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

An Aberration!

View fullsize

A Small Tortoiseshell aberration semiichnusoides butterfly showing merged costal black spots and white marginal streaks instead of blue studs on the forewing and missing the orange band on the hindwings

Our hot late June summer weather didnt last too long, and perhaps could be deemed an aberration in its own right, but it also seems to have had a major impact on our caterpillars while they metamorphosed into butterflies.

I got curious when I spotted this unusually marked Small Tortoiseshell butterfly and discovered a strange world of genetics and temperature driven body chemistry!

It takes about 4 weeks for a caterpillar to metamorphose into an adult butterfly in a fascinating “black box” process that science still knows surprisingly little about.

The term for a butterfly with these atypical variations in markings is “an aberration”, which stems from the latin aberrationem, literally meaning “a wandering”. First used in the 1590s, the modern meaning of “a deviation from the normal type” is attested by 1735.

It turns out that both genetics and abnormal weather (and perhaps even the two in combination) can play a role in triggering these deviations. Aberrations are caused when something interrupts the usual pattern of markings during their development inside the butterfly’s chrysalis. One hypothesis is that sudden temperature “shocks” (in either direction) may trigger melanin release (a dark pigment) to increase or decrease.

Another possibility is the activation of rare inherited “recessive” DNA genes (a gene that requires both parents to have it to be activated) that are atypical because they hinder the chances of an individual finding a mate, or even surviving under normal conditions. They continue however to be carried in the population because they may perhaps aid survival in abnormal conditions.

One example of this is the better known aberration - the dark brown“Valezina” form of the Silver-washed fritillary quite often seen now at Holt at Foxley Woods. Valezina, due to its dark colouration is more able to fly and find nectar in unusually cool temperatures than its typical bright orange counterpart, but which may then be at a disadvantage when it comes to finding a mate and reproducing due to being less readily recognised.

Whether the sudden temperature change we saw at the end of June activated a dormant gene relating to surviving with abnormal weather or coincidentally acted directly on melanin production remains one of the fascinating mysteries of nature.

Small Tortoiseshell Aglais urticae (normal type) vs Small Tortoiseshell (aberration semiichnusoides). Both butterflies are likely to be siblings as they were hosted as caterpillars on my nettle bed and appeared fresh on the same day together.

Resources and References

“Variation in British Butterflies” by Peter Eeles, Dispar magazine

British Butterfly Aberrations - Reference Website

Poppies, Poppies, Poppies

At last! Some beautiful, warm, sunny summery days.

Lately I've become totally obsessed by the fleeting, ephemeral nature of some beautiful red Common Poppies, Papaver rhoeas, that have sprung up by the new patio due to earth disturbance.

The Poppy’s flower buds burst open first thing but are so fleeting they only last a single morning. Their nectar banquet must be intense as pollinators such as bumblebees and hoverflies go wild over them.

Through the course of the morning the delicate Common Poppy petals steadily fold further and further back until they fall to the ground, or are knocked off by the weight of frantic bees trying to land. This all happens in the space of a few hours and by early afternoon the blooms are already gone, petals lying crumpled and shriveled up on the ground.

Rainbows and Barn Owls

It's been a long hard slog through to spring, but this weekend I was gifted with a beautiful Barn owl sighting right from my garden gate.

I'd popped out to try to see a rainbow that my husband mentioned spotting, when from the corner of my eye glimpsed two lazy wings as he finished quartering the field opposite my house and perched up for a breather.

When I turned around the rainbow was fading rapidly with the sun and each of the colours was imbued with a soft peach hue. A beautiful moment of tranquility.

View fullsize