Well I tell you what. We raised some pigs a few years ago. They ate just about anything and everything that we gave them, EXCEPT citrus fruits. Even when I throw them to the chickens they basically ignore them. So you'll probably be safe where you are at. Deer won't touch the fruit, I'm sure, they don't like the smell.

We can't suggest solutions for an unknown situation. Do you know what tulle is? Might be worth draping your plant with it or constructing a small frame on which to staple the fabric. It will kerp birds out.

Some may have other information but I have always been comfortable eating fruit that was not fermented. Citrus has sections so the bird may have caused some damage to one or two sections but I'm guessing the damage goes little deeper than the rind. I say pick your first lemon, slice off just the skin at the deepest damaged place to better determine how deep the damage is and enjoy the rest! I also have bird problems with my Ponderosa lemons. Boat-tail grackles come in about this time of year and they don't peck holes in the peel but they scrape off the green zest. The lemons still fill out and mature but they are deformed because of the damage to the outter skin. I haven't found any ways to keep the grackles at bay.

BT is Ok since it only affects caterpillars. I personally don't use poisons of any kind on anything I'm going to eat. I use a good spray of water for things too small to pick off and toss to the birds.