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Minsmere
The artificial coastal lagoons are known as the Scrape.
They support nationally important breeding populations of avocets (21%) and little terns, Sterna albifrons (1%). Important populations of lapwings, Vanellus vanellus, redshanks, Tringa totanus, and common terns, Sterna hirundo, also nest. The Scrape is also nationally important for an assemblage of wintering and passage waterfowl.
Vegetation encroaches into the shallow open water margins that are favoured by feeding birds, and onto the nesting islands. The balance of salinity levels is important for building a large biomass of invertebrates for the avocets to feed on, but periodic droughts and high rainfall make this difficult.
Low freshwater flows cause increases in salinity levels in the lagoons, whereas excess rainfall causes freshwater levels that are too high to add sea water, leading to low salinity levels, both situations affect the invertebrate populations. Predation of eggs and young of ground nesting birds is also a problem.
Actions to address threats
The main project has been to expand the North Girder lagoon by 2.5 ha, restoring it to its original size. The extension of the lagoon was excavated, and water carrier ditches re-dug using a tracked 360-degree excavator. The material dug out has been used to create linear islands within the lagoon and to improve perimeter bunds.
The islands are designed to attract breeding avocets, but being narrow should deter nesting black-headed gulls, which potentially disturb the avocets and predate their chicks. The islands radiate from the viewing hides, so enhance birdwatching. During the works, four new water control pipes were installed to allow fine scale management of water levels and salinity levels within the lagoon.
A 3.7 km anti-predator fence surrounds the lagoons to protect nesting birds from ground predators. This had become old replacement was cheaper than continual maintenance and provided an opportunity to improve the design. The new fence is adjacent to a wet ditch, so predators have to swim the ditch before trying to jump the fence with no run-up. The new fence is also lower, so less visually intrusive.
Regular management work
Vegetation is cut on the banks, islands and lagoon margins in autumn to maintain open views from the hides and prevent encroachment. Island vegetation is cut as low as possible in March to be ready for the bird nesting season.
Marginal vegetation is cut underwater to limit its regrowth.
Water levels and salinity levels are manipulated.
The anti-predator electric fence is checked and maintained throughout the breeding season.
Public awareness and information
A full events programme is run throughout the year. East Hide has been replaced with a double-decker hide with capacity for 40 visitors. Public trails around the lagoon have been upgraded to meet new disability standards, allowing access to hides by wheelchair.
Survey and monitoring
Scientific monitoring of lagoon invertebrates has shown that reduced salinity levels caused by excess winter rainfall have reduced the biomass in East Scrape. These are expected to recover as salinity levels stabilise following recovery after the works.
The five-year average number of avocet nests is 101, but productivity is low. Periods of low food availability and predation by gulls are the main problems, and poor summer weather takes a toll. Conversely, the numbers of lapwings nesting on the Scrape are at the highest ever. Other breeding waders, gulls, and terns are also doing well.