To add to what BP said, feral hogs can start breeding at 7-8 months of age and will produce 2-3 litters of an average of about 4-6 individuals per year, although have been recorded over 10 in good conditions. Survivorship of the young is fairly high because of a combination of protection of being in a sounder (often extended familial and co-familial groups), being able to be fed by multiple sows, and a very limited number of natural predators outside of humans. Bears, alligators, crocodiles (limited to southern tip of Florida), wolves, and mountain lions are pretty much all there is in North America that poses as a natural threat.
The notion of hogs being "released" into the wild got me to do a little historical study sometime back, in part because of stories my father recounted to me of raising pigs in east Texas. The practice he described was one I found documented back to Jamestown and universally practiced across the US. It is the practice of free-ranging the livestock. My father would turn out the hogs in the morning and in the evening have to rustle them up from the bottoms and bring them back home. Not all came home. Sometimes, he would end up with neighbor pigs and vice versa. The pigs didn't care whose home they went to. All they knew is that they were going to get slopped at the end of the day, hence their willingness to return home.
Free ranging was one of the best ways to raise pigs. Why? The pigs fed on their own from nature during the day, watered themselves, and deposited their waste away from humans. It also meant keeping even small groups genetically diversified as they met up with other groups and bred with them during free ranging activities. As noted with not all the pigs coming home and sometimes ending up with the neighbor's pigs, free-ranging also meant hogs were continually going wayward. Some went feral.
Here is a neat reference about Jamestown and the folks there nearly being overrun with feral hogs as a result of this practice.
http://books.google.com/books?id=aG...AQ#v=onepage&q=jamestown overrun hogs&f=false
Unlike deer, BerdanSS, hogs are omnivores. They do hunt. They scavenge, even cannibalistically. They eat plants. They eat mold. They eat fungus. Their rooting activities create erosion problems and often kill the plants under which they are rooting even when the hog isn't consuming the plant.
(good usable food too, not saying it's got nothing to do with that anymore obviously) point being, I wouldn't want to see any huntable species GONE. What's wrong with low, controlled numbers?
