A Guide to: The Oak & The Jay (a symbiosis)

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Jays are colourful members of the Corvid family, related to Crows and Ravens. They inhabit most of mainland UK year round, in woodlands and forests in both rural and urban areas. Jays store food with technique known as ‘caching’ - this means they find food which they then bury in a safe place, to return to and unearth during times of food scarcity. Their favourite food for caching is the humble acorn.

Plants have many different ways of dispersing their seeds when the time comes. Sycamores have ‘helicopter’ shaped seeds which float in a spiralling motion away from the tree on the wind. Dandelions utilise the wind to take their fluffy blow-ball seeds further away. In the summer heat, gorse bush seed pods burst open with such force that seeds will go flying up to 5 meters away. The bramble encourages birds and mammals to eat its delicious blackberry fruits, which then get dropped off at other locations later - with extra fertiliser! Like many other trees, oaks let their seeds - the acorns - fall from the tree, landing directly underneath the branches. This is where they stay and they rely on animals to take their seeds elsewhere. Like jays, squirrels also love acorns and will cache them in a similar way to jays, burying them in stores which they hope to remember the locations of in the coming months.

A mature oak, between 40 and 120 years old, can produce 10,000 acorns in a mast year (a year when there is a bumper crop). An oak will not start to produce acorns until it is around 50 years old and, over the span of its lifetime, will produce around ten million of them. Jays will return to their buried acorns year round, but less so between the months of April and August, and it is during this undisturbed period that the acorns start to germinate. When the seedling starts to show its first few leaves in June, the jays will be busy feeding their young, and they start to search for their buried acorns with more intent around this time. If they find their buried seed, now a sapling, they will dig it up and eat the acorn. You’d think this might damage the sapling, but in fact the oak has evolved to be able to withstand this attack from the jay, and allow it to feed whilst remaining strong enough in the ground to keep growing.

Like their Corvid cousins, Jays are incredibly intelligent and have very good memories. This can come in handy considering a single jay can cache up to 5000 acorns in one season. Not all of these acorns will be retrieved of course - those which are lefts in the ground will, with any luck, grow into oak trees and begin the whole process again.

This whole process has been deeply ingrained into both the bird and the tree’s evolution, and experts now say that jays could be responsible for planting whole woodlands over the course of their and their descendant’s lifetimes.

Written by Jane Mutiny

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