The urban monkeys in New Delhi are so bold they’ll right off your plate. If you’ve spent time in New York, you’ve probably seen . Sydney’s white ibises got the nickname “” for stealing trash and sandwiches.

This brazen behavior isn’t normal for most species in the countryside, yet it shows up in urban wildlife, and not just in these cities.

Studies show that animals living in urban environments around the world . At the same time, these urban animals are losing traits they would need in the wild. This process of urban animals’ behavior becoming more similar is known as “behavioral homogenization,” and it with urbanization.

to understand how humans can help wildlife thrive in an urbanizing world. In a new study, we explore the of these behavior changes for urban wildlife.

What makes animals in cities similar?

Cities, despite their local differences, share many of the same features worldwide: They are warmer than the surrounding countryside, noisy, polluted by light and, most importantly, .

, , and other urban wildlife have learned that people are a source of food. And because people typically don’t harm the animals, city-dwelling animals learn not to fear people.

Cities drive evolution as well. Humans and the changes we’ve brought to cities have led to the survival of bolder animals, and those bolder animals pass on their traits to future generations. In genetics, scientists refer to this as the environment “selecting” for those traits.

It’s not just sandwich-stealing that is more common among city wildlife; urban birds also sound more alike.

Why? Cities are loud and filled with , so those who can effectively communicate in that environment are more likely to survive and pass on those traits.

For example, urban birds may , start singing or at to avoid getting drowned out by low-frequency traffic noise.

Cities select for because that’s what it takes to survive.

Animals may behave similarly in cities because they learn from each other how to exploit novel human food sources. For instance, the have learned to open trash bins. are in a race to outwit humans as urban wildlife managers try to design animal-proof trash bins.

The buildings and bridges in cities become home to , , and other urban dwellers, at the cost of learning to use more natural nesting sites. Roads and culverts .

While rural animals may forage at a variety of places and eat a variety of foods, urban animals may concentrate on where they know they can find food, but they end up eating a potentially unhealthy diet.

Consequences of similar behaviors

The loss of behavioral diversity is happening everywhere that humans . This is worrisome on several levels.

At the population level, behavioral variation may reflect genetic variation. Genetic variation gives species the ability to respond to future environmental change. For example, for animals that have evolved to breed at a specific time of the year, .

Reducing genetic variation leaves populations less able to respond to future changes. In that sense, having genetic variation resembles a diversified investment portfolio: Spreading risk across a variety of stocks and bonds lowers the risk that a single shock will wipe out everything.

Moreover, as animals become tamer, new conflicts between animals and humans may emerge. For instance, there may be more car crashes, animal bites, property damage . Such conflicts cost money and may harm both the animals and humans.

Losing behavioral diversity is also troubling for conservation.

When a species loses behavioral diversity, it loses resilience against future environmental change in the wild, making reintroducing urban animals to the wild harder.

Losing behavioral diversity also risks erasing socially learned, population-specific behaviors, such as local migration routes, foraging techniques, tool-use traditions or .

For example, Australia’s populations have been shrinking and are critically endangered. The isolation of having fewer of their own species around has disrupted normal song-learning behavior, making it harder for male birds to sing attractive songs that help them .

Ultimately, behavioral homogenization is making wildlife in cities such as Los Angeles, Lima, Lagos and Lahore behave in similar ways despite living in different environments and having different evolutionary histories.

Many of these behaviors influence survival and reproduction, so understanding this form of diversity loss is important for successful wildlife conservation, as well as future urban planning.