Maybe Sheffield's herons are doing a conservation task and keeping the crayfish under control

Walking through the Moss Valley woodlands in recent weeks the grey herons have beenshowing quite well and regularly too.

Thursday, 6th May 2021, 6:00 am
A grey heron in Long Wood

We see them overhead flying from Oakes Park to Graves Park ponds but down in the woods they have been less frequent. This year however, the herons are clearly stalking the woodland streams; and this does make me wonder what they are hunting for. I doubt there are many fish in these waters and they virtually dry-up in the summer. They will certainly take frogs but this year their numbers seem to be down too.

Moss Valley and the Moss Brook were once well-known for their population of the now almost extinct native crayfish which have been displaced by competition and disease associated with the invasive, North American signal crayfish.

Certainly the streamside banks have plenty of holes which could well be signal crayfish burrows; one of the crayfish impacts being erosion and de-stabilisation of soft banks. So maybe the herons are doing a conservation task and helping keep the crayfish numbers under control.

The upper Moss Valley also has remarkably intact ancient meanders of the streams through its woodlands and this is unusual too. Very often woodland cover close to streams and rivers has been cleared for farming and the channels are straightened too. Deep in the woods the grey herons look almost primeval and with a heady fragrance of bluebells and wild garlic, they add to the atmosphere of the unique ancient woods. Where the streamsides are down

in the bottoms of small valleys and the footpaths skirt the higher levels only, then these magnificent birds at least have a degree of protection from disturbance. They will be nesting reasonably close by as well and usually, but not always, in high treetops and communally.

The heron is yet another bird which took a tumble because of pesticide pollution, habitat loss with wetland drainage, and of course persecution. Since their all-time low in the 1970s, herons have recovered dramatically and this is in no small part due to reduced pollution in rivers and streams.