Photograph by Joel Sartore, Nat Geo Image Collection
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Birdfeeders, while popular among homeowners, can have downsides for wildlife. But are those issues outweighed by their benefits?

Photograph by Joel Sartore, Nat Geo Image Collection

Why you shouldn't feed wild animals (except maybe birds)

Many people draw wildlife into their backyards by putting out birdseed, saltlicks, and other food sources, but experts say doing so can lead to trouble.

Whether it’s a birdfeeder on an apartment terrace or a corn feeder for backyard deer, many people enjoy attracting wildlife with the offer of food.

But experts say doing so can have dangerous consequences for both animals and humans.

Feeding sites bring many different kinds of animals into the same small area, which can turn into a hotbed for disease transmission and parasites, says Jeannine Fleegle, a wildlife biologist for the Pennsylvania State Game Commission.

For instance, scientists suspect a fatal disease affecting deer known as Chronic Wasting Disease is spread by exposure to urine, saliva, and feces—all of which get mixed together when animals congregate at feeders.

“Feed used to attract deer will draw turkeys, squirrels, racoons, opossums, rodents, skunks, and foxes, directly or indirectly,” says Fleegle. “And just as feed sites increase risk of disease exposure and transmission in deer and elk, these sites will do the same for these species.”

Don't Feed the Bears

Canine distemper, parvovirus, leptospirosis, Baylisascaris, and avian pox are all diseases or parasites that can be spread at feeding sites.

“Feeding wildlife is generally a bad idea, no matter what the species or where you are,” says Fleegle.

Wild animals are not pets

Anyone who has ever seen a raccoon nibbling on some peanut butter knows the animals can look every bit as cute and cuddly as a family pet. But all wild animals, even the small ones, are capable of inflicting harm.

In fact, food-seeking squirrels bite more people than any other animal in Grand Canyon National Park. (Related: “How to stay safe around wild animals”)

Providing a buffet for wildlife also teaches those animals to associate humans with food. This can make them more likely to get hit by cars, get into altercations with children or pets, and ultimately, have to be put down by wildlife managers.

This is why experts often say, “A fed bear is a dead bear.” (Here's why feeding bears is worse than you think.)

Junk food

Nutrition is another important factor to consider when deciding whether or not to feed wildlife.

Animals will often make use of a reliable or easy food source even if it isn’t one that suits their nutritional needs. For instance, feeding deer a lot of corn can disrupt the natural balance of acid in the animals’ stomachs and lead to a condition called lactic acidosis, or grain overload.

“This condition has been documented as a cause of death in both deer and elk in Pennsylvania,” says Fleegle.

Feeding can also alter the ways animals move throughout a landscape, affecting distribution patterns. More animals in one spot can also lead to more fighting and injuries, says Fleegle.

What about birdfeeders?

While it may seem like common sense not to feed a grizzly or an alligator, the question of whether to feed backyard birds is a bit trickier. Especially since food put out for birds can also attract many other creatures.

Just like any other kind of food station, birdfeeders can be culprits in spreading of disease, says Kate Plummer, a research ecologist at the British Trust for Ornithology. Especially if they aren’t kept clean.

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Birdfeeders can attract squirrels and other unwanted animals.

For instance, a disease known as trichomonosis has killed millions of birds and caused the United Kingdom’s greenfinch population to decline by around 60 percent since 2006, says Plummer.

But birdfeeders can also be a boon for biodiversity.

In a study recently published in the journal Nature Communications, Plummer found that people are seeing a more diverse array of bird species in backyards now than they did in the 1970s. And this change has coincided with the evolution of the birdfeeder market.

Where people might have once used simply corn or sunflower seeds, there's now suet, mealworms, and fat balls, rapeseed and sorghum and white proso millet, and each supports different species.

“It’s the first time really that we’ve seen this quite obvious, large-scale impact of what we’re doing in our own backyards and how that’s affecting the composition of the birds that we see around us,” says Plummer. “It's quite profound.”

It’s also important to consider that many of these species would have lived in woodlands and farmlands—places that have increasingly been turned into human developments.

“So these birds are finding what they need to survive in our gardens and in our feeders now,” says Plummer.