The Black Death – try an eco-remedy

Cormorant - a skilled fisherman that avoids paying the entrance fee, East Warwick gulls, Eider!

I was once escorted out of a fishery conference for suggesting that anglers use Cormorants as a scapegoat for bad fishery management. A trip down to Walthamstow Reservoirs reminded me of the Cormorant-fish controversy, the bird anglers like to call the ‘Black Death’ and claim wipes out fish stocks. Now there is some truth to this complaint in some situations – on many a simple fishery, the Cormorants will be able to simply catch the fish without much effort.  Surely it wasn’t the clearest of thinking to establish a trout fishery on a concrete puddle that had a Cormorant roost in the middle!  Despite this, situations are not always as clear as they seem; most Cormorants nesting at Walthamstow do not fish on site.  I’ve always believed that birders and anglers should be on the same side – we both want to see healthy wetlands.  And the starting point for a solution should be to look at these healthy natural wetlands, particularly the complexity of the underwater habitat.  Provide fish with refuge areas and they will be less easy to catch.  Variation in the topography of the lake bottom, the addition of underwater reefs in the form of fallen trees, rocks or islands of aquatic vegetation, have all been shown to help. These are standard measures that conservationists will employ in creating a new wetland.  But instead of improving fish habitat, the average fishery manager too often rushes for the shotgun and chainsaw.

A second issue at Walthamstow is the apparent decline of breeding duck. In what seemed a good idea at the time (Thames Water have a history of good conservation staff), the formerly scrubby island on the East Warwick was cleared and re-formed, in order to try and create a better habitat for waders and duck. Unfortunately, this did not foresee the surge inland of breeding Herring and Lesser Black-backed Gulls. The gulls took over the island, the duck departed. Predation by the gulls has clearly changed the distribution of breeding duck. Good management of the islands and marginal vegetation would seem to be central to solving the problem.

I first went to Walthamstow Reservoirs exactly 40 years ago. I missed a Shag, but got quite excited by a pair of Goldeneye. There were no roosting Cormorants (this started in 1972 I seem to remember). The first Trout went into No 5 in 1978. Today there were plenty of Cormorants (at least 142 active nests), 7 Ring-necked Parakeets and an Eider.

How big are your tussocks?

Brents at Old Hall - keep eating chaps.  Spot the Brant.

The ‘improved’ grass fields at Old Hall Marshes are managed to provide winter grazing for the internationally important numbers of Dark-bellied Brent Geese in the Blackwater Estuary. The fields are prepared to provide the lush sward of fine grasses the birds prefer to eat, with a target grass height of 50-100mm in October. The ‘by-product’ of a winter's grazing by geese and Wigeon is a tight, occasionally tussocky, short spring grassland that attracts nesting Lapwings. However, in recent years, Brent numbers locally have followed the national trend of decline. There has been less grazing in the fields, resulting in a spring grass height somewhat longer and poorer for Lapwings.

Today the sward measuring boots had an outing to the various fields at Old Hall. With reduced grazing and warmer winters, additional grazing may now be required to bring the spring sward into an ideal condition. Formerly fertilised, farm-yard manure is now added to the fields; the Dutch traditionally do this in late winter to bring earthworms towards the surface for the benefit of breeding waders such as Black-tailed Godwits.

Around 3,500 Brents have been using Old Hall of late, with around 18% of young birds suggesting a good breeding season in 2010. The flocks of Dark-bellied Brent today also harboured a Black Brant and a Pale-bellied Brent. Six white-fronted Geese were nearby. Displaying Marsh Harriers were continually in the air (up to 10 birds together), and Merlin, Peregrine, a couple of Ruff, Pintail, Scaup, Bearded Tit and a few of the recently recorded 1,800 Grey Plovers were amongst the mass of birds on offer today.

B-n G's

The William Girling - a bit like the sea but without sand, or salt, or sun, or birds (except B-n G's).

The William Girling Reservoir holds the largest wintering group of Black-necked Grebes in the UK. Yet this is not a bird-rich site. It is not especially favoured by diving duck, it is shunned by Shoveler, poo-pooed by Pochard and used principally as a dormitory by dabblers.  It is a concrete doughnut holding water.  But presumably the B-n G’s have some competitive edge here. Although there are occasional records from other sites in the Lee Valley, no other local site regularly holds wintering birds. The peak count on the Girling over the last ten years was of 32 birds in December 2007. Peak winter numbers have been around the mid-20s for the last three winters.

With 24 birds arriving on the reservoir in the first week of August last year, around this number of birds have remained all winter. Numbers are just beginning to drop as the first birds move off, 18 were still present today. Seven months on the Girling! What is there left to eat?

Black-necked Grebes are a specialised invertebrate feeder, principally seeking aquatic insects and their larvae by ‘gleaning’, although they may also take molluscs, crustaceans and small fish. They tend to favour shallower waters in the summer, moving to deeper, mainly coastal sites in winter. This concrete-edged basin with water depth of around 14 metres would seem to be at their edge of tolerance, with BWP stating diving depths of up to 5.5 metres for up to 50 seconds. Birds diving around the margins (where there are concrete ‘roads’ a metre or so down) stay under for 30-40 seconds, whilst those well away from the reservoir margins re-surfaced after 50-60 seconds. It would be fascinating to find out what they are feeding on. The other big question is where are they between February and August?

Target: higher water levels

Spring seemed just around the corner today, with glorious sunshine at last and reports of booming Bitterns coming in from the south-west.  So, with a trip down to Rainham Marshes, thoughts turned to maintaining ideal water levels through the coming breeding season.

A lot of work is happening at Rainham this winter, not least a review of the hydrology. Maintaining adequate water into the summer is a key issue; essential for providing good feeding conditions for breeding and passage birds.  Good work by the site staff over the winter has blocked some of the seepage points identified last autumn. The Target Pools look particularly good at the moment, with higher than usual water levels – but the test will come in the spring as water levels naturally drop. The overall aim should be to achieve a strategic approach to water level management, a succession of good feeding areas around the reserve through the year. Various trials involving moving water around the site should indicate if this is possible.

Yesterday's Penduline Tits failed to re-appear, but with good water levels the reserve was holding large numbers of birds, notably Lapwings, Wigeon and Teal, and of course gulls.  Meanwhile, back on the garden feeders, Mealies continue to feature; up to six amongst the 20+ redpolls.