Oil level changes when engine warms up is this normal?

I have a 2002 Honda 450 Foreman. When the engine is cold, when I check the oil, it reads full, at the upper marking on dipstick. After I run the the atv for a few min, I check the oil again and it reads between the low and full oil level marks. So it reads lower after engine is warmed up. Is this normal? If so, when should Oil level be accurate, cold or warm engine? Thanks