Sunlight, or the lack thereof, is closely linked to many different aspects of animal behaviors, and with it, many unique adaptations. Some animals are active during the day, basking in the sun’s rays to regulate their body’s temperature. Many crepuscular species (animals most active at twilight) take advantage of the dimly lit dawn and dusk to conceal themselves from their prey while hunting. Finally, nocturnal species may use alternative navigational behaviors, like echolocation, to successfully traverse their habitats without sunlight. Lighting conditions are not only important to daily activities, like basking and foraging, but are integral to behaviors that occur at much larger scales and over longer durations. One example is the monarch butterfly, a species that uses the sun’s position as a natural compass during their 3,000 mile long migration.

Given light’s importance to behaviors ranging in scale from daily foraging to continent spanning migration, lighting conditions are an aspect of animal care that are closely monitored in order to positively affect animal welfare. You may see different lighting systems and strategies around Brookfield Zoo Chicago, ranging from specialized basking light bulbs in the Reptiles & Birds building to the faint, dusk-like lights in the Rodrigues fruit bat habitat in the Australia building. Zoo and aquarium scientists have published a range of studies investigating the impacts of different lighting systems and strategies on animal welfare. One example is a study that examined the effects of two different light colors (red and blue) on the behavior of nocturnal primates housed in zoos. Nocturnal animals are often housed in habitats using these primary colors because these animals typically have a limited ability to see these colors’ wavelengths. Thus, these lights have minimal impact on the animals’ typical activity and sleep cycles, while allowing zoo guests and staff to easily observe these unique species. This study found that not only were animals less active under blue light, but displayed lower concentrations of the hormone melatonin, which is responsible for maintaining the body’s proper circadian rhythm. These results suggested that using red lighting systems for nocturnal animals may be the best strategy for optimizing welfare (¹⁾.

Brookfield Zoo Chicago’s animal welfare science team is currently engaging in research examining the effects of different lighting conditions on two different groups of animals – two pinniped species (California sea lion and northern grey seal) and three shark species (leopard shark, horn shark, and swell shark). Pinniped eyes are specially adapted for the often low light conditions underwater, where the sun’s rays can have difficulty penetrating. Depending on the weather conditions, our pinnipeds can experience a range of different lighting conditions, from muted to intensely bright. We are currently observing our pinnipeds over the course of one year to determine whether their behavior or space use is affected by changes in the environment related to light, temperature, UV index, and surface reflectivity. The results from this work can help us determine how to best design their habitats to promote optimal health and welfare. Aquarium-housed sharks, on the other hand, do not often experience natural lighting conditions, as their aquarium habitats are fully indoors. To support the health and welfare of our sharks, Brookfield Zoo Chicago has implemented an innovative lighting system that can mimic the natural variation of sunlight during the day, as well as moon cycles at night. Very little research has been done on the effects of natural lighting systems on the welfare of aquarium-housed sharks, so stay tuned as we find out more later this year!

Charles Ritzler, PhD
Animal Welfare Scientist
Published March 4, 2025
 
^{1: Fuller, G., Raghanti, M. A., Dennis, P. M., Kuhar, C. W., Willis, M. A., Schook, M. W., & Lukas, K. E. (2016). A comparison of nocturnal primate behavior in exhibits illuminated with red and blue light. Applied Animal Behaviour Science, 184, 126-134.}