His threat was pretty awesome. yeah. But it was also very blank. First, he clearly wasn't protected from them, they could easily eat him. Second, he was offering them a forest, but what would they do with it if they don't have any food source?
The Doctor might not actually have had anything able to keep them from just eating him - but they don't necessarily know that. They have no way to.
This is the man they have on record as having survived numerous "deaths" before as well as having wiped out entire species. Someone immensely dangerous who keeps to his threats.
So, they evidently just came to the conclusion that it wasn't worth the risk of trying, lest they end up like one of his many, many past foes.
As for the food: Given on Earth they apparently mostly eat road kill (and only the occasional lost human), they apparently don't actually need to eat anywhere near as much as they did at the library. So, it might take a while for that to become an actual issue for them - as opposed to the immediate danger they were presented with then and there.