Humans throw away a lot of plastic and other man-made stuff, and birds around the world are using these things in their nests, says the new study.
Birds from different places do this – like seabirds sometimes use fishing nets, ospreys use baler twine, city birds can sometimes use cigarette butts, and blackbirds in Europe use plastic bags.
Scientists say the materials in bird nests can be helpful.
Is it good or bad?
It's hard to say exactly whether it's a good or a bad thing for birds, though.
An interesting example is that cigarette butts keep away parasites that bother baby birds.
Some think harder human-made materials might make these bird nests stronger, and plastic films could keep baby birds warm.
But it's important to know that these materials can also be potentially harmful to birds.
A lead specialist explains that animals use nests to deal with human-made problems, like adding our materials to their nests or finding shelter from the heat.
However, sometimes these materials hurt birds – they can get tangled or eat them by mistake.
So, we need to be careful about how much plastic and other human-made things we throw away.
We have to be careful
Scientists say it's worrying that many bird species are using various human-made materials in their nests because these materials can harm both baby and adult birds.
Also, birds can be great indicators of how much human-made stuff is in the environment.
