The Osprey is a rather anomalous bird, as it usually spends the winter in Africa and breeds in the north of Europe. But in Italy some birds have learnt to spend the winter (in Sardinia only, I believe) instead of migrating south, while the youngest ones who do not feel up to breeding will sometimes spend the summer in Sardinia ("estivando") without, however, attempting to reproduce.

So bear in mind that these are two completely different terms.

As you have probably guessed, I am an ornithologist by passion!