> in some areas of the Thames, you can create a nesting habitat for an endangered bird on your boat, and then once the bird settles in, they can't force you to move, since doing so would destroy an important habitat.

Seems like the fix for that would be to force you to leave the boat where it is, but to stay off of it so as not to disturb or disrupt the bird's habitat while at the same time leaving you responsible for rent and the boat's upkeep. That way you'd have an expensive boat you can't use but must also pay for and maintain. The plus side being that nobody in their right mind would try to attract endangered birds, the downside being that in order to avoid the costs, a cruel person might harm the bird if it happened to build a nest on their boat naturally (not sure how often that actually happens when people aren't intentionally building habitats for them).

It's possible that discouraging that kind of thing just isn't worth it. Maybe the people taking up space with their houseboats aren't as big a problem as there not being enough nice habitats for a struggling species, and the loophole is a net good for the restoration of the bird population without being a major problem for others.