Jays take flight from roving squirrels

LAST WEEK I wrote an article on this page about jays. I noted that jays were more numerous in the south and east of the country but that the pattern seemed to be changing, with the population slowly shifting north westwards.

My source for this information was David Cabot’s excellent book Irish Birds. In it he writes: “The jay has apparently been extending its range northwards and westwards since the beginning of the century, while becoming scarcer in the south-east, where its absence from suitable breeding habitats is difficult to explain.”

Although my copy of the book is dated 2004 the first edition came out in 1995, so I was pretty sure that the century he was referring to was the 20th not the 21st .

When it comes to natural history I love a mystery. It might be difficult to explain, but there had to be a reason why a bird like the jay, which has lived in Ireland for thousands of years, had decided to move north westwards in the 20th century. The problem niggled away at the back of my mind.

At first I tried to reconcile the population shift with changing patterns of forestation, but this didn’t seem to work very well. Then my eureka-moment arrived just before I fell asleep one night. I sat up in bed and said ‘squirrels’ in a loud voice, which my wife thought was fairly peculiar.

As most people know, the grey squirrel was introduced into Ireland in 1911. Soon afterwards ornithologists noted the start of a population movement in jays.

The squirrel introduction was on the shores of Lough Forbes in Co Longford which is actually a wide part of the River Shannon. The squirrels multiplied very rapidly but they moved in a southerly and easterly direction. Even today there are practically no records of them west of the Shannon. The only exception to this is a small number in the extreme north-west of the country where they seem to have managed to get around the top of the river.

Why they have found the river such an insurmountable barrier is also a bit of a mystery. Some zoologists have suggested that grey squirrels are more susceptible to being preyed on by pine martens than reds are and that the higher population of pine martens west of the Shannon may be keeping them at bay.

But grey squirrels also have a different diet to red squirrels and different habitat preferences. Greys prefer to eat the seeds of broadleaved trees while reds prefer cones. A red, for example cannot physically digest an acorn while a grey can.

Jays can eat cones and there are populations of them in purely coniferous plantations in Co Wicklow. But they prefer broadleaved woodland, or mixed woodland, and they like to have access to things like acorns, ash keys, hazel nuts and beech mast.

My theory of what happened is that as the grey squirrels colonised the south and east of the country they became a new competitor for jays in their traditional Irish range. There may also have been some direct predation because grey squirrels eat the eggs and young of birds. Jays do this too, but I don’t think they were a match for this new, large squirrel from north America.

But jays can fly and squirrels can’t so the broad River Shannon was no barrier to the birds. They simply shifted northwards and westwards where the only squirrels were the little red ones, which they found much easier to live with.

I must admit that I’m rather pleased with my new theory, but it is, of course, only a theory. Now I’m trying to work out some way of verifying it, either experimentally or through field studies. Has anyone any ideas?

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