I think the backgrounds here work better than a plain background when considering the image as a whole. Yes, it may make the main subject a touch more difficult to isolate (though I think the depth of field in these shots is excellent and more than enough to break out the subjects), but these backgrounds put the subjects in context.
If these were meant to be illustrations in a nature guide, sure, maybe you try to get a less busy background (or even shoot them in studio against a black or white backdrop). But for shots taken in nature (not just shots of nature), I like them.