The light here is almost a constant grey, yesterday was no exception I tend to shot an high ISO 800 or more just to get decent shutter speed a must for small birds, plus the DOF has to at least 6.0 more some times as otherwise focus is only achieved on part of the subject. I enabled the noise reduction for ISO in the cameras menu. I also find noise is better with a greater distance between the subject and backdrop. You can also draw birds and mammals into a suitable area in its habitat by feeding calling or getting on flight paths and runs as said in ealier in the thread understand habits routines of the intended subject.
Regards
Colin
40D + 300mm 800 ISO @ F8 freehand