Everyone knows what it feels like when their personal space gets invaded. When somebody gets too close to me, it makes me so uncomfortable that I’m almost compelled to step back and gain some distance from the other person. Just a precious few steps make a huge difference. Being from New York, perhaps I’m particularly sensitive. The amount of space a person needs is influenced largely by cultural factors; I have a few international friends who tend not to follow the same guidelines as I do. Often when interacting with them I’ll have to remind myself that they aren’t trying to determine what it takes to get punched out while I politely find some excuse to move behind a nearby chair or desk.
Many animals, typically mammals such as wolves, also like to keep some space between themselves and others. When this occurs, we tend to say the species is territorial. But although the term is often used casually, as in when referring to a neighborhood dog, it is anything but an abstract notion.
As with any biological concept, our ideas about territoriality have been refined over many years as result of scientific research, pontificating on conjectures, and arguments during scientific meetings. As a result of this debate, a specific set of conditions have been formulated to define when it is justified to characterize a species as territorial. First of all, an animal must have a territory that stays in the same place over time. So, a dog that strolls around randomly, snarling at anyone they come across isn’t territorial. Second, they must exhibit some sort of behavior that results in other animals of the same species avoiding the area. Most people probably think of bears fighting or bighorn sheep ramming heads in efforts to persuade each other to scram, both purely physical strategies. But there are more subtle methods of establishing one’s territory as well. In the animal world, scent may be the most important sense and it’s used often to dissuade others from coming too close. Think of the stray cats you’ve had strolling around in the middle of the night, they’re not just yowling, they’re spraying urine all over your house. It’s all in an attempt to keep other male cats from coming too close. So, the next time your house smells like cat pee, don’t get upset. At least there aren’t two cats prowling around.
Finally, the third condition is that through this behavior (physical or otherwise) their territory becomes an exclusive area. In other words, before an animal may be considered territorial, it must be shown that they have a specific space that they reside in by themselves only by keeping others from entering. An unfriendly dog that growls at any other dog isn’t territorial. A dog that keeps other dogs from entering its yard is. In the wild, a territory isn’t as clearly defined as a backyard, but still, animals including bobcats, coyotes, wolves, and bears defend spaces with borders known only to them. Many birds defend territories by singing (or hooting). Their sounds are often enough to persuade other birds from coming too close. Some fish species become territorial only during the mating season, forming a small territory around a nest site and chasing other fish away.
Many lizards are known to be especially territorial, they do push ups and display their colorful throats in an attempt to scare off other males (and attract females in the process) and, if that doesn’t work, they’ll fight. Interestingly, although snakes are closely related, none are known to be territorial.
I recently completed a radio-telemetry study of kingsnakes, Lampropeltis getula, wherein we implanted transmitters inside a dozen snakes and used an antenna to track them down and find out where they went. The original goal of the study was to determine how much space kingsnakes used and which habitats they prefer. But, sitting in front of the computer after the study was over, I noticed that when you traced an outline around all of the places we found a particular snake, they rarely overlapped with the outlines generated by other snakes. It was almost as if each outline was a piece of a jigsaw puzzle across the landscape. This was intriguing.
Scientists often lack the ability to research the fine points of territoriality. It’s hard to know what an animal is thinking when it’s fighting, or singing, or doing pushups. Are they acting territorial? Or maybe they’re just cranky. Instead, researchers typically focus on studying the space that an animal uses (often referred to as a home range) and then making inferences about territoriality. One of the most common methods used is to identify the region an animal patrols and then determine how much of that area overlaps with another animal’s home range.
Scientists have determined many mammals are territorial by demonstrating limited overlap between home ranges. But when I showed that kingsnakes also had low overlap, many found it hard to believe that these animals were territorial as well. There just weren’t other compelling lines of evidence to suggest they fulfilled the criteria I note above (even though they are known to fight and eat each other). My findings were eventually accepted for publication, but I had to stress that what I found was only consistent with territoriality and did not definitively state that kingsnakes were territorial. But, I still think my results were interesting. They either are the first to document territoriality in a snake or, on the other hand, effectively demonstrate that examining space use alone is not an accurate way of determining territoriality in any animal.