Weather for ducks

Until the recent deluge, it appeared that another dry spring was upon us and the focus of reserve visits recently has been on the efficiency of water management.  Although concerns about the effects of the drought on wetlands and wetland birds have been somewhat over-hyped, it is certainly worth thinking about how we manage our water resources, particularly in relation to changing climatic patterns into the future.  On many sites, water is simply allowed to drain away; maybe not a problem in a wet year, but in a dry year perhaps making the difference between a poor and reasonable breeding season.

Visits to Old Hall Marshes and the Ouse Washes were on the agenda for last week.   Both are tremendous sites for waders but they face differing issues.    Old Hall is located in one of the driest parts of the country and frequently struggles to maintain enough water, whilst the Ouse Washes have been suffering from excessive summer flooding in recent years.   At Old Hall, a total of around 250 pairs of Redshank, Lapwing and Avocet breed.  It is also a great site for passage and wintering waders, although the day I visited was not the best; a couple of Spotted Redshanks, 30+ Whimbrel, 50+ Black-tailed Godwits, Ruff and LRP.  Summer migrants were represented by a few Common and Arctic Terns while the last couple of dozen wintering Brent Geese were still on the saltmarsh.  The Ouse Washes support around 500 pairs of waders, notably 140 pairs of Snipe.  Plenty of drumming birds were evident on my visit with added interest provided by Garganey, Ruff and Black-tailed Godwits.

Where water availability is a problem, the key to success is a clear understanding of the water budget – the annual inputs and outgoings.  The annual rainfall at Old Hall is a meagre 577 mm, with a mean summer moisture deficit of 110mm.  So, all available excess winter water has to be stored to offset summer losses through evaporation and transpiration.   Excess water is taken from the Salcotstone Brook which flows through the reserve and out into the estuary.   The water is stored in the fleets, borrow-dykes and reedbed, with wind pumps moving this water into the key wader areas as required.  Breeding wader areas may be allowed to dry from July onwards but areas such as Bale Field and Pennyhole Bottom require water into the autumn wader passage.  Old Hall remains below target water level this spring, so the recent rain is welcome.  By contrast, the Ouse Washes were looking superb in the ‘drought’.  After the weekend’s rain, the site is flooded bank to bank.  Good for ducks, not so good for waders.

Titterel time

A long look around Old Hall Marshes shows this reserve to be in good shape. Old Hall retains extensive areas of old coastal grazing marsh by the Blackwater Estuary. Grazing of these ancient marshes, since their enclosure in the Middle Ages, has created a characteristic undulating landscape, with the channels of the old saltmarsh creeks still evident. The ant hills of the Yellow Meadow Ant, estimated to number in excess of 500,000, give credence to the antiquity and uniqueness of this landscape.

The variable topography of the grazing marsh, combined with a carefully manipulated water table and grazing regime, creates a fleet-type habitat ideal for breeding waders and duck: the depressions formed by the old creeks and salt pans retain water, while the tall, aquatic vegetation and tussocky grazing marsh sward provide nesting cover. Around 100 pairs each of Redshank and Lapwing nest, along with numerous Pochard, Shoveler, Tufted Duck and Gadwall. This is undoubtedly the best site of its type in Essex.

Old Hall is also highly important for passage waterbirds and a visit in late April/early May is virtually guaranteed to produce at least a few Whimbrel (locally known as Titterel in the past). My visit produced a respectable 87, although spring peak counts in recent years have reached 250, making Old Hall an important site nationally for this species. With the scrape on Bale Field in excellent condition, the day’s wader list amounted to 19 species, including single Little Stint, Curlew Sandpiper and Wood Sandpiper, and several Spotted Redshank and Greenshanks.

A year back, I blogged about the Avocets at Old Hall. Well, last year they did well, with 59 pairs on Irongate rearing 50+ chicks. Good numbers appear to be settling this year also. The Avocets moved to Irongate following erosion of the nesting islands on the brackish lagoon at Pennyhole Bottom. These have been restored, and with further work to come, should provide an alternative nesting site, and be in good condition to host autumn passage waders. It’s a long walk around the 11.5 km of seawalls, but there are birds at every turn.

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.

13th May. Old Hall

With 54 pairs sitting on eggs at Old Hall Marshes it might look as if this is going to be a good year for Avocets. But how many will make it through to fledging? If recent years are anything to go by, then very few. When Avocets first colonise a site they typically are very productive but as the years go by, fledging success falls away even if the number of breeding pairs continues to increase. This has been the case at Old Hall, and at many other well known Avocet sites. Some studies show food availability as the key factor, and we know that at Old Hall last year, the average biomass of Avocet food items in the pools was only a small fraction of the recommended level. So this might be the reason. However, we also know that predation is another major factor. Avocet chicks are gobbled up by a variety of predators, not least gulls and foxes.

Whilst both these factors are probably playing a part, the broader issue is that Avocets are an ‘early successional’ species, turning up and doing well at new sites before the habitat matures and brings in other species, such as gulls, or the site productivity (in terms of food availability) drops, or the predators get to know where their dinner is likely to be located. Maintaining Avocets on a small ‘stable’ nature reserve can be difficult, and involve much scratching of heads.

Whilst in such a bout of head scratching at Old Hall, we enjoyed 3 Spoonbills, 35 Whimbrel, 2 Greenshanks, 2 hunting Barn Owls (one catching a vole), 6 or more Marsh Harriers, 2 newly fledged broods of Bearded Tits, and watched the first hatching Avocet chicks. How many will survive this year?