How our bears prepare for torpor through seasonal diet changes

As our four European brown bears, Neo, Nilas, Albie and Gemini, prepare for their months of torpor we wanted to share their seasonal diet changes that enable them to be ready for this state of winter inactivity.

(Photo credit: Jon Drew)

European brown bears are opportunistic omnivores and eat anything from tree bark, leaves, nuts, fruit, and vegetables, to meat, including small rodents, birds, and fish. It is safe to say that they are not fussy eaters, however, what they eat differs throughout their active seasons.

Here at Bristol Zoo Project, our Animal team change up the bears’ diet seasonally to mimic what would happen in the wild.

When they emerge from torpor in early spring, usually between February and March, their appetites aren’t fully ready to take on too much food as they continue to be in a state of ‘walking hibernation,’ where they sleep a lot more than other months. During this time, they tend to pick at grass, lettuce, and other leafy vegetables, as well as maintenance pellets and a small amount of meat, as well as gently foraging for ants and plant material within their habitat in Bear Wood.

From mid spring the bears become more food-orientated, which is called the hypophagia stage. During this time the bears need more protein after torpor, and we ensure to provide a large amount of meat in their diet.

Late spring through to summer they begin to think about gaining enough body mass for the winter. In this season they are keen to munch away on starchy and watery vegetables, including sweet potatoes, peppers, and celery, as well as their food pellets. Mealworms are also added into their diets at this time of year as in the wild this is when bears will be consuming large amounts of insects.

By late summer and into early autumn their appetite has ramped up dramatically, a state known as hyperphagia, and the keepers begin to up the quantity of food available and switch up the offering to a much fattier diet. They shift to a higher percentage of fruit and nuts along with the other bits of vegetables, protein, and pellets from the previous seasons. It is during late summer and into autumn that keepers introduce fish into their diet, again mimicking what the bears would eat in the wild. This time of year, our bears also go mad for peanut butter, which is used as part of enrichment exercises by our team, as they smear peanut butter on different trees and trunks, as well as in nooks and crannies of their habitat so their noses have to lead the way.

Towards the end of autumn, food is all our bears can think about, and their diet now includes a large amount of fat and natural sugars on top of the vegetables and insects. They choose what they need to maximise their weight gain and are offered as much variety as possible.

(Photo credit: Doug Lodge)

Their habitat in Bear Wood is perfect for foraging some of their favourite things, such as blackberries, elderberries, acorns, hazelnuts, and the browse that grow naturally. Keepers continue to use food as enrichment and by this time of year, honey is the sweet treat they all crave. Much like peanut butter, honey is smeared around their habitat and their noses take them straight there for that all-important sugar hit. It is during this time of year you may see the bears waiting, rather impatiently, for the scattering of food just outside their den, looking longingly at the keepers and urging them to hurry up with their cleaning tasks. They will also rush to gobble up all the good bits first, including fruits and nuts, but they all very much have their own preferences. For example, Albie loves strong herbs, such as coriander and parsley.

The seasonal shifts in the bears’ diets and their food drive has quite a big impact on their behaviour. In springtime they are seen to be more playful, testing each other’s boundaries through play fighting whilst in the autumn their relationships change as they are in more competition for food and have a focus on eating as much as they can. However, as soon as they begin to enter torpor, they snuggle up in their family pairs for the majority of winter, which you can see on camera on our Bear Wood torpor screen.

Weight gain between the bears differs slightly and male Neo often comes in with the highest weight coming out of torpor last year at 302.5 kg, having gone into torpor at 360kg. Female Gemini comes out of torpor at an average of 168.5 kg and usually enters it 40kg heavier. A lot of the fat they build up is in the form of brown adipose tissue, also known as BAT or brown fat. This fat builds up in different locations on hibernating animals, but in bears, it tends to be stored in patches near the brain, heart, and lungs. This fatty tissue has more mitochondria than white fat and is therefore richer in iron. These patches of brown fat are specialised in generating heat, in a process called adaptive thermogenesis, and maintain the core body temperature despite reduced metabolic activity over the cold months.

For more information about torpor head to our blog here.

(Photo credit: Katie Horrocks)

Bear Wood at Bristol Zoo Project

Bears, alongside the other inhabitants of Bear Wood – wolves, lynxes and wolverines – used to roam Ancient Britain 10,000 years ago. Due to hunting and habitat loss, they’re now extinct in the British Isles. Every visit to Bristol Zoo Project helps to support our conservation efforts and prevent species extinction.

Make sure to book your visit soon to see the bears before they go into torpor! Over winter you’ll be able to watch them snoozing in their house on our Bear Cam, which is on the main walkway in Bear Wood.