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Here at the zoo, most of our leaf-eating mammals come from tropical climates where they can browse on leaves all year long, but in Jersey, most trees lose their leaves over winter. So, we created a new winter “browse” plan to improve the welfare of these animals at the zoo. “Browse” is the word used to describe edible vegetation, such as branches, shoots and leaves.

Historically, like most other UK zoos, we have used bamboo and hay to supplement the diet of browsing mammals during the colder months. Compared to the summer, when primates are offered a wider range of browse, we worked with a reduced variety of leaf feeds in the winter. This also decreased the animals’ social interactions, as primates spend time together as they de-leaf stems and feed on browse. 

This year, we have created our own leaf silage, which stores browse over winter by fermenting leaves in barrels for up to 20+ weeks. Leaf silage is often prepared for ungulates in zoos, but is not widely used amongst primates, so this has been an exciting trial period for us and the wider zoo community.  

Overall, we have used 10 plant species, including lime, hazel, sweet chestnut and sycamore, all of which are local plants grown right here in the zoo over the summer. The animals are fed these plants every day in the warm season. We cut the leaves back from these and fill 30-litre barrels, pushing down on the pile to squeeze out all the air. By the time you put the lid on, it should be a struggle to make it fit! All you do then is leave the barrel in a cool, dry place to ferment. If you don’t open the barrel, it should break down into silage. It’s just a matter of patience.

A colleague and I attended a BIAZA (British and Irish Association of Zoos and Aquariums) silage and browse conference at Chester Zoo last year, where we picked up great tips on managing their silage for the rhino, elephants and giraffes. The conference was mainly focused on these large ungulates, but we knew we could adjust it for our zoo. So far at Jersey Zoo, we have fed it to the gorillas, orangutans, gibbons, bats, giant jumping rats, lemurs, geladas, sloths, howler monkeys and pigs! It’s been a real hit across the board, with each species preferring different leaves. The gorillas in particular have hoovered it up. Badongo, our silverback western lowland gorilla, is so eager for it he will push his daughter Amari aside to get more than his fair share! She will sit and watch dad waiting for any scraps he may drop.

Another new winter browse initiative, inspired by Chester Zoo keepers, is growing our own willow whips inside to produce fresh leaves. We have been cutting 50 willow sticks each week, putting them in a warm and dark place in water to grow roots, then moving them into the light. Within four to five weeks, we have fresh leaves! Something the apes have never been able to have over winter in Jersey. The gorillas will eat all leaves, bark and even the roots from this indoor grown plant. 

This project has had a massive benefit to the welfare of the animals during the winter months. We are collecting data from all we do to scale up and increase production for an even better 2025/26 winter!