Animal Forecast

Alligators in Your Backyard

Thanks to climate change, the cold-blooded giants are lurching north.

Guess who's coming to dinner?
Guess who’s coming to dinner?

Photo by Al Messerschmidt/WireImage/Getty Images

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.

As average annual temperatures have increased in recent years, the zone in which alligators could plausibly both survive and reproduce has moved north. With the northernmost known population of gators so close to Virginia in the first place, it wouldn’t take much to get them established in a completely new state. Some locals already report sightings in the vicinity of Back Bay, southwest of Virginia Beach. Officially, there are no alligators in Virginia. But in practice, I don’t think the alligators have paid attention.

Last year, I put the word out that I was interested in alligator sightings within Virginia, and I was showered with emails reporting gators seen and in some cases even killed. Even the official, fully documented cases have been marching steadily north. There is little question that a grown alligator was documented only 5 miles from the Virginia border in 2011. Odds are that the species is now here in my home state. The question is how many of them have arrived and whether the spring temperatures are high enough to allow them to breed.

Arguing against the concept of global warming has become an exercise in absurdity. Last year was the warmest year on record in the Lower 48 states, and the weather is becoming hotter on the whole. This temperature shift has ecological consequences that tend to favor cold-blooded wildlife. The American alligator, the venomous cottonmouth snake, and the Carolina anole each find the northern limit of their range right around the Virginia/North Carolina border. All can now expand their ranges.

Virginia biologist and blogger Kirk Mantay pointed out to me that just because an animal can move to a new habitat doesn’t mean that it will do so right away. Alligators won’t necessarily pour into Virginia; their movement will be gradual. First, you must have some gators that are unsatisfied with where they live or that have been pushed out of their previous territories by competition with other gators. Those alligators in dispersal will move outward and stop when they arrive in an area where there is plenty of food. It could take a decade until there are so many gators in the Old Dominion that it is no longer possible to deny their presence.

Yet odds are that alligators will be denied for as long as possible. Every government agency involved in monitoring or regulating wildlife in Virginia has a strong incentive to claim that alligators aren’t here. For what is to gain? As Mantay put it: “Once any (or each) agency acknowledges that the species exists in the state, then broad actions have to be taken to assess it.” He points out that government agencies would have to decide whether the species should be considered invasive in Virginia, endangered, or something else altogether. “Real plans, with real biologists, would have to be put in place, per state and federal laws. That will cost lots and lots of money.” It’s much easier to claim that every wild alligator spotted in Virginia is either a figment of someone’s imagination or an escaped pet.

It is impossible to precisely predict how far north the American alligator could spread. That will depend in part on how out of control global warming becomes. Perhaps their move will stop near the city of Virginia Beach, in the area where the animals are probably already living. But if temperatures climb high enough, vagabond gators could start cruising toward the James and Potomac rivers a few decades from now. Washington, D.C., is only about 150 miles away, as the crow flies, though longer as the gator might swim.

This expansion into Virginia is probably more historic to humans than it is to alligators. Gators and their ancestors have moved up and down what is now the mid-Atlantic coast many times over millions of years as the climate has warmed and cooled. So far, the current shift is modest by historical standards. But if the trend keeps going, then New York City had better keep an eye on its sewers.