As awful as this sounds, I think it might be easier to train crows to pick up people's trash than to train people how to throw away their trash. People are apparently not as easily teachable as literal birdbrains.

Using people to pick up trash and throw them properly is the solution that has been used for centuries. Crows are paid peanuts (literally) for bringing back trash. They are employees.

And I am sure that if you were to offer people a dollar as a reward each time they bring back a trash to a trashcan, the parks would be clean.

In Berlin glass bottles are reused and there is a reward for bringing them back to specific bins. I have seen homeless people looking for trash and filling carts of these.

That reward as you call it, has created a 2nd level economy in Germany.

It is not only homeless, people with very low pensions or not able to get a proper full time job also hunt for them, everywhere.

On the streets, trains, subway, beach, lakes, you name it.

To the point that many people don't throw away bottles anymore, leaving them grouped outside the trash cans, as means to help those people pick them without messing with trash.

There are even trash cans in the Rhein region that have bottle holders around them.

So yeah it helps keep the street clean from bottles, but fighting the causes of this 2nd level economy would probably be a better idea.

What is the correct word for the reward? That's one of this weird case where I know the word in French and German but not English...

Our public waste bins are designed like this in Vancouver. People put bottles/cans with deposits in a circular metal holder below the rim of the trash bin so that the homeless can pick them up easily. There are a LOT of homeless here. I moved back to Canada from Central America and my first impression of being back in the developed world is my god look at all the homelessness.

That happens in San Francisco, too. You'll on occasion even see someone on the local public transit with a big trash bag full of bottles. I guess they're on their way to a redemption center for the deposit.

I don't know. Have we tried giving a tasty nugget of bird food too to every human who uses the bin?

A lot of the litter I see is thrown from cars. I can't imagine the people who throw cigarette butts and trash out of their car windows driving around to find a bin for a nugget.

I think the people that throw trash from cars are EXACTLY the kind of people that would hunt down a nugget bin, but then get really pissy and entitled when it out of dipping sauce.

Well, in Japan, littering is rarely seen.

More like teaching all the people to deal with their trash with perfect reliability is harder than teaching literal bird brains to pick up the trash that the humans haven't dealt with. If only half the crows get it, that's probably enough. Only half of the humans would be a catastrophe!

As a reminder, this is what you end up with when everybody litters where they want and nobody picks up the trash:

https://www.bing.com/images/search?q=trash+in+Indian+cities

I'm more concerned that the crows get a little too aggressive about it and try to pick up things from people's hands.