(do something) little by little

Use the phrase "little by little" to describe something that happens slowly. Another way to say this is "gradually", but "gradually" is more formal. "Little by little" can be used for both positive and negative things:

We're starting to get the hang of it little by little.

She's losing her memory little by little. Soon we're going to have to move her into a nursing home.

There are actually a lot of phrases like this that express doing something slowly and steadily. Here are a few:

bit by bit

inch by inch

day by day

one by one

(an animal's) natural habitat is being destroyed

An animal species' "natural habitat" is the area and environment that the animal usually lives in. For example, some animals live in rainforests, others live in grassy plains, others live in deep ocean waters, and so on.

These days, a lot of animal species are in danger because humans are destroying the animals' natural habitats. This happens when people build homes and farms, release pollution, and so on.