First of all: Thanks to everybody for the quick answers!
saraf wrote:
How heavy is your lens? Can you walk for 3-4 hours at a time with it around your neck?
Personally I wouldn't risk my dSLR but then I'm a clumsy oaf and likely to trip over.
It's a Canon EOS 400D body (500g) + 75-300mm IS (630 g) + Battery Grip (ca. 150 g) + Batteries (ca. 50 g) => Total is about 1,3 kg. Pretty heavy

, thus I didn't intend to carry it around my neck, just in a shoulder bag or little backpack.
The advantage of this combination is:
the 70-300mm lens image stabilizer is
pretty effective and walking in the morning gets some nice moody pictures - hopefully. The sound of this lens won't be a noise problem, because it has an ultrasound motor.
Disadvantage: Very heavy and might get full of dust when walking. No videos at all (too old camera)
The only problem might be the shutter noise - as described above. Two years ago an elephant heard my shutter ca. 200 m away from me and moved towards our car but fortunately walked away soon afterwards. Pretty scary when not in a car and the only way of hiding is behind a

ranger.
The other camera is an old Fujifilm S5500 (f 2.8-3.1), "only" 4 MPixel,
no image stabilizer, but still a very smart camera becaues the lense is totally covered by an extra tube, on which I've got an UV or Pol-Filter. So no dusk at all!!! And as described above, the noise can be neglected - except the starting of the camera, when the lens gets out of the body. Further advantage: Videos (though only 640x320 pixels)
Disadvantage: Internal Battery forgets time and date every now and then. Resetting makes a lot of noise until I switch of the sounds.
The last alternative is an Canon Digital Ixus 120: Advantage: Very small, HD-videos in excellent quality. But again: No considerable zoom and vulnerable to dust.
You see, I'm pretty desperate.