Wednesday, 27 May 2015

Havergate Island - adapting to climate change

When the tidal surge of December 2013 hit Suffolk, 1.5 million cubic metres of water poured over the sea walls into Havergate Island, flooding everything bar the tops of the hides and huts.  It is widely acknowledged that the flooding of the island saved other land around the estuary from a similar fate.  Damage was severe to some parts of the walls and it took a month or so to drain out the water to suitable levels. But ultimately, the flooding caused very little damage to the ecology of the island and may even have been beneficial.  Under climate change predictions, such events will increase in the coming years.  So where do we go with Havergate in the future?

Havergate Island used to be 'Avocet Island' but although large numbers of Avocets still feed on the lagoons, very few now breed.  In recent years the complex of saline lagoons on the island have been colonised by 1000s of pairs of Lesser Black-backed and Herring Gulls.  Now, nice as large gulls are, they have the potential to all but eliminate smaller 'seabirds' (gulls, terns and waders) by their sheer density of occupation and their habit of predating the chicks. Whereas 20,000+ pairs of LBBG used to nest in the adjacent Orfordness, a rapid decline to just a few hundred has occurred due to predation by Foxes and disturbance.  Evidence from colour-ringed birds shows that these displaced Orfordness gulls now nest widely.   There were 2,070 pairs on Havergate in 2014. Although the gulls may be squeezing out the Avocets, the island is still favoured by Spoonbills and in other locations they are quite happy to nest amongst large gulls.

The surge tide damage to the island has now been repaired. The section of wall that was all but washed away has been re-built but is now slightly lower and re-profiled.  The aim is to lower and re-profile further sections of wall and install more water control sluices.  The lowering and re-profiling will allow future surge tides to flow in more smoothly without damaging the walls, so will both reduce repair work and maintain the wider flood defence benefits of allowing the island to flood.  The additional sluices will allow quicker discharge of the floodwater to restore optimum water levels.  The island will be managed for wintering and passage waterbirds, breeding gulls, Spoonbills and specialist lagoonal invertebrates such as the Starlet Sea-anemone.  But what of the displaced Avocets?

On the ‘mainland’ of Suffolk the aim is to ‘roll back’ and create new freshwater and brackish lagoon habitat behind the seawall.  The project at Hollesley (as previously described) is already highly productive for breeding Avocets and other waders.  New areas are also being planned at nearby Boyton to add to the existing wet grassland habitat.  The aim is to adapt to climate change, where possible providing benefits both for wildlife and for people at the same time.

Photos: above: Havergate aerial, just after the surge, Avocets in a fluster.
Below: damaged sea wall, Starlet Sea-anemone, Hollesley aerial.

Saturday, 16 May 2015

Thinking Dutch on flood defence

The Dutch think big! Why can’t we do the same?  A short trip over to The Netherlands for a meeting with the Dutch Birdlife partner Vogelbescherming Nederland (VBN) was a suitable excuse for a couple of site visits. First on the itinerary was a Black-tailed Godwit hotspot at Eemland where 200+ pairs nest on a typically open, wet meadow habitat.  Godwits are increasingly restricted to nature reserves where high water levels are maintained and this reserve is a great example of management for meadow birds.

Continuing north, we came to our main destination outside of the town of Groningen where a massive total of 3,000 ha of wetland habitat has been created as a flood defence scheme for the town.  The waters of the local rivers flow north towards the Wadden Sea.  Historically the low areas around Groningen supported a large peat bog habitat.  Attempts to drain the area started in the Middle Ages and the last 100 years has seen the area managed as pasture.  However, Groningen has a history of serious flooding when river levels have been high.  The local water board Noorderzijlvest looked for a flood defence area, a 'washland', in order to protect the town.  They concluded that the area to the south west of Groningen called De Onlanden area was most suited to fit their requirements. The area was mainly under the control of farmers or conservation organizations. A partnership of organisations was formed and in 2009 the new flood defence scheme was initiated. 

There are two main areas that we looked at: De Onlanden and an area near Zuidlaardermere.  Flood waters are stored in these areas to various depths of up to 1m.  How is this different from washlands in the UK? The key factor is there is an agreement that a level of water is retained into the spring, creating fen, reed and open water habitats.  This brings a win-win situation; flood storage and wildlife-rich wetland habitat. And wow, is this a win for wildlife. 250+ pairs of Black-necked Grebes, breeding Whiskered and White-winged Black Terns, 16 booming Bitterns, Corncrake, Baillon’s, Little and Spotted Crake, 120 prs of Bluethroat, 100prs of Grasshopper Warblers and 150 prs of Marsh Warbler. But this area is not just for wildlife; it is now extensively used by local people for cycling, walking, fishing etc.

In the UK we have numerous washlands, but none deliver like De Onlanden, ours are drained down in the name of maintaining storage capacity. Why can’t we think big and imaginatively like the Dutch?

Tuesday, 5 May 2015

Great Knot

Chongming Dongtan is an important stopover point for migrating Great Knot. The Great Knot is a long distance migrant that uses a limited number of stopover sites between the wintering sites in Australia and the Russian breeding areas. The Great Knot is also a wader that is in some trouble; numbers have declined sharply in recent years. Habitat loss and degradation, hunting, lack of food and pollution all form potentially significant threats.  Students from Fudan University have been studying Great Knot to understand their migration strategy. This year, birds are being radio-tagged and leg-flagged at Chongming.  The birds are caught by ex-hunters sat out on the tidal flats who whistle the birds down to a clap net.  Remarkable stuff.

Studies have shown that many Great Knot undertake a long flight straight from Australia to the north Yellow Sea, with varying numbers stopping off at Chongming before completing the short hop up to the north Yellow Sea.  This may largely depend on weather conditions. Birds may stay at Chongming just a day, or for up to 2 weeks, again largely dependent on weather. This is reversed in the autumn, with a long flight south from Chongming.  Studies show that birds attain a significantly higher body weight at Chongming Dongtan during the southward than northward migration. The Fudan University team are also stationed on the Chinese/Korean border to await northward-bound radio-tagged birds. Birds have been recorded arriving the day after leaving Chongming.

The diet of the Great Knot is mainly bivalve molluscs, gastropods, polychaete worms, crabs and shrimps.  At Chongming the main food is the small gastropod Assiminea violacea and the clam Corbicula fluminea; beasts of brackish waters that like the mudflats towards the mouth of the Yangtze. These two can form 70% of the diet of Great Knot at Chongming and are critical to its migration strategy.

Photos: above: Great Knot, clap-netting, fitting radio-tags and leg-flags.
Below: bird with radio-tag, autumn Great Knot, food!, shell-fish gatherer.