A change in habitat decimates butterfly site


After last week’s account of my battles with the local crows to try and keep my bird feeders more small-bird friendly, several of you wrote to say that I’m not the only one with that problem.

The most popular means of deterrent seems to be an ingenious combination of wire netting of different mesh sizes wrapped around the feeders to allow small birds to enter, leaving the crows and feral pigeons gnashing their beaks in frustration.

I also mentioned that I had an unusual visitor in my back garden in the shape of a rare northern brown argus butterfly, which is normally found in a more upland habitat.

I was walking in just such a place at the weekend and was delighted to find a small colony, many of which were on the wing, in between the heavy thundery showers.

I was in a small glen which is an offshoot of the main Yarrow valley and was once a brilliant site for butterflies.

Previously on warm summer days, there were hordes of things like meadow brown, ringlet, common blue, dark green fritillary, small tortoiseshell, peacock, red admiral, small heath, small copper, not to mention the various whites, all on the wing.

Other than the aforementioned northern brown argus, I only saw a few ringlets, small heaths and one small copper.

Why should this be?

The answer is simple – habitat change. A few decades ago, the glen was heavily grazed by sheep, which kept the scrub encroachment to a minimum and the bracken was managed.

This allowed plants such as thyme and rock rose to thrive on the sunny slopes. These species in turn were important food plants for the butterflies.

The valley was sold for forestry and although the bulk of the glen was planted sympathetically with native broadleaved trees, the sheep were removed. Once the scrub and bracken began to return, the butterflies’ food plants were shaded out and soon disappeared.

Not only that, but the many ant hills in the area, which depend on grazing to keep the inside temperature stable, also died out, taking with them things like the green woodpecker, which is mainly an ant eater.

The place is very different now to when I used to visit. The once-bare hills are now covered in mainly hawthorn scrub and the rough grassland of the valley floor is rapidly becoming woodland.

Although I think that in the past the place was heavily overgrazed, to remove it completely has had dire consequences for many rare species of wildlife.

As with most things in life, there is always a happy medium.

You can email me your pictures and sightings of Borders wildlife at corbie@homecall.co.uk