The Detroit Zoological Society (DZS) is investigating the effect of foraging opportunities on the welfare of the seals who live at the Detroit Zoo. Foraging is a very important behavior category for animals, as it typically involves mentally and physically stimulating behaviors. Wild gray seals may spend up to two-thirds of their time searching for food. Although they do have well-developed hearing and sight, seals often rely on their extremely sensitive whiskers to locate the fish they eat. This is necessary as visual conditions underwater can be poor and swimming fish may not generate much noise as they move. Instead, the fish – and other prey items – create vibration trails in the water and these are the stimuli the seals’ whiskers detect. Research has shown that harbor seals can use their whiskers to distinguish between objects of different sizes and shapes – a skill they can use to select better prey items when hunting.
Seals living in zoos and aquariums don’t need to forage in quite the same way as they would in the wild, and thus may not engage in as many complex feeding behaviors. As part of her residency with the Center for Zoo and Aquarium Animal Welfare and Ethics, Sara Zalewski worked with DZS staff to design a project examining the impact of three different ways to increase foraging behavior in the gray and harbor seals living at the Detroit Zoo. The seals were presented with fish frozen in ice, fish placed on top of a floating disk and sunken tubes the seals needed to manipulate to allow fish to fall out of holes in the tube. All three items were used to increase the amount of the work the seals would have to do to get to the food. As part of this research, Sara found that the seals differed by both species and individual in how they used the items.
The gray seals interacted with the items most when they were first presented with them, and the harbor seals’ level of interaction increased as time went on. The likely explanation for this is that the gray seals were younger and more dominant, and thus were able to use the items more easily. Once they had their fill of the food, they would lose interest and the harbor seals could begin to investigate the items. Dealing with dominance hierarchies can create challenges when providing animals with resources, and is therefore something we have to keep in mind when thinking about the welfare of all of the individuals.
Another challenge was getting the seals to use the items for longer periods of time. It makes sense that less interaction occurs without the motivation of obtaining food, so there is a need for more challenging devices that require the seals to use more of their foraging abilities. One unexpected outcome was that Georgie, one of the female gray seals, would sometimes use a floating disk as a resting place later in the day. However, it could not support her body weight, so she would lay on it on top of something else, such as a ledge in the pool. Other studies have shown that gray seals’ preferred prey, haul out sites, and feeding locations and techniques differ greatly between individuals. Finding ways that items can serve more than one purpose and allow each seal to make use of them as they choose are also goals.
Harbor seals are an especially playful species, including as adults. However, as animals age, play and exploratory behavior tend to decrease, regardless of the species. Additionally, decreases in their sensory abilities may occur. This means that for Sydney, the older male harbor seal, opportunities may be more challenging or potentially less engaging for him.
In order to create more engaging ways for all the seals to forage, Sara worked with DZS staff to refine the items and will observe Georgie and Jersey, the two gray seals, and Sydney, the harbor seal, to see how the modifications affect their behavior. DZS staff members are creating floating devices that the seals can use to rest – as well as interact with for access to fish – and are changing the design of the tubes so that they rest standing up, rather than lying flat on the bottom of the pool. This should make it a bit harder for the fish to fall out, and will be more stimulating for the seals as a result. Finally, Sydney will have some alone time with the items, to ensure the younger and more agile females don’t deplete the food before he has a chance to interact with the foraging devices. During your next visit, you may see these items in the seal pool at Arctic Ring of Life. Although we are only observing the seals at specific times, incorporating these types of behavioral opportunities is part of our daily comprehensive program of ensuring the environments for all the animals at the Detroit Zoo are ever changing and appropriately complex.
– Dr. Stephanie Allard is the director of animal welfare for the Detroit Zoological Society and oversees the Center for Zoo and Aquarium Animal Welfare and Ethics.