What a Lizard Wants

When you walk into the Holden Reptile Conservation Center, directly on your left is a lush habitat full of vibrant plants and the sound of a trickling waterfall. As you walk to the other side of the habitat, you may see a roughly six-foot-long lizard floating in the pool, or he may be stretched out, soaking up the rays from a heat lamp. This is Solair.

Solair is an 11.5-year-old water monitor (Varanus salvator). He arrived at the Detroit Zoo in early 2015 after his previous facility could no longer care for him. Although Solair may be considered a senior for his species, you would never know it! He is a charismatic individual who enjoys interacting with his care staff and exploring his habitat to find the tasty fish they leave for him.

Figure 1: Solair, an 11.5-year-old water monitor, resting in the pool of his new habitat, completed in April 2021.

Solair’s current habitat was completed in April 2021 with the generous support of individual donors and a grant by the Michigan Council for Arts and Cultural Affairs. The habitat is more than 900 square feet, which is almost five times its original size! A major feature is the 7,000-gallon pool with a waterfall. His basking lamp shines in a cave with a heated floor, and two other heated rocks can be adjusted to keep him comfortable throughout the year. Natural light shines through the front windows and skylights, allowing live plants to thrive and creating a tranquil atmosphere. The only piece of the habitat that remains the same from before the renovation is Solair’s favorite log that he likes to climb and where he occasionally sleeps.

Figure 2: Solair is looking out from one of the logs surrounded by plants and natural sunlight.

Major habitat modifications like this come with many considerations. How do we know that Solair likes the changes we made? How do these changes affect his welfare? The Association of Zoos and Aquariums defines animal welfare as an animal’s collective physical, mental and emotional states over a period of time, and it is measured on a continuum from good to poor. To monitor how habitat modifications affect an individuals’ welfare, we perform a post-occupancy evaluation. This evaluation looks at how an animal used their previous space compared to their new habitat.

For a post-occupancy evaluation, we may look at a variety of animal welfare indicators, such as investigation and species-appropriate behaviors. When animals spend time investigating their habitats above the amount required to find food and shelter, it is interpreted as enjoyable and self-rewarding. Due to the energy needed and risks that could arise from investigating in the wild, this behavior can also signify that an animal feels comfortable in their habitat. From his first introduction to his new habitat, Solair appeared very comfortable. He almost doubled his time investigating compared to his previous habitat as he checked out every nook and cranny of his new home. As a water monitor, this included particular attention to exploring every inch of his spacious pool.

Species-appropriate behaviors, like water-based behaviors for water monitors, are considered during all habitat modifications. We want to provide spaces that allow animals to behave as similarly to their wild counterparts as possible. Water monitors have a fascinating repertoire of behaviors seen in the wild. They are usually found by the water and can swim long distances if needed. Water monitors create burrows in the banks of rivers, carving out a chamber with shallow water where they sleep. They have powerful legs that help them chase down prey across land or in the water. Solair’s new habitat has given him the space to spend more time digging, swimming and floating. Solair also has spent more time on land moving between different habitat features, which helps him build muscle and maintain a healthy weight.

Changes in specific behaviors provide hints about overall welfare, but we also try to look at more comprehensive welfare indicators, including behavioral diversity and the spread of participation index (SPI). Behavioral diversity measures the number and frequency of behaviors displayed by an animal. In general, higher behavioral diversity is considered a positive welfare indicator, suggesting an animal has the resources and comfort to perform a variety of behaviors. When Solair was introduced to his new habitat, his behavioral diversity increased partly due to the new behaviors the habitat allowed him to perform.

The SPI has been gaining interest as a welfare indicator, and it assesses how evenly an individual uses the space provided, providing information on how different areas of the habitat meet individual needs. Typical SPI values vary from species to species. For example, grizzly bears generally move more than most snakes. However, suppose an individual never moves from one spot. In that case, the habitat may not provide the resources that the individual needs or the comfort to use the resources provided. Solair uses his current habitat more evenly than his previous one. However, he still has favorite locations, as seen in the heat map of his location use. The pool and his heated cave are two of the places where he spends the most time.

Figure 3: A heat map of Solair’s space use. This map shows the Holden Reptile Conservation center entrance on the right side and the exit on the left side. Areas in blue and green are less used, whereas areas in yellow and red are highly favored.

Solair’s new habitat has many positive features for him and Zoo guests, including ample options for people watching. Frequent visitors know that Solair occasionally will engage with small children and will often watch guests throughout the day. There were also many neutral and mildly positive relationships between the amount of time a crowd was in front of Solair’s habitat and his use of space and behavioral diversity. However, we have noticed one drawback: with the increased glass in the new habitat, guests are tapping on the glass more frequently. Unfortunately, there were decreases in Solair’s welfare indicators on days when guests engaged in more glass tapping. Part of the scientific process is to notice trends in the data and begin asking new questions, revealing new study ideas. The Detroit Zoological Society will continue to do this with the aim of providing the animals we care for with the best lives possible. However, we also ask our guests and wildlife lovers everywhere to remember that you play a part in the welfare of animals at the Zoo, other organizations and in the wild.

Overall, Solair has adjusted well to his new habitat and seems to enjoy all of the new features provided. We hope next time you visit the Zoo, you will make sure to stop by and say hi to Solair in his new habitat. Just remember he prefers a friendly wave over a tap on the glass.

Jennifer Hamilton is animal welfare programs coordinator for the Detroit Zoological Society