Forgive me if my thinking is not correct, but is the humming bird not creating lift? Lift has to be equal to the force of gravity on the bird for it to be flying. (unaccelerated flight means the craft, or bird, is in equilibrium) So it is not placing any extra weight on the jar. Just like if a 1600 lbs Cessna skyhawk flys over you head it does not put an extra 1600 lbs on your head to keep it in the air, but if it land on you, you will most certainly be squished.