Hi, I am a complete newbie at camcorders. I do know a lot about binoculars and telescopes and a bit about photography.

My requirements:
- camcorder for nature observations (birds, scenery, ...)
- optical zoom of at least 40x
- budget maximum : $500 or 350
- lightweight
- not to fragile
- compatible with Mac OS X and Linux (editing tools)
- if I have to choose between a 40x zoom and a 70x zoom, I would choose the one with the best quality at 40x (halfway the 70x zoom)
- do I have to carry a 3 kg tripod with me to shoot stable movies with a 250 gram camcorder
- good light sensitivity (no night shoots, but able to film on a very cloudy day)
- ability to connect external mic
- good sound recording (meaning for that price range)

Some camcorders in the price range:
Canon LEGRIA FS200 SD Camcorder (40x)
Sony DCR-SX31E Memorystick Camcorder 8GB (60x)
Sony DCR-SX50E (60x)
Canon Legria FS20 (45x)
Panasonic SDR-H80 Harddisk Camcorder 60 GB (70x)

Some other questions.
These cameras are lightweight, approximately 250 grams, but will I have to carry a 3kg tripod with me to shoot stable videos at maximum zoom? The rule of thumb for binoculars is that the maximum magnification for holding in your hand is 12x and I know a lot of people who can't handle that (I have a 12x50).
As I was looking at the specifics of camcorders I noticed that the larger the optical zoom the cheaper the camcorder. I find this very suspicious.

I don't want to spend too much money. It is for starting with a new hobby. If it works out, I can go for a more expensive and better quality model in a year or two. If there are no camcorders in that price range available for nature observations, so be it. I do not want to shoot movies for National Geographic or Discovery channel. Movies that will look a lot better than the average youtube video is ok.

What doesn't get mentioned in technical specs however is the output format of the movies.

Thanx for your time.