Why Are We Still Studying Gorillas? The Value of Long-Term Research of Bwindi Gorillas

Categories: Journal no. 61, Appeal for Donations, Gorilla Groups, Ecology, Behaviour, Uganda, Bwindi, Mountain Gorilla

Mukiza has been observed regularly since his birth in November 1999. These portraits show him in 2004, 2012 and 2018 - when he was the dominant silverback of the Mukiza group. (© Martha M. Robbins/MPI-EVA)

A few years ago, when I was well into my now 30-year career studying gorillas, my father asked me, 'Don't we know enough about gorillas by now?' Instead of getting disgruntled by what a daughter of a mechanical engineer could perceive as a personal affront on the utility of my choice of profession, I realized that was a valid question, not only because he wished I wasn't so far from home so much. Gorillas have been the focus of extensive research since the late 1950s, so after so many decades, is there more to learn? The short answer is yes, long-term research on gorillas is valuable for many reasons.

For any research topic, some questions take a long time to answer, whereas other questions can only be addressed when previous questions are answered (studies build on each other), certain knowledge is attained, or new methods become available. For endangered species, research can be viewed along a continuum of 'pure' research, or research for the sake of increasing our knowledge about something, to 'applied' research that examines topics that relate directly to conservation or management.

In the case of my pure research focus, I am interested in the behavioural ecology of gorillas, which is the study of how animals respond behaviourally to variation in their environments. One of the more fascinating aspects of behavioural ecology, particularly for a socially living species is how the ecology, behaviour, and life history/population dynamics of a species all influence one another. However, studying the behavioural ecology of endangered species requires an understanding of the anthropogenic (human induced) influences on their behavioural ecology, so the two go hand in hand. In other words, conservation would suffer without considering the behavioural ecology of a species, and the behavioural ecology would suffer without understanding the impact of external factors inducing change, including those human induced.

The end result is that attaining a viable population is best achieved by understanding the interactions among human induced and natural changes that influence the behaviour, ecology, and population dynamics of a species. Having a viable population makes it possible to learn more about them. Furthermore, for conservation to be effective, we need what is referred to as 'evidence-based conservation management', or management decisions that are based on knowledge or evidence, rather than best guesses or opinions.

Gorillas live in a variety of habitats across 10 countries in Africa. In 1998, I started a research project on the mountain gorillas of Bwindi Impenetrable National Park, Uganda. At the time, the vast majority of our knowledge about gorillas came from the Karisoke Research Center in Rwanda, which was established in 1967. However, as scientists began to study gorillas elsewhere in the 1980s and 90s, it became obvious that the findings from Karisoke were not always the same in other locations. In fact, Karisoke represents one of the extreme habitats that gorillas occupy and there were many differences between them and mountain gorillas living in Bwindi, only about 30 km away. Because of the wide range of ecological conditions under which gorillas live, we cannot assume that the findings from one study or population are valid for all gorillas.

Short-term studies inform us of many things, but for a long-lived animal such as the gorilla, long-term studies are necessary. Over the past 22 years, we have learned a great deal about the Bwindi mountain gorillas that contribute to their conservation as well as for understanding the diversity of gorillas across Africa. However, there are still many things to learn and we must be vigilant in studying changes over time to ensure a future for gorillas. Here I give just a few examples of research topics that have benefitted from long-term studies on behaviour, feeding ecology, and population dynamics.

Social Behaviour

Gorillas are very social creatures, just like humans. Being social means that life is full of friendships as well as conflicts. Male gorillas compete for the alpha position in groups. Females may have conflicts over where to feed. However, particular gorillas may live in the same social groups for a decade or longer, leading to the question of how they manage their social relationships. We have learned that in Bwindi, there is more competition over fruit resources than other widely distributed food resources, which is different from behaviour in the Virunga mountain gorillas. We have learned that there is a lot of variability in the social relationships among gorillas that may live in the same group for years. People are always fascinated to hear about the dynamic social lives of the gorillas.

The Bwindi mountain gorillas also have been part of a study comparing the occurrence of particular behaviours by gorillas in different populations that can be considered as potential cultural traits, or those that are learned and transmitted to others via social learning. For example, Bwindi gorillas have a unique habit of lightly biting into trees as they climb them, which has not been observed elsewhere. While this may not serve any function, it is indicative of social learning and culture, but to study if gorillas have cultural patterns that are similar to some of those in humans, we need long-term observations of who does it and how often.

