"aren't many things you can do by yourself that burn calories as well as running."
All activity's at your aerobic limit burn the same number of calories. You can run, dance, row, weigh lift, or just bail hay, and you will encounter the same limit. It's basically a question of how much oxygen you can absorb though the lungs and dump into your blood stream.
That's true, but you have to work pretty hard on a bike to get your pulse rate as high as you do by running. (I've done a fair bit of cycling and running over the years). For an inexperienced cyclist, tired leg muscles tend to limit the effort before their heart and lungs do. And it's always tempting to take a rest on the downhills. So I reckon in most cases, you burn significantly fewer calories per hour cycling than you do running. On the other hand most people are capable of cycling for say two hours (if they have time) whereas it takes a lot of training to be able to run for two hours.
It's also a question of motivation. I'm sure I burn more calories mountain biking given the fact that several times I've gotten to the top of a hill and then puked. I've never pushed myself that hard running.
All activity's at your aerobic limit burn the same number of calories. You can run, dance, row, weigh lift, or just bail hay, and you will encounter the same limit. It's basically a question of how much oxygen you can absorb though the lungs and dump into your blood stream.