Have you noticed what an extraordinary year it is for acorns? Almost without exception oak trees everywhere are laden. It’s a phenomenon and it’s got a name. It’s a Mast Year.
A Mast Year occurs roughly once every 5-10 years and is when oak trees – though it can be other species – drastically increase the number of acorns they produce. The name derives from the Old English word ‘mæst’, meaning the nuts of forest trees that have accumulated on the ground, especially those used for fattening pigs.
The only downside is that they put so much energy into this bumper performance that they leave themselves little energy to continue producing the following years. That seems rather strange so why do they do it?
Mast Years are a canny strategy to increase the survival of future generations. By producing so many at the same time it’s impossible for them all to be eaten by anyone looking for an acorn dinner, which means many more survive to sprout into the next generation. Clever! But here’s the thing, it’s got to be a group thing – no point the odd tree here and there deciding to do its own thing and go ‘Mast’, no, it only works if all the other trees in the wood do it at the same time. Like foxgloves that flower in the spring but only every other year and they all do it in sync. How do they all know if it’s an on year or an off year, who tells them?

A Mast Year is of course a huge bonus for all the wildlife that rely on nuts for their winter food. We have a squirrel that runs along the post and rail fence in front of our bedroom window collecting bounty from our walnut tree.

But by far the biggest collectors and stashers of acorns, in a league of their own, are jays. Their Latin name is Garrulus glandarius, meaning ‘chatty’ and ‘acorn’, which is an indication of just how close a relationship this bird has with oak trees and their acorns.

Although it’s the only walnut tree on the farm someone must have done a ring round as it seems to have got wind of the 2025 Mast thing and is also laden.

Each morning we see him scurrying along the rail on his way to collect yet another nut – a tad annoying as I always plan to fill the pantry with pickled walnuts, although it is very endearing to see him on the return journey looking important with a nut tucked into his armpit on a mission to bury it somewhere in the garden. But by far the biggest collectors and stashers of acorns, in a league of their own, are jays. Their Latin name is Garrulus glandarius, meaning ‘chatty’ and ‘acorn’, which is an indication of just how close a relationship this bird has with oak trees and their acorns.
In a typical year jays collect up to 5,000 acorns, actively selecting the largest most viable ones to bury in open scrubland where shade-intolerant oak trees can then establish themselves and thrive. And by using vertical structures, usually trees, a jay can recall where it buried about 75% of its cache, leaving around 25% to germinate. But it doesn’t stop there.
A jay’s seasonal foraging behaviour further helps the oak in that it rarely hunts for its stash during the sensitive early spring germination phase and is much busier during May to July once it has offspring to feed. And if it comes across an oak seedling growing in a spot where it recalls burying an acorn, it will uproot the young plant, eat the acorn, and then crudely replant it – and the seedling usually survives. Now isn’t that extraordinary!