Question

Is the answer previously,as a result, in contrast, or for instance??!

Answer 1

The answer would be for instance.

It would be this answer because after stating that cuckoo birds can look like other birds, they give an example on how.

Whenever the phrase for instance is used, it is usually to give an example.

Answer 2

The answer is for instance. This is the answer because the term "for instance" is sometimes used to give an example. In the paragraph, for instance is used to give an example of how cuckoos mimic other animals.