Does cycling tone your bottom? I do some cycling, but from what I saw in the mirror this morning it isn't doing the trick. Not to self, go further, or up more hills, or both.
I heard somewhere, sometime, that the best sport for butt-toning is acutally fencing. Fighting with swords that is, not stringing barbed wire. I've not the evidence one way of another to judge one way or not.
There is a logic to it, all that leg work must tighten things up nicely. I'd say horse-riding is good, too. Non-riders think you just sit there and do nothing, but a good brisk English-style trot for five minutes or more is one hell of a work out.