Oaks and acorns have fostered an unlikely association between a predator and its prey. Primatologists notice that Himalayan black bears could be actively seeking out langurs during the oak fruiting season: not to hunt them, but to feed on the acorns that the primates accidentally let fall to the ground.
There are several instances – from India and other countries – where unrelated species benefit from feeding in the same area that others feed in. Herbivores such as deer often feed on forest fruits and remnants that fall when primates pluck out and eat fruits from trees above. It was while studying patterns of how central Himalayan langurs feed in Uttarakhand's Kedarnath Wildlife Sanctuary that researcher Himani Nautiyal (of Kyoto University's Primate Research Institute) suddenly noticed that in specific months, Himalayan black bears were frequenting the same area as the langurs. The bears, which are known to eat langurs when their usual food resources are scarce, would position themselves under the fruiting oaks on which langurs were perched and feast on the acorns (oak fruits) that fell.
Intrigued, Nautiyal and her colleague studied this in detail. Between June and September 2016, they spent 468 hours studying the behaviour of a troop of 26 langurs and looking for signs of bears nearby. Their results, published in the Mammal Study, show that the percentage of individual langurs feeding on acorns was highest in the months of July and August — the same months that acorn season peaked. Nautiyal’s three direct sightings of bears feeding on fallen acorns was also during these months.
“The bears were never far from the langurs during these months,” said Nautiyal. “Sometimes they would even sleep under the trees that langurs slept on.”
The team also frequently observed pale bear scat (caused by digested acorns) under these oaks; other indirect bear signs in the area included mangled shrubs (as bears searched for fallen fruits) and even bear sleeping dens dug out of tree hollows. So could it be that bears are deliberately tracking langurs during this season to feed on fallen acorns?
“Yes, we think it could be an adaptive strategy by the bears,” said Nautiyal. “It increases their foraging efficiency. They would not have to spend time climbing oaks to access these fruits, especially females with cubs.”
However, longer-term studies would be crucial to understand this unique and never-before-reported feeding association between langurs and bears, she added.