimulus enhancement: herring gulls (Larus argentatus) mimic human food choice during foraging.

Herring gulls (Larus argentatus) are one of few species that thrive in anthropogenic landscapes, and their familiarity with people makes them an excellent target for studies of inter-species social cognition. Urban gulls pay attention to human behaviour in food-related contexts and, thus, we set out to investigate whether such cues can influence a gull's attention to and choice of potential food items in their environment. Herring gulls were given free choice of two differently coloured anthropogenic food items in the presence of a demonstrator, who was either sitting still or eating food from an item that matched one of the presented ones. We found that a demonstrator eating significantly increased the likelihood of a gull pecking one of the presented items. Furthermore, 95% of pecks were directed toward the presented food item that colour-matched the demonstrator's food item. The results showed gulls were able to use human cues for stimulus enhancement and foraging decisions. Given the relatively recent history of urbanization in herring gulls, this cross-species social information transfer could be a by-product of the cognitive flexibility inherent in kleptoparasitic species.

The paleo-synanthropic niche: a first attempt to define animal’s adaptation to a human-made micro-environment in the Late Pleistocene

Synanthropic behavior, i.e., the behavior of wild animals that benefit from a shared ecology with humans, has existed long before the sedentarization of Homo sapiens during the Neolithic, around 10,000 years ago. This study describes and discusses the concept of an older animal-human relationship: paleo-synanthropic behavior and the associated paleo-synanthropic niche. Key features of this new niche are anthropogenic food waste from mobile hunter-gatherers as a stable food base for small opportunistic scavengers and a human-near environment safe from large predators. By linking the niche to human behavior rather than to a specific location or structure, this niche was accessible for a long time, even in the Late Pleistocene. Like modern synanthropic animals, members of the paleo-synanthropic niche experienced an increase in population density and a decrease in home range. This, in turn, made it easier for humans to capture these animals and use them as resources for meat, fur, or feathers, as seen in the zooarchaeological record of many European Late Pleistocene sites. As a disadvantage, diseases such as zoonoses may have spread more easily.

Resource predictability modulates spatial-use networks in an endangered scavenger species

BackgroundChanges in human-induced resource availability can alter the behaviour of free-living species and affect their foraging strategies. The future European Landfill Waste Directive and Circular Economy Action Plan will reduce the number of predictable anthropogenic food subsidies (PAFS), above all, by closing landfills to preclude negative effects on human health. Obligate avian scavengers, the most threatened group of birds worldwide, are the most likely group of species that will be forced to change their behaviour and use of space in response to landfill site closures. Here, we examine the possible consequences of these management decisions on the foraging patterns of Egyptian vultures (Neophron percnopterus) in an expanding population in the Iberian Peninsula.MethodsWe tracked 16 individuals in 2018–2021, including breeders and non-breeders, and, using a combination of spatial-use and spatial-network modelling, assessed landscape connectivity between key resources based on movement patterns. We then carried out simulations of future scenarios based on the loss of PAFS to predict likely changes in the movement patterns of both non-breeders and breeders.ResultsOur results show that foraging strategies in non-breeders and breeders differ significantly: non-breeders performed more dispersal movements than breeding birds across a spatial-use network. Non-breeding and breeding networks were found to be vulnerable to the removal of central foraging areas containing landfill sites, a highly predictable resource, while perturbation analysis showed dissimilar foraging responses to the gradual reduction of other predictable resources. Under a context of the non-availability of landfills for breeders and non-breeders, vultures will increase their use of extensive livestock as a trophic resource.ConclusionsFuture environmental policies should thus extend the areas used by scavengers in which livestock carcasses are allowed to remain in the wild, a strategy that will also mitigate the lack of food caused by any reduction in available waste if landfills close. In general, our results emphasize the capabilities of a spatial network approaches to address questions on movement ecology. They can be used to infer the behavioural response of animal species and, also demonstrate the importance of applying such approaches to endangered species conservation within a context of changing humanized scenarios.

New mesocarnivore at the doorstep of Central Europe: historic development of golden jackal (Canis aureus) population in Slovenia

Golden jackal (Canis aureus) has dramatically increased its distribution and abundance in Europe. Expansion is now reaching parts of Central, Northern, and Western Europe, where jackal occurrences are mainly limited to vagrants or single territorial groups. Currently, it is hard to predict future development of jackal populations in these regions, as it remains unclear whether environmental conditions here could enable population growth similar to the jackal core areas in the South-eastern Europe. We used a combination of a literature review, opportunistically collected data and systematic acoustic surveys to study historic development of golden jackal population in Slovenia, a Central European country that jackals started colonizing 70 years ago and which could serve as a model for other countries at the expansion frontier due to its resemblance in environmental conditions. After the initial expansion waves reached Slovenia in the 1950s and 1980s, jackal presence became more permanent since 2000s. This is also the period when first territorial groups and reproductions were confirmed, but it was not until the following decade for the number of records to start exhibiting an exponential growth. By 2016–2017, the minimum densities in lowlands reached 0.06–0.29 jackal territorial groups/10 km2, which is still lower compared to the core areas in the Balkans and the Pannonian Basin. This study demonstrates that jackals can successfully colonize and spread across a forested Central-European country with lower availability of anthropogenic food resources, although in such conditions, it can take several decades of sporadic existence before population progresses into exponential growth similar to jackal populations in the European core areas.

