The expansion of human settlements has led to a significant overlap between wild animal habitats and areas of human activity. This interface has given rise to synanthropic species, which are types of wildlife that thrive in environments modified by people. One concerning resource these animals exploit is human waste, transforming discarded food and materials into an unnatural, readily available food source. Trash scavenging is a worldwide issue, driven by the volume of waste generated and the opportunistic nature of animals adapting to human expansion. The availability of this anthropogenic food is fundamentally altering the ecology and behavior of numerous species.
Common Scavengers of Urban Areas
Mammalian Scavengers
The raccoon (Procyon lotor) is the most recognized mammalian scavenger in North America, infamous for its dexterity in manipulating garbage can lids. These nocturnal foragers are omnivorous and consistently raid residential bins and dumpsters for food scraps. Bears, including American black bears and Eurasian species, are highly opportunistic feeders that frequent open landfills and poorly secured dumpsters, using strength to break into containers.
Coyotes (Canis latrans) are highly adaptable and thrive in urban areas by utilizing waste as a food subsidy, contributing to their expanding range and population density. In Europe and Asia, the Red Fox is a common urban resident whose diet often includes a substantial proportion of human food waste near dwellings. Opossums are less adept at opening secured containers, but they readily scavenge scraps from trash bags or bins that other animals, like raccoons or skunks, have already overturned.
Avian and Other Scavengers
Avian species are significant consumers of human refuse, often dominating feeding activity at large municipal landfills. Gulls, such as the Yellow-legged Gull, have increased their populations by relying on fishery discards and garbage dumps as a predictable source of sustenance. Crows and ravens are intelligent birds that frequently pick through exposed trash bags and open containers, often transporting food items over distances. These birds, along with rodents like rats and mice, can easily gnaw through soft packaging and trash bags, creating access for larger, less subtle scavengers.
Drivers Behind Waste Consumption
The primary factor attracting wildlife to trash is the high caloric density of discarded human food, offering a substantial energy return for minimal foraging effort. Human food waste is often rich in fats and carbohydrates, providing an easy source of energy that is far more concentrated than most natural forage. This predictability and abundance contrast sharply with the often-sparse and seasonally variable nature of natural food sources, making trash an attractive and reliable alternative.
Habitat encroachment plays a major role, as human development reduces the availability of natural foraging grounds, pushing wildlife closer to human-generated resources. Animals that are naturally omnivorous or opportunistic, like raccoons, are pre-adapted to exploit this new food niche, seeing human habitations as a consistent, year-round buffet. For species that must build up fat reserves before periods of scarcity, such as bears or raccoons preparing for winter, the readily accessible, high-calorie waste is an irresistible draw.
This behavior can become learned, as younger animals observe and mimic successful scavenging techniques from their social group. A reliable source of sustenance allows local populations to increase their carrying capacity, meaning more individuals can survive and reproduce in a smaller area than the natural environment would typically support. The combination of easy energy, habitat loss, and learned behavior creates a powerful incentive for wildlife to become dependent on human waste.
The Health and Behavioral Toll on Wildlife
A diet based on human trash introduces severe health risks to wildlife. Animals frequently ingest non-digestible materials like plastic bags, packaging, and microplastics, which can cause internal blockages, false feelings of fullness, and subsequent starvation. Sharp objects, such as broken glass, metal shards, or tin cans, can lead to severe internal injuries, lacerations, or slow, painful deaths.
Entanglement is a widespread physical danger, as discarded items like rubber bands, tea bag strings, and plastic six-pack rings can constrict limbs, necks, or antlers, leading to injury, infection, or suffocation. While high in calories, a trash-based diet is often nutritionally unbalanced, potentially leading to deficiencies that affect long-term health, reproductive success, and and overall fitness.
The reliance on human waste also causes significant behavioral changes in wildlife populations. Animals become habituated to human presence and lose their natural wariness, which increases the frequency of human-wildlife conflict and can result in retaliatory actions against the animals. Increased population densities around concentrated food sources, such as landfills or urban neighborhoods, facilitate the rapid spread of infectious diseases like rabies and canine distemper among species like raccoons and coyotes. This proximity and interaction at feeding sites also increases the risk of disease transmission between wild animals, domestic animals, and humans.