Grey Squirrels at Glasgow Zoopark

The earliest recorded introduction of Grey squirrels to Great Britain was in 1867 when a pair was liberated at Macclesfield in Cheshire. In Scotland, a pair was liberated at Finnart on Loch Long in 1892, on the borders of Dunbarton and Argyll. From here they spread northwards to Arrochar and Tarbet by 1903, east to Luss by 1904, and to Inverbeg 1906. By 1907, they had spread to Garelochhead, Rosneath 1915, and south to Helensburgh, Alexandria and Cardross by 1912. By 1915 they had spread to the east side of Loch Lomond and Drymen in Stirlingshire.

In 1913 Grey squirrels were introduced to Edinburgh Zoo from where some escaped and colonised Corstorphine Hill, with other introductions at Pittencrieff Park, Dunfermline in 1919 and Ayrshire and North Queensferry in Fife in 1929. These fresh introductions undoubtedly introduced fresh blood, and by the mid-1950s extensive areas of lowland Scotland had been colonised. Where Grey squirrels were not present it was usually because some natural barrier, e.g., a lengthy expanse of treeless moorland, had prevented their immigration.

In the space of about a hundred years, this interesting animal has thoroughly colonised most of Great Britain, with consequences upon the native Red squirrel population which are still being studied and analysed.

We have always had plenty of Grey squirrels, which cause us no problems at all, and are a great delight to visitors. July is a lean month for wild Grey squirrels, with some squirrels dying of starvation before the Autumn harvest, but not here - July is usually our peak month and the visitors leave plenty of scraps which the squirrels enjoy, quite apart from what they can rely on in the animal enclosures.

Glasgow Zoopark maintains a significantly large population of wild grey squirrels focussed on the area around the Tropical House and Children's Farm, down to the Car Parks, and across to the Tiger House, Small Primate House, and spreading out less densely into the Calderpark woodlands alongside the river behind the Ankole Cattle.

The density is in my opinion abnormally high, especially this year where the all year-round supply of zoo food has been boosted by an abundant crop of acorns and hazelnuts, and some beech. As the area described is also visibly part of the former Calderpark Estate and parkland, oak and beech trees are regularly spaced throughout the site.

The favoured zoo food ranges from cubes of bread, some fruit, ungulate, bird and pig pellets, to the most favoured peanuts in their shells, (used as scatter feeds for the Porcupines and Collared Peccaries).

In November, with the young of the year well grown, population levels seem at their highest. This reminded me of South Carolina in 1997 where the area around the Airport on Hilton Head Island seemed to carry a similarly large population. The difference seemed to me that the American squirrels were more dispersed, and clearly feeding on natural foods, particularly the cones of the numerous pine trees. It was also much warmer and the squirrels had thinner coats, suggesting a much lower energy requirement to that of our own squirrels.

What has struck me this year in particular are the high numbers of aggressive interactions amongst our squirrels.

Whilst we have always tried to run the land occupied by the Zoopark (40 acres developed, 95 acres in total) as an ad-hoc nature reserve, I have been well aware - though I could never catch them - that certain locals and one former member of staff regarded grey squirrels as vermin and would shoot them with air-guns - or, so I was told, and certainly that was the way they talked about them.

I would find the occasional dead grey squirrel, usually unmarked, and would assume that it had either been shot by an air-gun, or died of some virus. I confess, I never seriously considered having one post- mortemed.

My purpose for writing is that this year, 1998, I have been very struck by the sheer numbers of aggressive encounters I have witnessed between squirrels. A squirrel bridge highway of a heavy electric cable, crosses a road just outside my office window, joining the building four metres from where I sit. This highway leads directly from one oak tree to another oak tree. Both are positioned in the middle of large enclosures.

I have become very used to the normal vocal communications of grey squirrels and always stop to take a look when I hear a squirrel scolding outside. In the past I assumed this was in response to a cat, and often it was.

However, this year, nearly allof the aggressive scoldings, accompanied by tail flicking, has been emanating from one squirrel chiding another. It can continue for a long time, well over half an hour on some occasions (when this takes place 10 metres away, it takes the form of a stuttering electric drill if you are trying to concentrate). Normally, one squirrel is facing another, who is usually frozen, silent, watching intently from about three metres away. Where they are closer, worst of all when one squirrel has another trapped against the wall with their head close to the masonry, even if you chase them apart, you invariably find a dead squirrel (superficially unmarked) in the immediate area, a day or two later. Killed, it appears again to be unmarked though a tooth through the skull might not leave much visible evidence perhaps?

Was this aggression, as I believe it was, perhaps triggered-off by over-high populations focussed on relatively concentrated feeding points? Or, was the second squirrel already ill in some way, and in consequence being singled out by the others?