Humans love categorizing things, because that is how we make sense of a world that really isn't meant to make a lot of sense. We like things to be neat and tidy, tucked away in to little boxes together with similar things. This isn't always easy, since any one thing can be similar to a lot of other things in a lot of different ways. Should I put the stegosaurus stamp in my dinosaur collection or in my stamp collection? Life is full of difficult decisions. 


Categorizing animal behavior can be very useful, but it can also trip us up if we're not careful. We'll be returning to this topic in part 3. For now, I want you to be aware of the fact that you are likely categorizing behavior all the time. With that in mind, I want to explore on what basis we can categorize behavior and body language; what kinds of categories we use to describe and think about them.  

Note that the various scientific fields that are focused on studying behavior such as behavior analysis and  ethology all have specific ways of categorizing behavior. The definitions below are not necessarily representative of any of these and are in no way official scientific terms. Rather, they are meant as a way for the reader to familiarize themselves with the concept of behavioral categories. If you want to learn more about how behavior categories are defined and used in different scientific fields, please see the reference section at the bottom of this page. 


Behaviors that look similar

A structural category is when we categorize behaviors together based on physical similarities, to quickly describe behavior that looks more or less similar. My example of tail wagging in dogs in part 2 is an example of a structural category. Another example could be "vocalizing." Vocalizations can be very different and include anything from growls to whistles, clicks, talking and loud screams - but all vocalizations are sounds being emitted by a parrot using it's syrinx and mouth. I could also use narrower categories; "whistles" could be a structural category on it's own. Whistles can sound very differently but all whistles can be easily distinguished from growls or other kinds of vocalizations based on their physical properties. Structural categories are what we mainly focused on when we discussed granularity earlier in this section. We described behavior based on it's observable qualities; how it looks and sounds. To do this we don't need any more information than what we can get from looking at what the parrot is doing. 

Behaviors that have similar effects

A functional category is when we lump behavior together not based on physical similarities, but rather similarities in their function. What effect or consequence does that behavior have for the bird? 

We could define "distancing behavior" as anything a bird does that results in an increased distance to another individual. It could be lunging towards someone, growling, holding a foot up, or flying away. If something the bird does results in more distance to someone else, then it is a distancing behavior according to our definition, no matter what it looks like.
Unlike a structural category, we can not know if a behavior belongs to a functional category by just looking at the behavior itself - we need to observe the behavior in context to see what is happening in the environment the bird is in, and and what happens after; what effect or consequence the behavior has, in order to know what function it has for that individual in that context. It's important to realize that behavior that looks structurally identical can be performed in different contexts, and have different effects on the environment. So behaviors in one structural category can belong to many different functional categories. We'll get back to this in part three. 

...And more. 
There are also categories that are both structural and functional. A contact call is a good example. All contact calls have the same function and all contact calls are structurally similar in that they're all vocalizations. There are behaviors that can have the same function (getting attention) as a contact call without being a vocalization, and there are vocalizations that are not contact calls. 

Sometimes, it can also be useful to group behaviors together based on their evolutionary context. One example is reproductive behavior. This might include everything from regurgitating food to mating and incubating eggs; all behaviors with both different structure and immediate function, but that are all performed with the ultimate effect of- and in the larger context reproduction.  


As mentioned above, there are many more ways to think about and categorize behavior. Hopefully, this short introduction to some of them has made you more mindful about how- and why you group behaviors together when you think about them. We'll be returning to this subject and discussing how the way we categorize behavior can influence how we interpret it, for better and for worse, in part 3.  


Purton A.C., Ethological categories of behaviour and some consequences of their conflation
Animal behavior 1978, 26; 653-670

Examples of categories in behavior analysis (scienceofbehavior.com, ABA glossary)