Why would fertilizing the tree have anything to do with the bird?
My hibiscus tree is about 25 years old - typical single red flower type - is permanently in my son's room - i fertilize it frequently & my birds love to make lace out of the leaves & chew the bark - however being Budgies, they don't do more damage than the tree can replace. No problems so far..... I have stones on the soil at the base - did this to discourager my cat & have never changed them - big stones so the plant can breath & the water can evaporate.
I am allergic to it however

- i have to be very careful when trimming it or handling it - that & grass - gives me red welts & itch.