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Old Hall Marshes
Around 5% of the UK avocet population nests on the 17 ha lagoon at RSPB Old Hall Marshes nature reserve, which also has nationally important numbers of ruffs during migration.
The threats to the lagoon and its birds include a potential shortage of water during very dry weather, leading to a shortage of food for avocets and their chicks. Low organic content in the lagoon bed causes a reduction in the biomass of invertebrate prey available to avocets.
Meanwhile sea club-rush, Bolboschoenus maritimus, invades open water, reducing the area of the lagoon. Nesting islands can suffer from vegetation growth and erosion can also damage them. Predation, especially by foxes, is a major threat.
Actions to address threats
A cattle-proof fence has been erected to allow grazing of the lagoon margins, which controls vegetation encroachment, adds organic matter and improves penetrability of substrate through hoof action.
Viewing screens and paths have been designed to allow people to view the lagoon without disturbing the wildlife
The lagoon bed is rotovated in autumn before re-flooding to break up the surface pan.
Water levels are reduced each spring to provide feeding areas and expose nesting islands for avocets. When there is a lack of water, it can be pulsed into the lagoon from the dyke system.
The islands are maintained mechanically to remove vegetation, although in some years the vegetation is suppressed by inundation during high winter water levels
Viewing screens and paths have been designed to allow people to view the lagoon without disturbing the wildlife.
Bird and invertebrate populations are monitored annually, and organic content and penetrability of substrate are monitored biannually. Salinity and water levels are monitored monthly.