Animals have active periods that span from the time they wake up to the time they go back to sleep. Chimpanzees are diurnal, meaning they're mostly active during the day. The way they allocate their time from sunup to sundown is called an activity budget. At the most basic level, can be divided into time spent resting, traveling, feeding, and socializing. Activity budgets are different for different species. Some need to spend more time feeding, others more time resting, or watching out for predators. They also vary within species often by sex, reproductive status, or even individual. For example, we know that males apportion their time differently than do females and that females nursing offspring, behave differently than females that are mating. As scientists, we're interested in studying activity budgets, because we want to understand the choices that animals make and how they have evolved. These aren't rational conscious decisions like we humans make every day about what to eat and where to go. Instead, these are strategies that have evolved over time. Individuals that budget their time and energy in the most efficient or optimal way are the most successful. So what does this look like in practice? How do we build an activity budget? Say you're in Gombe and interested in the behavior of female chimps. You pick a focal subject, one animal you'll follow all day recording her behavior. Every five minutes you record what she's doing according to predefined categories. At 9:00 AM, she's traveling, at 9:05 she's resting, at 9:10, she's eating some fruit and that tree, which she is still doing at 9:15. You record these little snapshots every five minutes all day. The next day you pick a different focal subject. You collect the same kinds of information according to the same protocol. Over days, weeks, and months of data collection, you can start to look for patterns. You can tally up the total time that you spent observing females and find the total number of instances in which you recorded them doing particular behaviors. This data collection and analysis is pretty simple, but it starts to paint a picture of the way your study subjects spend their time. The question that you ask will determine how specific your behavioral categories will be. Think for a minute about your own behavior over the course of a day. You may have taken a nap, sat on a bench for a few minutes, and also watched some television. All of these activities could be considered resting. In contrast to the time you spent taking a walk and riding your bicycle, both of which could be considered traveling. For some questions, the broader categories of resting and travel will be sufficient, while other times you may wish to compare time spent riding a bicycle between two groups of people. So you will want to use more specific definitions of travel. It's the same for chimpanzees. For instance, climbing, running, and walking can be lumped into a travel category or compared separately. More specific categories are frequently used when examining time chimpanzees spend socializing. Grooming, playing, and fighting, are all social behaviors but are usually examined separately because these behaviors occur under very different circumstances. We can go beyond simply describing how they spend their time. We make and test hypotheses about factors that may influence activity budgets. For example, pregnant and nursing females may have different priorities than females who are mating. A study of chimpanzees in the Mahale mountains found just that. Females there spend more of their time traveling when they are ready to mate, leaving less time for feeding, grooming, and resting. At Gombe, we investigated differences between activity budgets of males and females during a two year period between 2013 and 2015. We used the broad categories of travel, rest, and feed but differentiated between social grooming and self grooming. Here's what we found. Males are on the left and females on the right. The larger the size of pie, the more time spent in that behavior. Overall, the activity budgets of males and females are pretty similar in this sample. However, males spend more time grooming with a partner while females spend more time grooming themselves. This makes sense, since males are the more social sex. Often researchers have an impression of what is going on even before we crunch the numbers. For instance, anyone who has spent many months following chimpanzees around the forest, could tell you that they rest at mid day to avoid the hot sun. One study in the Budongo forest in Uganda, supported this impression. Temperature affected activity, chimpanzees spend more time resting on the ground during the hottest parts of the day. Researchers experience and understanding are definitely important. But by testing carefully across large amounts of data, we can confirm or refute our hypothesis.
