Norfolk Hawker (Aeshna isosceles) (Müller 1767) - Species Action Plan

Norfolk Hawker is a large, gingery-brown dragonfly with conspicuous green eyes. It has largely clear wings, two yellow bands on each side of the thorax and a yellow triangle on segment 2 of the abdomen. Adults fly from May to August, but are most numerous in June and early July. Eggs are laid into living plant material below the water surface and hatch after three to four weeks. Larvae develop over two years. Norfolk Hawker Dragonfly Photo
(Photo credit: George Taylor)
Ref  2/S27 Species Action Plan 27
Plan Author: British Dragonfly Society (BDS)
Plan Co-ordinator: Waterbodies BAP Topic Group
Plan Leader: BDS
Final Version 25 March 2010
Plan Duration Five Years

Action Plan Summary

Current Status

National Status

Norfolk Hawker is a dragonfly that breeds in fen and grazing marsh dyke systems in east Norfolk and east Suffolk. It inhabits unpolluted ditches and dykes, and occasionally small turf ponds. It requires clean water, a rich aquatic flora and sufficient terrestrial space to hunt. In England, it is particularly associated with, although not totally dependent on, a rich aquatic flora that includes abundant Water Soldier Stratiotes aloides.

Globally, Norfolk Hawker is a Mediterranean species that is widely distributed in lowland areas of Southern and Central Europe. It is classified as Vulnerable in the North African Red List and is absent from Scandinavia, with the exception of Gotland.

In England, Norfolk Hawker has always been a scarce and local insect, although there are small pockets of relative abundance. Historically, the species was also found in the Cambridgeshire fens, but the last reliably dated record from the Fens was taken in 1893.

Since 1990, Norfolk Hawker has been regularly recorded from a maximum of eighteen 10km squares in Norfolk and east Suffolk. The largest populations are found in the Broads and in the marshes that border the eastern end of the River Waveney. There is a population in Suffolk centred on Minsmere and Sizewell. Further 10km square records in both counties and beyond are the result of wandering migrants or accidently and thus artificially transported larvae.

Norfolk Hawker has full protection under Schedule 5 of the Wildlife and Countryside Act 1981 (as amended) and is listed in section 41 of the NERC Act 2006. It was included on the national BAP list (2007) and is listed as Endangered in the Odonata Red Data List (2008).

Norfolk Status

Seven of the eight river valley systems or waterbody areas currently occupied by Norfolk Hawker are in east Norfolk, with the majority in the Norfolk Broads. The eighth location is in east Suffolk, on coastal marshes in the Minsmere/Sizewell area. Therefore, the majority of breeding sites for this species are within Norfolk.

Norfolk river valleys or waterbody systems supporting Norfolk Hawker populations are listed below:

  • River Ant, including marshes adjacent to Alderfen, Barton and Sutton Broads;
  • River Bure, including marshes adjacent to Ranworth Broad and Upton Marshes;
  • River Thurne, including marshes at Horsey Mere, Hickling and Martham Broads;
  • Trinity Broads and surrounding marshes;
  • Halvergate and Acle (Damgate) marshes;
  • River Yare, including Wheatfen and Strumpshaw Fen;
  • River Waveney downstream of Bungay.

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Current factors causing loss or decline in Norfolk

  • Penetration of saltwater into grazing marshes: Norfolk Hawker is not tolerant of brackish or saline water and overtopping of river systems can lead to localised extinctions. There are likely to be serious implications for the conservation of this species as a result of climate change and increasing sea levels. Without sufficient coastal protection and inland defences, the predicted sea level rise is liable to inundate the Broads with salt water, forming an estuarine ecosystem. If this is allowed to happen, Norfolk Hawker populations will be decimated, because sea water kills both the dragonfly larvae and Water Soldier plants.
  • Conversion of grazing marsh to arable farming: During the last century, substantial areas of grazing marsh were lost through conversion to arable land. This significantly reduced the amount of suitable breeding habitat for Norfolk Hawker. Similar changes in farming practice in the future could further threaten the remaining grazing marshes and their dyke systems.
  • Inappropriate ditch management: Unsympathetic management or neglect of the ditch and dyke systems are severe threats to Norfolk Hawker. The consequences of the loss of traditional benign dyke management techniques are uncertain, as little scientific study has been undertaken, but it is believed the effects are detrimental. Dredging of dykes with machinery increases suspended sediment and removes dragonfly larvae as well as plant material. Additionally, pumped drainage systems cause fluctuations in water levels; these and in particular lowered water tables, disrupt suitable habitats.
  • Eutrophication: During the last century, excessive nutrient enrichment of the rivers and broads has occurred as a result of the intensification of agriculture and a rising human population. Changes in agricultural practice and increasing pollution from both domestic and agricultural sources have led to a rapid increase in the levels of nitrates and phosphates entering the aquatic system. This in turn has led to a loss of aquatic vegetation and an increased incidence of algal blooms, despite improvements in sewage treatment.
  • Toxic inputs: The following causes of toxicity have contributed to a general decline in aquatic environments: runoff from agriculture (particularly pesticides), industry, the transport network and domestic sources.

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Current Action in Norfolk

  • Some suitable management work for Norfolk Hawker has already been carried out by Norfolk Wildlife Trust and Natural England on sites in Norfolk. Scrub clearance to re-establish fen habitat, dyke creation and regular traditional dyke management have all been shown to benefit this species.
  • Studies on the biology of this species are being carried out, or have been supervised, by members of the British Dragonfly Society.
  • Most of the main breeding sites for this species are designated National Nature Reserves (NNR), Sites of Special Scientific Interest (SSSI) or Special Areas of Conservation (SAC).

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Action Plan Objectives and Targets

National

  • Maintain the current (2009) UK range by preventing loss of freshwater sites in Norfolk and Suffolk.
  • Ensure all populations are in Favourable Condition (as defined by the statutory agencies) and increase populations within the current UK range by improving site management and creating new habitat.
  • Increase the current UK range by up to three locations by 2020 using re-establishment at former sites and/or by 'conservation introductions'.

Norfolk

  • Maintain the current (2009) range in Norfolk by preventing loss of freshwater sites.
  • Increase populations within the current Norfolk range by improving site management and creating new habitat.
  • Increase the range in Norfolk by one site by 2020, if proven to be feasible.

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