Different DSLR models have varying numbers and arrangements of AF points. In theory, more points are better, but not all cameras have powerful enough processors to deal with all AF points quickly enough for really difficult subjects like birds in flight. Also, busy backgrounds, such as foliage, can confuse multi-point AF and cause it to focus on something other than the desired subject. The number of AF points is only part of the story. The entire AF system needs to be considered. More up-to-date AF systems with fewer AF points and more powerful internal processors can outperform older systems with more AF points. I use multi-point AF only when a bird is flying against a plain background like a clear sky, and just the center AF point otherwise. For portraits of stationary wildlife, you can activate the AF point over the eye nearest the camera. Experiment with your camera's different AF-point options to see which work best for you and your gear.
The lens plays a big part in AF performance, too, of course. The pro supertelephotos—300mm ƒ/2.8, 400mm ƒ/2.8, 500mm ƒ/4, 600mm ƒ/4 and 800mm ƒ/5.6—have better focusing motors and AF algorithms, as well as better optics than lower-end lenses. They're more rugged, with better sealing against weather and dust. They also cost a lot more, and are much bulkier than lesser lenses, but they're really that much better.
Many photographers are unaware that their AF systems operate with the lens wide open at its maximum aperture. As the shutter button is pressed, the lens iris closes down to the chosen ƒ-stop an instant before the shutter opens and the exposure is made. Most AF systems can only operate at ƒ/5.6 and greater apertures. Because many wildlife photographers use teleconverters to extend their focal lengths, a DSLR with an AF system that works down to ƒ/8 is preferable.
EVF DSLRs For Wildlife Sony's SLT cameras offer some unique advantages for wildlife photographers because they can provide continuous phase-detection AF in Live View mode, including videos. A nonmoving semitranslucent mirror and an eye-level electronic viewfinder replace the typical DSLR's moving mirror, focusing screen and optical viewfinder. The semitranslucent mirror transmits most of the light to the image sensor and a portion to the phase-detection AF unit, so you get full-time continuous AF, with convenient eye-level viewing, even for movies. Thus, SLT cameras can do videos of birds in flight. (When conventional DSLRs are in Live View or Movie mode, the eye-level finder blacks out so you have to use the external LCD, and the phase-detection AF doesn't work, so the camera has to switch to contrast-based AF, which is too slow for action as implemented in DSLRs.)
If you want to capture wildlife action videos as well as still shots, you should check out the SLT cameras and see how you like the EVF.