Studying the Gorillas' Move

By Dr. Charles Ritzler

Dr. Charles Ritzler is an animal welfare scientist in the Animal Health and Welfare department at Brookfield Zoo Chicago. With previous experience observing western lowland gorillas, Dr. Ritzler’s behavioral research and innovative study of habitat design’s effect on animal welfare help Brookfield Zoo Chicago better care for the primates at Bramsen Tropical Forests (among other animals)!

“How are the gorillas doing in their new habitat?” is a common question asked along the pathways of Bramsen Tropical Forests since our grand opening on July 11 of this year.  

This question has also been top-of-mind for the Brookfield Zoo Chicago team! Our animal welfare science team, working closely with animal care programs, has been conducting a long-term study focused on how exactly the gorillas are adapting to their new spaces.  

Day One: opening the Habitat Doors to Bramsen Tropical Forests

Just over one week before opening to the public, the shift doors were opened for the first time, and the gorilla family group was able to access the outdoor habitats of Bramsen Tropical Forests for the first time.  

The gorillas soon made their way towards the habitat, and Koola, the 30-year-old mother of three, was the first to officially step foot in the outdoor portions of the habitat complex. She was quickly followed by the other five females, each taking their time to explore the multiple levels and different substrates of the habitat. Jontu, much like a wild silverback male protects his family group, kept a watchful eye on the females from a chute above while they took their first steps into the habitat. He was the last to enter the habitat.   

Month One: Spotting Positive Welfare Indicators

While the gorillas appeared to readily adopt their new habitat on day one, our study continued through the summer to help us determine how the gorillas’ welfare status may change over time in Bramsen Tropical Forests.  

We conducted observation sessions twice per day for the first month in their new habitat, recording the gorillas’ behavior, social interactions, and where they chose to spend their time in the habitat. We noted data on tablets at one-minute intervals, watching one gorilla for 10 minutes before moving to another. The following specific behaviors, or welfare indicators, were selected because of their relevance to gorilla natural history, or how they would typically behave in their natural range.  

Gorillas are social animals, with one of the most characteristic social structures being a family group of one silverback male, multiple adult females, and their offspring. As such, behaviors like grooming each other and spending time in close physical proximity are important to maintaining a strong family unit and are often used as indicators of positive gorilla welfare. Another important behavior for gorillas is feeding, due to the copious amounts of plant matter they are required to consume to maintain a healthy weight and body condition. Finally, because gorillas are primates, they possess specialized adaptations for climbing and are often observed scaling trees in the wild, so time spent above ground is regularly used as another indicator of positive welfare.  

While our study is still ongoing, the preliminary results show that the gorillas are regularly displaying natural behaviors in their new habitat. As a whole, the family group has spent about 15% of their time feeding, and they could regularly be observed feeding on various fruits and vegetables in close proximity to guests near the viewing glass.  



The data also suggested enduring social bonds in their first month, with the majority of the gorillas grooming other gorillas in the group, also called allogrooming, and spending roughly 15% of their time in close physical proximity to at least one other gorilla. In month one, the “social butterfly” award was jointly handed to the group’s youngest gorillas, Nora and Ali. Nora spent nearly one quarter of her time within an arm’s length of another gorilla, while Ali spent the most time allogrooming of any of the gorillas.  

Most excitingly, the gorillas appeared to take advantage of the new heights of Bramsen Tropical Forests, spending 30% of their time above the ground, and 15% of their time over 20 feet above the habitat’s floor!  
 

Year One: Using Technology to Study Primate Welfare

Data collection will occur again this upcoming fall and winter to assess how the gorillas are adapting to the habitat over time, as well as to the changing seasons. While the early behavior trends we observed were promising, it’s important to regularly collect data because animal welfare is not static and can change over time. Collecting data and assessing the gorillas’ welfare regularly allows us to make the best-informed decisions to continually optimize the gorillas’ health and wellbeing in Bramsen Tropical Forests.  

However, to continue Brookfield Zoo Chicago’s status as a leader in animal health and welfare, we are also implementing innovative new methods to better understand habitat spaces and how animals perceive their worlds. Large-scale habitats like Bramsen Tropical Forests often present difficulties when trying to quantify available space, especially the behaviorally relevant climbing structures.  

To better understand how arboreal species like primates use their habitat, I was inspired to find ways to measure and study not just the ground areas, but the full space. Using camera-outfitted drones and a photo analysis process called 3D photogrammetry, we will be constructing hyper-realistic 3D digital models of Bramsen Tropical Forests. From these models, we will be able to quantify the space available to the gorillas to a degree of accuracy not previously possible through traditional physical measurement. I designed this study method alongside partners at Cleveland Metroparks Zoo, and now Bramsen Tropical Forests will also be the largest habitat modeled using this technology!  

Additionally, these drone-based images of the habitat will allow us a unique look at the space from the gorillas’ perspective, especially from the upper reaches of the habitat. We will be conducting different analyses of these images to determine how the complexity of the habitat affects where the gorillas choose to spend their time.  

As we continue to collect data and conduct analyses, we are looking forward to sharing the sharing the results of our study of Brookfield Zoo Chicago’s largest and most innovative habitat project to date!