What exactly are they doing to the bamboo, WW? Are they shredding the leaves for nesting material? Maybe you can set out some raffia or shredded magazines, as an easier substitute.

welcome to GoY.
have you seen the birds shredding the leaves? some of mine have been shredded by the wind.
how tall are your bamboos? you could try stringing fine thread around the plant but offering alternative materials is the best option.