Gorilla Rainforest
The day finally arrived to allow the gorillas access to their new habitat. This was planned a little ahead of the official opening – just to make sure they actually went out and explored. This was fortunate, as they showed very careful attention to moving past their door at first. Most interesting was the fact that the girls went out first. The big silverback male sat in the doorway, calling the girls back whenever they found any regular food (hidden earlier by the animal team) and gratefully taking it off them. A little bit like the good wife nipping up to the shops for the husband watching tv... Watching the gorillas pushing into the vegetation was an education in itself – for the gorillas and any observers. Remember, the gorillas had been used to a simple rough grass area plus a few turf weeds, and now they had this vast array of new plants. Will it hurt if they pushed through the plants? Are the plants edible? For the first few days, the gorillas even avoided cardoon Cynara cardunculus, jumping over it if it was in their path. On the very first day, one female gorilla targeted the purple willow Salix purpurea. Not surprising as they would have been given several different species of cut willow as browse for many years. But not S. purpurea. She pulled the plant up first. It was from cuttings we had raised in the nursery and nurtured. Groans came from the horticulture team. Laughs came from the animal team. She stripped the leaves off and pushed them into her mouth, instantly spitting them back out and throwing the plant stem down in disgust. Cheers from the horticulture team. Moans from the animal team. Then came the tentative question, ‘Is it poisonous?’
The gorilla seemed to be waiting for the willow catkins to get big enough, while his mangabey neighbours attacked the Gunnera manicata buds, taking just the flowers. Who taught who?
Purple willow Salix purpurea was immediately targeted as it was recognised as willow, which is normally edible. S. purpurea was selected for planting as it is not eaten by rabbits, due to the higher salicylic acid content making it very bitter. The salicylic acid in willow is a well-known plant source of aspirin. Years ago, the doctrine of signatures used for medicinal guidance said that trembling willow leaves were good for a trembling fever, and they were. No doubt, each gorilla and mangabey had to discover that this species is not nice to eat, and some plants were lost. But out of the 100 or so planted, enough have grown to 3m bushes to give a good shrubby look to some areas. After a few years, once large enough, S. purpurea started flowering, giving masses of catkins along the thin twigs, typical of a willow. Both the gorillas and the mangabey were seen one spring in the middle of the bushes, pulling the shoots down, stripping off growth, and letting go. Only with binoculars could anyone see what they were doing. Very carefully, the catkins – only the catkins, were being removed, no young leaves or bark and immediately popped into waiting mouths. Individual technique varied, maybe one catkin at a time, maybe a few. The gorillas were even seen with green chins from the pollen. Obviously proving a tasty and totally unexpected mouthful. The question remains, why? Is the catkin a temporary growth that the willow does not bother forming the bitter salicylic acid within? Is the nectar sweet enough to hide the bitter flavour? Most likely to keep the nectar sweet for pollinators, the bitter salicylic acid is not produced in the catkin. Once flowering stops, the willow is left alone again, until next year, apart from incidental damage from playing and climbing.
Slow foraging was great enrichment
One challenge encountered watching this interaction was the reaction from one of the gorillas. Whenever some of the horticulture team came around with a camera and binoculars to see what was being eaten, the gorilla immediately stopped doing whatever it was engaged in, looked up, watched, and shadowed the photographer all around the moat, always looking directly at the photographer. But only when the photographer was wearing the zoo uniform or was alone. If they went around with a group of visitors, they were not noticed so easily. The best pictures were taken while taking guided tours around. Indeed, the observer does sometimes change the observed.