I'm not sure about the rest of the world, but North America has lots of warblers. They come up north in May to breed, and head back to the Caribbean, Mexico, and South America in September and October.
You really need to be an expert to identify them without their springtime migration breeding colors. They mostly look like the photo, or otherwise nondescript. All around my gardens for the past few weeks.
I know three people who have no trouble with fall warblers. I am completely incompetent. Not very good with female warblers in springtime either. Too many hobbies, and not enuf IQ either (me, not the warblers).
In Spring, they are tiny jewels to look at if you do not have a sore neck. Best places to see them in the Eastern US are Cape May NJ, Central Park in NYC (my day record there in May), and Jamaica Bay Wildlife Refuge (also in NYC). All Atlantic Flyway.