I've recently spent a lot of time stalking a variety of wildlife including roe deer, brown hare and red fox - so here are a few tips that I've learnt that can make all the difference in getting closer:
1. Research your subject: not all animals have the same senses or see in the same way. Roe Deer for example see in monochrome - their sight is much more sensitive to movement and human outline.
2. Camouflage hoods are great, but it's still worth adding extra camouflage to break up the outline of your head. Stitch in green netting which can be stuffed with various grasses, bracken and even branches to make your head as un-human as possible.
3. Be aware of ground cover. Smaller mammals can be well concealed in summer - so you might need to keep a check with binoculars as you approach to be sure you're not being seen.
4. Stay low. It's hard work but keeping close to ground level is the best way to ensure you're not spotted.
5. Use AV mode so you don't have to worry about changing light as you get closer.
6. Try to use sunny days so you can use faster shutter speeds and hand-hold. Tripods/monopods can be very impractical in stalking situtations.
Hopefully off to try for my local short eared owl again this evening... fingers crossed!!