DURING A CARGO FLIGHT, THE PILOT WAS FLYING THE AIRPLANE AT ABOUT 500 FT AGL UNDER AN OVERCAST LAYER. A FLOCK OF BIRDS FLEW INTO THE AIRPLANE'S FLIGHT PATH AND THE PILOT TOOK EVASIVE ACTION TO AVOID A COLLISION. AS HE ATTEMPTED TO RESUME NORMAL FLIGHT, THE AIRPLANE WAS IN CLOSE PROXIMITY TO THE TERRAIN. SUBSEQUENTLY, THE VERTICAL STABILIZER COLLIDED WITH A TRANSMISSION WIRE THAT WAS STRETCHED ACROSS A SHALLOW CANYON. THE AIRPLANE YAWED VIOLENTLY, BUT THE PILOT WAS ABLE TO MAINTAIN CONTROL AND LAND AT A NEARBY AIRPORT.