United Kingdom 
I have a small sunflower with three lovely buds and one flower fully out.
Today, I have found it uprooted and totally decimated! All the stems have been stripped and every flower head has been chewed at the base and is just hanging. Also the back of the open flower has been attacked. There is no sign of slugs or slime or aphids.I have now put it in a pot to see if it will revive, but I think it may be too far gone.
We do have Pheasants visiting our garden, and know they occasionally peck at leaves. Do they like sunflowers? Are they likely to be responsible for this decimation?
Thank you
3 Aug, 2015
Answers
Uprooted sounds like a larger animal to me, such as a deer or hare.
5 Aug, 2015
Previous question
Looks like slugs or snails to me. They like to chew through stems and the leaf in your photo looks very much like snail damage.
3 Aug, 2015