Feeding Ecology

From a conservation standpoint, it is important to know what foods the gorillas eat in a particular location and monitor if availability of those foods changes over time. Bwindi gorillas spend about 15 % of their feeding time consuming fruit, which is much more than the Virunga mountain gorillas eat but less than the approximately 30 % of the diet of western gorillas. Not all of the fruits that Bwindi gorillas consume are available every year.

One key concern of climate change is that a change in temperature could lead to changes in fruiting patterns and the ability for certain plants to grow, which could have negative consequences for the gorillas that rely on them. It is also crucial to understand how much habitat gorillas need and if the particular areas they use (home ranges) are stable over time. Together, these factors help us to determine how much habitat is suitable for a particular number of gorillas. We can learn a lot about diet and habitat use from short-term studies, but it is only through long term studies that we can monitor changes in the environment and determine how the gorillas react to such changes.

Life History/Demography

In addition to monitoring the total number of gorillas in a population, it is important to study patterns of births, deaths, and dispersal events between social units. We can learn a lot about the dynamics of a population of group living animals by following individuals that are habituated to humans over the course of their lives. A key finding in studying Bwindi gorillas in the long-term is that the interval between successive births by females is 5 years, compared to only 4 years in the Virunga mountain gorillas. This longer interbirth interval will lead to a slower population growth rate if everything else is constant. We are still trying to understand why there is this difference, with variation in ecological conditions being a likely cause. We have also learned that Bwindi mountain gorillas live in both one-male and multi-male groups, similar to the Virunga mountain gorillas, but differing from western gorillas that live almost exclusively in one-male groups. It takes decades to collect enough data to understand their life history patterns because gorillas take such a long time to reach maturity, have slow reproductive rates, and live for a long time. There are several things that we still cannot say much about conclusively since we need more data, such as the length of dominant male tenures and longevity of the gorillas. For example, Mukiza, a male who was born into one of the research groups in 1999 became a dominant male of his own group in 2016, so he's currently four years into his dominance tenure at age 21. Genetic analysis is underway to confirm if he is the father of the four offspring born during his reign.

Overall, the more than two decades of research on the Bwindi mountain gorillas has shown that they are a unique population of gorillas and warrant protection for their continued survival. The Bwindi Gorilla Project continues to focus on several different aspects of research with the aim to not only further our understanding of the gorillas, but also to contribute to their conservation.

Martha M. Robbins

Ongoing Research on Bwindi Gorillas

Development of gorillas: We are collecting longitudinal data on all gorillas born into the four groups from which we collect behavioural data. This includes measurements of body size and growth taken with a non-invasive photogrammetry method, acquisition of dietary patterns, weaning, and social interactions. This work will help us to understand how gorillas develop social relationships as well as how ecological conditions can influence their patterns of growth and attaining maturity.

Long-term social relationships: To understand a key component of the lives of gorillas, social living, we are conducting long-term analysis on the friendly and aggressive social interactions among individuals. We also collect long-term data on behaviours that are considered potential cultural traits. Information on the social behaviour of gorillas is useful for monitoring if tourism is having a negative effect on the gorillas and provides knowledge that piques people's interest in one of our closest living relatives.

Using areas outside the park and crossing a public road: Bwindi is a small protected area (330 km²) and some of the gorillas will exit the park and crop raid. Also, a public road runs through the area used by the gorilla groups ranging in the north-eastern part of the park. We collect data on the location of these groups and record cases of when these groups leave the park and how frequently they cross the road. This information is very important for guiding park management decisions.

Population dynamics: We work in close collaboration with the Uganda Wildlife Authority to monitor all the habituated gorillas in Bwindi to maintain a database of all births, deaths, and dispersal events. This database goes back to 1992 and currently contains about 350 gorillas. Continuing to assess the birth and mortality rates as well as variables such as group size are important for understanding how the population is changing in size over time.

Support for Research Needed!

Martha Robbins leads a team that has discovered many new aspects of gorilla behaviour and ecology (we reported their results in several Gorilla Journal issues). But there is much more to discover!

The Department of Primatology at the Max Planck Institute of Evolutionary Anthropology is going through a reorganisation following the retirement of the former director and the ongoing efforts to hire a new director. As a result, funding for the research conducted by the department has been greatly reduced for 2021. In order to ensure that the long-term field research on mountain gorillas in Bwindi Impenetrable National Park, Uganda and western gorillas in Loango National Park, Gabon can continue, there is need for additional external funding. The research at both sites contributes to both our scientific understanding of gorillas as well as conservation efforts to protect them.

We want to help Martha Robbins and her team continue their long-term research. With your donation you can support this effort. Along with each donation, please include the reference "MPI".

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