What was found
IMMEDIATELY AFTER TAKEOFF FROM ILN, NR 3 FIRE WARNING LIGHT AND BELL CAME ON. AFTER APPROXIMATELY 5 SECONDS, THEN LIGHT WENT OUT. FIRE WARNING TESTED GOOD. SECURED NR 3 ENGINE AND LANDED. POSITIVE OIL PRESSURE INDICATED. FOUND CHARRED BIRD NEST NEXT TO AFT BOTTOM FIRE LOOP. CLEANED REMAINING NEST FROM COWLING. REMOVED AND INSPECTED NR 3 ENGINE MAIN OIL FILTER, CHECKED GOOD. PERFORMED GROUND RUN. LEAK CHECKED GOOD.