The Acorn and the Jay

An Eurasian Jay holding an Acorn in its beak about to bury it in the grass (photo taken through a glass window).

Earlier this month I had a wonderful encounter with an Eurasian Jay that was busy burying an acorn, which got me curious about the relationship between the two.

We've had Oak seedlings pop up in our garden before, which, in the notable absence of Grey Squirrels, almost certainly had to have been planted by Jays, but I had no idea of the importance or complexity of the relationship between the two species.

The Eurasian Jay has a fantastic Latin name of Garrulus glandarius, meaning "chatty" and "acorn" respectively, which is an indication just how close a relationship the bird has with Oaks and their acorns.

Jays collect and store large quantities of acorns of Quercus Oaks in a mutualistic relationship that disperses the keystone Oak species in open scrubland where the shade intolerant tree can establish itself well, even choosing the largest most viable acorns. An estimated 2,200- 5,700 acorns are "scatter hoarded" in this way during autumn.

The Jay, a highly intelligent member of the Corvid bird family, then utilises vertical structures nearby to remember the location of approximately 75% of its cache, leaving around 25% of the acorns to germinate. Jays are only able to find acorns they've cached themselves or observed another bird caching.

Jays are believed to prefer the most nutritious acorns, selecting large acorns of Quercus ilex, Quercus suber, and Quercus faginea, whilst avoiding acorns from Quercus coccifera. Quercus ilex acorns having the highest fat content while Quercus coccifera acorns contain the most tannin of the four species.

In my case the acorn was cached 77 yards / 70.4 metres away from the parent tree, which corresponded well with research I found on their scatter hoarding behaviour. In one two year study dispersal distance ranged from 3m to 456m from the parent tree, with most acorns cached less than 100m from the source Oak.

Jays seasonal foraging behaviour further helps the Oak in that they hunt acorns least during the acorn's sensitive early spring germination phase. Jays then resume acorn hunting more intensively during May to July once it has offspring to feed. When a Jay comes across an Oak seedling growing in a spot where they recall caching an acorn, they will uproot the young plant, eat the acorn, and then crudely replant it, which the seedling usually survives.

Thanks to the Jay's important role in the spread and renewal of keystone Quercus Oak tree species in the landscape they have become known as "ecosystem engineers". One Swedish study even attempted to calculate the replacement cost of the oak planting "ecological service" that Jays provide for a particular municipal parkland area.

Resources and References

This insightful Aboriculture Blog summarising a chapter from Vera, F. (2000) Grazing Ecology and Forest History

Animal Diversity - Eurasian Jay Species Account

Dispersal Distance and Burial Mode of Acorns in Eurasian Jays Garrulus glandarius in European Temperate Forests , P Kurek, D Dobrowolska, B Wiatrowska, Acta Ornithologica, March 2019

Observations on the collection and burial of acorns by jays in Hainault Forest, MR Chettleburgh, British birds 45, 359-364, 1952

Spatial patterns of dispersal, seed predation and germination during colonization of abandoned grassland by Quercus petraea and Corylus avellana, Johannes Kollmann, Hans-Peter Schill, Vegetatio 125, 193-205, 1996 

Acorn dispersal estimated by radio-tracking, Pons, Josep & Pausas, Oecologia153(4):903-11, 2007

A Kestrel Comes to Stay

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Falco tinnunculus, juvenile

Our next autumnal excitement arose from a series of long sightings of a young Kestrel, Falco tinnunculus, at the end of October. Whats the big deal? You might ask. After all, we see kestrels hovering in the paddocks and fields surrounding our home all the time. And have even enjoyed the odd fly by or spotted one perched up on our boundary telegraph pole looking out for prey.

But in eight years I’d never actually seen a Kestrel actually land on our property and I’d never ever observed one so close up before, especially not for so long at a time, and repeatedly over a period of several days.

We suspect he or she might be a juvenile ousted from the family home as they disperse widely in Autumn. Or else they could have been a young immigrant, newly arrived from Europe, as Kestrels living further north migrate southwards to overwinter where there is more food available.

We know its a young bird as juveniles have much more diffuse pale buff streaks on their undersides rather than the clear, dark distinctive spots on the plumage of adult birds. Young birds of prey are generally paler and and darken as they mature. The paler head could possibly mean its a male according to our detailed Collins “Birds of Prey” ID book by Benny Gensbol.

There are around 31 thousand summer pairs in Britain in the UK and sadly the species is listed as Amber nationally due to recent breeding and winter population and range declines according to BTO BirdFacts, but populations appear to be stable locally in Norfolk and are of least concern in Europe. One study found that populations improved with the addition of dedicated Kestrel breeding boxes so perhaps lack of suitable breeding sites is part of the problem.

We continued to enjoy prolonged, close sightings on the lawn, the pergola and, unfortunately for our small garden birds, the peanut feeder pole at the bottom of our garden for several days in a row, one time mantling on the ground and one time carrying prey to the pergola then feeding.

Perhaps the Kestrel lingered awhile because our wildlife friendly garden offers plenty of small rodents and birds, the Kestrel’s main diet source in Northern Europe, before he moved onwards on his journey.