I have taken two nilgai with my 65# Wes Wallace recurve. We hunted free-range animals in south Texas. There are about 40,000 of them in a four county area. The vast majorities are on the King or Kennedy Ranches. It is some of the best eating I have had. My wife always ask when I plan to hunt them again. They were transplanted from India and have found that the south Texas climate is conducive to there reproduction in the wild. You will find the dung piles, which to me just means they are in the area, but it does not necessarily mean that they will frequent during daylight. The mature bulls are very aggressive and have been know to kill each other as well as domestic cattle during the “rut.” I use the term rut loosely because they tend to have kind of a rut or breeding season in January and February, but can breed almost any time. So this time of year I tend to see more movement as the bulls are looking for cows. Water holes are a good start in Texas because it is dry. I am not sure if you will have the same localized pattern in Florida if there is access to excessive water. We had reasonable success stalking because we did see more animals and focused our attention on the transmission areas between mesquite and live oak. However, a tree stand in the transition zone was most productive. Their natural predator are tigers, which are usually on the ground, so getting into the trees helped us get around their awesome vision. Food was really everywhere, so yes it did make it difficult to pattern them. I do not know of any bait you could use to bring them in.
All of this may be interesting to you, but none of it may be relevant in Florida. I image that these will be captive animals, but I am not sure. As far as them being tough to kill, this is true. Mainly because there heart and lung set forward in their thoracic cavity a little more than deer. I would check out the anatomy of other plains antelope as well to get a reference. They also have a high hump between the shoulders due to extremely long spinal process of the vertebrae. This gives you an illusion of a large target, when actually you should be aiming quite low and forward just above where the front leg connects to the body. Look only for broad side or slightly quartering away shot. From a tree stand it becomes even more difficult since most of us are used to shooting deer and we can hit them higher. The bigger bulls develop tough hide in their front shoulders due to fighting. Another thing about nilgai that makes them tough is they can run very fast and cover a lot of ground, so even a good fatal hit may leave you with a much greater distance between blood drops. Their hair is thin and lays flat. They cannot handle the cold very well. There has been several die-off due to extended uncharacteristic freezing weather in south Texas. The challenge is great, but so is the reward if you are truly able to hunt them.
I published an article about nilgai in TBM, you may be able to read it in the Best of Traditional Bowhunter book compiled by Gene Wensel. brothersofthebow.com
Good luck and have fun,
Mike