Proximity to anthropogenic food sources determine roosting and nesting prevalence of feral pigeons (Columba livia) in a tropical city

AbstractThe feral pigeon (Columba livia) is a globally commensal bird that can cause dis‐amenities such as soiling and is a potential vector of various diseases. Aside to limiting food as a management strategy, reducing the availability of roosting and nesting sites can help regulate feral pigeon populations. Despite their prevalence, current knowledge of their roosting and nesting preferences is lacking.Feral pigeons commonly use railway viaduct expansion gaps in Singapore for roosting and nesting. These gaps provided an ideal experimental platform to examine feral pigeon roost and nest site selection while controlling for differing cavity sizes which can significantly affect their reproductive success and site selection decisions. We also conducted an in‐situ experiment to test the efficacy of nest removal as a management option.Our nationwide surveys of 80.3 km of railway viaducts and 6048 gaps revealed that feral pigeon day roosting and nesting preferences are influenced by structural height and more importantly, their proximity to human food sources. There was a significantly higher probability of feral pigeon roosting in a gap if it had more pigeon feeding incidences in its vicinity and was higher. The probability of feral pigeon nesting in gap was higher if it was closer to a railway station, lower and further from water bodies.In our field experiment, we did not find any significant differences in the proportions of the abundances of feral pigeon to other urban commensal bird species at the gaps before and after nests were removed.Overall, our results suggest that a concerted effort to reduce anthropogenic food availability to feral pigeons is central in limiting their reproductive success and controlling their population.

Changes in the feeding ecology of an opportunistic predator inhabiting urban environments in response to COVID-19 lockdown.

Urban-dwelling species present feeding and behavioural innovation that enable them to adjust to anthropogenic food subsidies available in cities. In 2020, the SARS-CoV-2 virus outbreak resulted in unprecedented reduction in the human activity worldwide associated with the human lockdown. This situation opened an excellent opportunity to investigate the capability of urban wildlife to cope with this anthropopause event. Here, we investigated the effects of the COVID-19 lockdown on the feeding strategies of the urban yellow-legged gull (Larus michahellis) population inhabiting the highly dense city of Barcelona (NE Spain). We compared the diet of chicks (through stomach content and stable isotope analyses) sampled randomly around the city of Barcelona before (2018 and 2019), during (2020) and after (2021) the COVID-19 lockdown. The results revealed that the anthropopause associated with the lockdown had an effect on the diet of this urban-dwelling predator. The diversity of prey consumed during the lockdown was lower, and consumption of urban birds (pigeons and parakeets) and marine prey (fishery discards and natural prey) decreased during the year of lockdown. Although it was not analysed, these diet changes probably were associated with variations in the availability of these resources due to the decrease in human activity during the lockdown. These results demonstrate the trophic flexibility of urban-dwelling species to cope with the changes in the availability of human-related anthropogenic resources in urban marine ecosystems.

Dietary preference of striped hyena in the anthropogenic landscape of Rajasthan, India

Understanding the dietary patterns of large carnivores is a key feature of their niche and addresses their ecological role in ecosystems. The striped hyena (Hyaena hyaena) is a large carnivore distributed in many arid and semi-arid regions of the world and its diet is largely understudied in its range. We studied the dietary patterns of striped hyenas in the anthropogenic landscape, located in the semi-arid region of Rajasthan, India. We collected and analyzed a total number of 127 scat samples from November 2019 to February 2022. The relative biomass and frequency of occurrence of the large-sized prey species (>30 kg) were higher in the striped hyena's diet. However, the species requires a wide range of smaller prey to enrich its diet and a total of twenty-one prey species have been recorded in the hyena diet. The diet diversity of the striped hyena computed by the Shannon-Weiner Index (H) was 3.28. The proportion of prey in the scats indicated that very large to large and medium-sized prey accounted for 95.7% of total dietary biomass and was mostly preferred by striped hyenas, which was probably consumed through scavenging. Livestock (cows, buffaloes, sheep, camels, and dogs) accounted for 56.54% of total dietary biomass. The higher amount of presence of livestock mammals in the scats suggests that striped hyenas may frequently visit human settlement areas, which could be influenced by high carcass availability. The presence of small prey such as mongoose, hares, foxes, and rats indicate that the striped hyenas might partially hunt the smaller animals or opportunistic feed. This study added to our understanding of the striped hyena's feeding ecology in areas where anthropogenic food is quite abundant compared to wild prey. Hence hyenas benefit from anthropogenic food scavenging, whereas humans benefit from the non-lethal nature of hyenas and waste removal.

