Monday, 30 April 2012

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.

Monday, 23 April 2012

Philopatry? – no thanks, there’s a drought.

A stilt in Donana - coming to a site near you

Having recently moved home and been starved of internet access, birding and blogging has recently been on the back burner.  However, the arrival of a few Black-winged Stilts in the UK links nicely to my last entry.  Further to the exodus of Glossy Ibis from Donana due to drought in the region, it is likely that, given a fair wind, this spring will also see a bumper crop of Black-winged Stilt sightings in the UK.  The breeding population of stilts in Donana varies from around 50 pairs in dry springs to over 14,000 pairs in wet years.  The North Atlantic Oscillation (NAO) is one of the main cyclical climatic forces that affects the weather of the region.  During positive phases of the NAO, westerly winds increase temperature and rainfall over northern Europe but bring drought to the Mediterranean.  Stilts will normally return to breed at their natal site but when conditions are poor, dispersive  behaviour kicks in and they move north.  A study by Jordi Figuerola showed a clear link between poorer conditions and less breeding birds in Donana and the number of records of stilts in the UK.

Drought is much in the news at the moment.  The wildlife stories are all doom and gloom.  Yet wildlife adapts to such conditions as shown by the ibis and stilts, and such dispersive behaviour will prompt colonisation of new areas.  The drying of the Oostvaardersplassen in The Netherlands in the 1990s resulted in the dispersal of the locally breeding Spoonbills and colonising many new areas.  What’s the odds on Black-winged Stilts breeding in the UK this year?