Jays and acorns

A few weeks ago, on a local urban walk, I had the chance of watching some Jays collecting acorns from the oaks. It's been a good mast year and the veteran oaks at the cemetery were laden with acorns. Jays are a scarce and shy species in my city, but occasionally I come across them in the most wooded green spaces. These individuals, at least two, were collecting acorns, flying back and forth from the tree to their larder, a site out of sight beyond the road. Before disappearing into the foliage of the still green oak, they often paused on trees nearby, which is how I took the photo below, the wind pushing the Jay's crest up.

Caching behaviour

Jays are omnivorous and opportunistic in their food habits, but during autumn they become dedicated food hoarders. They are resident birds that depend on their stored harvest to survive the winter and early spring, and are acorn specialists. They have a pouch under their tongues and can carry up to nine acorns in a single trip, although in 80% of trips they will carry one or two. Their acorn reserves will be scattered, a single acorn buried in a shallow hole in the ground, around their home range, and the reserves will be steadily used. You might see Jays in small parties - often detected by their screeching calls -  but they tend to be mindful before they bury each acorn, away from the prying eyes and ears from other Jays, which will be all too happy to pilfer other individual's hoards. Experiments by Nicola Clayton's group have shown that their caching behaviour is dependent of potential pilferers being around and they will cache preferentially behind an opaque screen when other individual is watching, if they are within earshot of other individual, they will cache in quieter substrates (sand) rather than noisy gravel.

Oak foresters

Jays can store several thousand acorns per year, and rely on their spatial memory skills to retrieve them.  They have a mutualistic relationship with oaks, being crucial dispersers of acorns. As not all acorns will be consumed by jays, oak long-distance dispersal depends mainly on Jays, and the forgotten or unused acorns are perfectly planted to successfully germinate. The dispersal distance,estimated using radiotransmitters inserted in acorns provided to Jays in feeders in the landscape ranged from a few meters up to about half a km.

A Jay with an acorn it has just retrieved. It took about minute to find it. Watch the full clip here:

Complex cognitive abilities

It is striking that Jays manage to remember the location of thousands of caches. As other caching birds, they have excellent spatial memory, and perform very well in spatial memory tasks. Experiments have also shown they have episodic memory, an ability to recall specific events and details, both when caching and when pilfering. They might also prefer to cache near vertical structures, which might facilitate recall.

Jay with peanut. Jays are part of the bird community of towns and cities, particularly when tree cover and food resources (oaks or bird feeders) are available. 

More information

Kurek, P., Dobrowolska, D. and Wiatrowska, B., 2019. Dispersal distance and burial mode of acorns in Eurasian Jays Garrulus glandarius in European temperate forests. Acta Ornithologica, 53(2), pp.155-162.

Legg, E. W. & Clayton, N. S. Eurasian jays (Garrulus glandarius) conceal caches from onlookers. Anim. Cogn. 17, 1223–1226 (2014).

Madge, S. and G. M. Kirwan (2024). Eurasian Jay (Garrulus glandarius), version 3.0. In Birds of the World (B. K. Keeney, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.eurjay1.03

Pons, J. & Pausas, J. G. Acorn dispersal estimated by radio-tracking. Oecologia 153, 903–911 (2007).

Shaw, R. C. & Clayton, N. S. Careful cachers and prying pilferers: Eurasian jays (Garrulus glandarius) limit auditory information available to competitors. Proc. Biol. Sci. 280, 20122238 (2013).   

Rooks hoarding acorns

It is a mast year, with a bumper crop of acorns across the city. October is peak acorn season and last week I saw the first Rooks carrying acorns. Acorns are packed with energy, and several bird species take advantage of them. Woodpigeons, presumably swallow them whole from the trees, but Rooks and Jays collect the harvest and store it for use during the winter. Both species are scatter hoarders, and cache individual acorns on the ground, and use their extraordinary spatial memory to recover them later in the year, when other food resources are scarce. Although the Jays are best known for this behaviour, Rooks are also amazing acorn hoarders. Rooks can transport acorns - and other food items - in a pouch under their tongue, which obviously bulges as they fly over with their pouch full. The number of acorns they can carry depends on the acorn size, and varies from 2 to 7. They prefer to cache the acorns on grass, and can fly up to 4 km from oaks to suitable grassland. Once they find a good spot, they drop all the acorns they are carrying and bury each one by one, by first making a hole in the ground with their bills, and then hammering the acorn in and covering it with grass, leaves or soil. Later on, they will visit the caching sites in the winter, find their stored acorns and crack them open to feed. 

A vocal Rook on an oak canopy, surrounded by plenty of acorns.

Rooks, unlike Jays, are very social and engage in communal acorn collecting, becoming very vocal when landing on the oaks canopy. They prefer to gather acorns with other Rooks, and individuals appear to join other individuals gathering acorns by flying in the opposite direction of individuals with full bills. When it comes to caching though, Rooks prefer to be alone, to avoid cleptoparasism, when other individuals try and steal their stored acorns.

Rooks displaying, the individual on the right, with distended sublingual pouch, passed an acorn to one on the left, presumably they are a mated pair.

More information

Waite, D. R. K. Food caching and recovery by farmland corvids. Bird Study 32, 45–49 (1985)

Källander, H., 2007. Food hoarding and use of stored food by rooks Corvus frugilegus. Bird Study, 54(2), pp.192-198.

Gobbling up acorns

In the last few weeks it has become apparent that this is an acorns mast year, a bumper year for these seeds - and also for many berries. The evergreen oaks in my local park have not been an exception: Grey Squirrels and Woodpigeons are enjoying this bonanza and feeding on fallen acorns on the ground and the remaining ones in the tree. Today a large flock of Woodpigeons, including many juveniles, feasted on acorns in the park. I managed to record some videos of the feeding activities of the Woodpigeons in the trees and the ground underneath. I find it amazing that the Woodpigeons swallow the acorns whole, presumably their digestive system dissolving the tough shells.
At some point in the sequence, something scared the woodpigeons and most of the flock took to the air. The one I was filming stayed put in the tree, looking up nervously.