The use of cellular telecommunication towers as nesting sites by pied crows (Corvus albus) in an urban mosaic landscape

Corvids are known for their urban exploitation, often using artificial infrastructure to roost and nest. In many areas of its distribution range, the pied crow (Corvus albus) is often common in areas of anthropogenic land use, often breeding and foraging near human settlements. In this study, we monitored pied crow use of cellular telecommunication towers as nesting sites in Pietermaritzburg, South Africa, during three breeding seasons. We found that of the 36 towers situated across the urban mosaic landscape, pied crows used 17 (47.2%) as nesting sites while 19 were not used. Many towers were used in subsequent years as nesting sites. Overall, 41 pied crow nests on towers in urban mosaic landscapes were counted by the end of the study. Towers had a mean (± SE) distance of 1595.2 ± 151.0 m between them and were located mainly in the suburbs of Edendale and Northdale. As shown by the hotspot analysis and spatial distribution of used and unused towers, it was unclear why some towers were not being used as nesting sites. We assessed the relationship between pied crow nesting sites and land cover features. We found that tower nesting was best explained by cropland (wi = 0.58), forest (wi = 0.94), grassland (wi = 0.66), schools (wi = 0.56) and relief (wi = 0.56). The continued persistence of pied crows in urban mosaic landscapes with natural and /or managed green spaces, the availability of anthropogenic infrastructure and food in these, and their behavioural plasticity will likely increase their numbers in such landscapes.

An Ongoing Shift in Mammalian Nest Predators of Yellow-billed Loons in Arctic Alaska

The Coastal Plain of northern Alaska is an important nesting area for a variety of avian species, where the productivity of ground-nesting species can be strongly influenced by nest predators. Recently, the density of red foxes (Vulpes vulpes) has increased in many areas of the Arctic, likely because of climate warming as well as the availability of anthropogenic food sources during winter. In areas where they occur sympatrically, red foxes can outcompete and kill the smaller Arctic fox (Vulpes lagopus). There is considerable dietary overlap between the fox species, but if the red fox is a more successful nest predator, this ongoing shift in canid species could have important implications for ground-nesting species like the Yellow-billed Loon (Gavia adamsii). We examined time-lapse photographs from 186 nests of Yellow-billed Loons in northern Alaska during the years 2008 – 15 and 2019 for the presence of foxes and other nest predators and quantified nest predation by species. Although both Arctic and red foxes were photographed near nests, we found that all successful predation of Yellow-billed Loon nests by foxes was attributable to red foxes, which were the second most frequent predator of Yellow-billed Loon nests after Glaucous Gulls (Larus hyperboreus). Arctic foxes photographed at Yellow-billed Loon nests were unsuccessful at displacing incubating loons. Several data sources suggest that the prevalence of red foxes has increased in Arctic Alaska over the last three decades, a change that is likely to have negative impacts on the nesting success of Yellow-billed Loons and possibly other large waterbirds.

The effect of the temperature on local differences in the sex ratio of Mallards Anas platyrhynchos wintering in an urban habitat

In Mallard, as in other ducks of the northern hemisphere, males outnumber females in wintering flocks and the temperature seems to be one of the most important factors shaping the sex ratio at a given site. In this study, we checked the influence of winter harshness on the sex ratio of Mallards overwintering in urban waterbodies with an emphasis on differences at the local scale within a single town. Our study shows that in harsh winter seasons, there was a lower share of males among wintering Mallards. It seems that females, despite their smaller body size and higher specific metabolic rate, found favourable conditions in the urban area during cold weather. Towns are characterized by a milder winter climate than rural areas, moreover birds profit from the supplementary feeding by humans. In severe weather conditions, females remained in urban waterbodies together with their paired mate, whereas unpaired males possibly left the town in search of sites with less competition, as they occupy a lower position in the flock hierarchy than paired individuals. We also found such differences on a local scale, with the proportion of males decreasing with decreasing temperature. Obtained results suggest that the sex- and status-dependent response to even a slight temperature change during the winter period is probably the most important factor shaping the variation in the proportion of male and female Mallards in flocks, at least in areas with a high abundance of anthropogenic food, which is likely to weaken competition between the sexes for resources.

Black Bear Behavior and Movements Are Not Definitive Measures of Anthropogenic Food Use

Increasing human-bear conflicts are a growing concern, and managers often assume bears in developed areas are food-conditioned. We examined the relationship between human-bear conflicts and food conditioning by analyzing isotopic values of hair from black bears (Ursus americanus floridanus) involved in research (n = 34) and conflicts (n = 45). We separated research bears into wild and developed subgroups based on the impervious surface within their home ranges and separated conflict bears based on observations of human food consumption (anthropogenic = observations; management = no observations). We initially assumed wild bears were not food conditioned and anthropogenic bears were. However, using isotopic values, we classified 79% of anthropogenic bears and 8% of wild bears as food conditioned. Next, we assigned these bears to the appropriate food conditioned category and used the categorizations as a training set to classify developed and management bears. We estimated that 53% of management bears and 20% of developed bears were food conditioned. Only 60% of bears captured within or using developed areas showed evidence of food conditioning. We also found that δ13C values were a better predictor of anthropogenic foods in a bear's diet than δ15N values. Our results indicate that bears in developed areas are not necessarily food conditioned and caution against management actions based on limited observations of bear behavior.