Extension or Conversion ?

I'm not yet interested in going down the expensive lenses road in an endeavour to get closer to my pelican chicks but this may change with more time and experience. A post on  birdphotographers.net seemed to explain the differences well.
"......... both teleconverters and extension tubes allow you to project a bigger version of the image on your sensor, but they do it in different ways. The teleconverter is a lens which bends the light coming from the lens in front, thus magnifiying the image, and you do all this without having to get any closer to the subject. In contrast an extension tube is just that, a tube, and not a lens, and all it does is give you a closer focusing range. So an extension tube allows you to project a bigger image on your sensor but you do this by getting closer to your subject. And of course you can use a teleconverter and an extension tune stacked together. Another difference is that teleconverters, because they are lenses, have the potential to degrade your image whereas, an extension tube is unlikely to do this. Yet another is that at least Nikon and Canon teleconverters will only fit on some types of lenses, whereas extension tubes fit on all lenses as far as I know. 1.4 teleconverters will cut your light in half but a relatively short extension tube does not affect light levels that much.

For macro work, a teleconverter allows the capture of a larger image of your subject from a greater distance than an extension tube would, all other things being equal. This might be useful for subjects like butterflies or frogs which can be skittish. For macro work on flowers that don't move, an extension tube might be a better option, where the utmost image quality is critical............." John Chardine