HI Robert
There is a trade off between fast shutter speed to stop motion and depth of field to keep all of the bird in focus and speed of film "ISO from 100/ 1600" depending on your camera to not introduce noise and still have enough light.
That said I try to keep my ISO around 200/400 on my D2X which seems to need more light than my D100, enabling me to keep a little more DOF which keeps more of the bird in focus.Do you use manual setting or all automatic. If you are prefocusing try to imagine where the eye is in relation to his perch. If you can give him a perching place where he will want to land just prior to his feeding spot , where he can hop down to. Having good natural light also helps. Keep your shutter speed above 250 if possible, titmice and chickadee's and others have real quick darting movements and the speed helps eliminate that. What kind of camera/lens do you use, give us more info and we can help more .

thanks for sharing hope this helps Randall