Thursday, 10 November 2011

Old and new

It’s interesting to compare sites and over the last week I’ve looked at the development of some new sites and the problems on some old ones.  The new included the still rather raw Frampton Marsh in Lincolnshire, where the scrape habitats, once fully functioning, promise to be amongst the best in the country.  A murky day delivered a Black Brant amongst hundreds of Brents, a Great Grey Shrike, Hen Harrier, Blackbirds and Fieldfares dropping in from a grey sky, and a plate of Blewits for supper.  A day later, the early signs of a diverse habitat of reedbed and heathland were evident at Snape in Suffolk, with young, vigorous reed romping across the re-wetted valley.  The old sites included North Warren, where a Dusky Warbler tacked away in the bushes and the first White-fronted Geese of the autumn dropped in, and, a few days previously, Leighton Moss in Lancashire, where my undoubted highlight was a Great White Egret flying behind a Marsh Harrier circling over a feeding Otter, although roosting waders on the saltmarsh pools was not far behind.

The loss of breeding Bitterns from the reedbed at Leighton Moss has been a cause of some concern and debate.  The fundamental problem at Leighton (for Bitterns at least) is that it is an ageing reedbed.  Reed die-back around the meres has been noted for many years, with a recent replacement by Reedmace.  Reed die-back is a well known issue in older reedbeds, resulting in poor quality reed with a low genetic diversity. The formation of toxic by-products by the reed litter under anoxic conditions reduces shoot density and vigour.  Reed re-colonisation into anoxic sediments is also known to be poor. At Leighton, the grazing effects of both moulting Greylags and numerous Red Deer are likely to be a significant contributory factor.

We know that fish biomass is way above the accepted threshold levels for Bitterns and that eels are as abundant as at any site.  The site supports several wintering birds yet the one remaining boomer is of poor quality and a late starter.  This all strongly suggests that a lack of fish availability in the reed/water interface is preventing birds reaching breeding condition, with a lack of secure nesting sites due to the drier conditions an additional problem for Bitterns.

However, Leighton Moss remains a superb wetland habitat with a high species diversity.  Old age results in one or two little grumbles but overall the quality shines through.