Leaving food in your garden for wild animals might seem like kindness, but it actually forces them into competition for resources and causes conflict with humans, scientists have warned.
US academics studied carnivores including foxes and martens in seven areas of the Great Lakes region, in the northeastern US.
In some cases the animals drew more than 50 per cent of their diet from human sources.
The findings suggest that the British habit of leaving food out for animals like foxes could be having unintended consequences.
The study, published in the journal Proceedings of the National Academy of Sciences, found a consistently high level of human food was being eaten by carnivores across all areas where humans were prevalent.
Lead author Dr Phil Manlick, of the University of Wisconsin–Madison, said the pattern is leading to a greater number of encounters between humans and animals, which has negative consequences such as harm caused to pets and diseases spread between domestic and wild animals.
In the US bears, wolves and coyotes have increasingly been spotted in towns and cities, drawn by poorly-secured bins and food waste.
But he said the findings were relevant to areas around the world, where increasing urbanisation and the growth of suburbia has led to more and more encounters with animals once confined to wild environments.
In the UK city-dwellers have reported encounters with urban foxes, which can, albeit very rarely, present a danger to young children.
“I don’t think these results necessarily imply that there may be direct conflict, attacks on people, I really don’t think that’s true at all. But I do think that humans and carnivores are going to increasingly come in contact with each other and we need to adapt to that,” said Dr Manlick.
The researchers gathered bone and fur samples from animals living in different areas and used chemical analysis to glean details of their diet.
Animals which had evolved to coexist by having different preying habits were now in competition for the same food, the study found.
The findings also suggested that smaller or less common predators could suffer by coming into conflict with larger, more dominant species.
He added: “Carnivores are eating new foods and it’s leading to significant amounts of dietary overlap.
“We know from systems in North America, Asia, Africa or elsewhere, that when carnivores overlap in their diets, it leads to conflict between each other.
“They have adapted over millennia the teeth and claws and they will readily use those against each other, if it comes down to it.”
It could also have unknown impacts on the food chain, as predators shift their diets away from their usual fare of smaller rodents.
Dr Manlick added that living on human food could either mean predator populations go up, putting more pressure on the animals they typically eat, or it could mean the relationship between predator and prey collapses entirely.
“Are we going to get hyper predation, a really strong predator effect? Or are they basically going to become predators without teeth, per se, without having any real impact on the ecosystem? I just don’t think we know that right now.”