Off the top of your head, where would you say is the closest wild alligator to you? Quickly now—Googling the answer is cheating. Most people think of gators as creatures of Florida and perhaps Louisiana, not realizing that they are common to the west well into Texas. To the north, we may imagine that they stop somewhere around Disney World. But, in fact, they already range a long way up from Florida. And depending on where you live, global warming could be moving alligators into your backyard.
A few days ago I looked a wild alligator right in the eye from only a few yards away, and it stared right back at me. I felt a sense of communicating with something that was not only from a different world but from a different time. What we were communicating was mostly a mutual sense of wanting to eat each other, but that is beside the point. The thing that really matters was that I could have been peering back into the Jurassic Era through this animal that would not have looked out of place alongside an early dinosaur.
Some of the 200-million-year-old ancestors of modern alligators were very similar to the gators of today. These early archosaurs evolved in a warm world that allowed the cold-blooded creatures to expand across the land and shallow seas of its time.
Alligators are hemmed in to a narrower band of habitat today. The northernmost point of their range in the wild is traditionally thought to be in North Carolina, about a dozen miles from the border with Virginia. But it wouldn’t take much of a temperature shift to allow them to move north. In fact, they have probably already slunk into the Commonwealth.
Three temperatures restrict the range of alligators. First, if the temperature of an egg drops to about 86 degrees Fahrenheit or lower during the first week of incubation, it will be female. Normally the temperature varies in a nest, and some hatchlings are male while others are female. (In mammals, sex is usually determined by which sex chromosome is in the sperm that fertilizes an egg. In many reptile species, however, embryos can develop into either males or females depending on environmental conditions.) If the ambient temperature is too low, then all of the alligator offspring will be female, which doesn’t make for much of a breeding population in the long run. A climate that produces temperatures in this range could support a temporary boom in baby alligator numbers if a few mature adults move into the area and start reproducing, but population growth will halt if the old migrant males die and aren’t replaced by young males.
A prolonged drop below 80 degrees will result in eggs that don’t develop at all. Mother gators can help regulate the temperature of their eggs by piling vegetation on top of their nest to produce heat through composting. But alligators still need warm air in the late spring to maintain an egg-friendly temperature.
Finally, there is the matter of where an alligator can survive, reproduction aside. American alligators are more hardy in the face of cold temperatures than are other modern crocodilians, and they can survive far north of where they can reproduce. Their growth slows dramatically in colder areas, but they are able to burrow into the ground and slow down their metabolism when necessary. It is unclear what their limitations are, but some illegally released pets have appeared to do quite well as far north as southern Ohio.