Review and rejuvenate

The work diary is filled with Annual Reviews at the moment; a yearly assessment of how each nature reserve is performing against its habitat and species targets.  Two of the top 12 wetland reserves in the UK for waterbirds were recently visited for a review: Berney Marshes/Breydon Water and the Ouse Washes.

Rejuvenation of key areas of habitat by a careful bit of ‘disturbance’ turned out to be a dominant theme for both sites.  Nature reserves can become rather ‘tired’ over a number of years as habitats become rather stable under routine management operations and the actions of natural succession.  Early succession wetland habitats in particular can become overgrown as invasive swamp species begin to dominate what were previously bare muddy areas with annual plants.  In many habitats, a degree of disturbance can knock back the succession and open up opportunities for a greater variety of species to flourish again.  This disturbance through management is seeking to mimic natural events such as flood and drought.  

Berney Marshes recorded a peak of over 91,000 waterbirds last winter and over 200 pairs of waders bred in the spring.  Increasing areas of rough grassland are being retained around the reserve; last year it also had up to 5 Rough-legged Buzzards and 16 Short-eared Owls.  However, the ditches and floods within the wet grasslands are the key feature of the reserve and increasing amounts of Sea Club-rush can become a problem in these areas as the grazing animals avoid eating it.  Staff at Berney have been drying out, cutting and rotovating areas of club-rush with great success, allowing re-colonisation of the resultant muddy ground on re-flooding by annual plants that provide abundant food for wildfowl. The newly flooded pools were covered with hundreds of Lapwing, Wigeon and Teal.  New projects currently being planned on the reserve will deliver significantly more scrape and lagoon habitat alongside Breydon Water for the benefit of terns, Avocets and passage waders.

The Ouse Washes has been suffering for a number of years from increasingly frequent summer flooding, resulting in a sharp decline in breeding waders as nests are washed out.  As a result, conservation work in recent years has been directed at creating habitat outside of the washes.  This year, the so called ‘Pilot Project’ the initial trial of creating wet grassland habitat for breeding waders on ex-farmland adjacent to the washes, held an amazing 174 pairs of waders on 76 ha.  The dry summer this year also allowed some increase in the waders on the main washes. The ‘crake-ometer’ accurately reflected the dry summer conditions: Corncrakes increased to 3 or 4 while the wet-loving Spotted Crakes were absent.  The fenland Cranes are increasingly finding the washes to their liking with up to 21 present at the moment.  Scrapes and floods grow over quickly on the Washes so the dry conditions have allowed a considerable amount of restorative habitat work to be undertaken.  New scrapes have been created and chisel ploughing has opened up compacted soils to the delight of feeding Snipe.  This work will significantly benefit waders and waterfowl in the coming breeding season – if the rains stay away.

Photos: above Wigeon and Club-rush rotovation at Berney. Below: wildfowl and new scrapes at the Ouse Washes.

Lac de Grand-lieu

The Lac de Grand-lieu has been the origin of many of the colour-ringed Great White Egrets seen in the UK; a power-house for herons and another launching pad for UK colonisation.  A day on a boat with the warden Sebastien Reeber brought home what an amazing wetland this is.   The Lac de Grand-lieu has open water (the lake), reed, marsh extensive willow scrub, wet woodland and surrounding wet grassland.   The water is around 0.8-1.5 m deep in summer but rises by 2 m in winter to cover an amazing 6,000 ha. The levels fluctuate annually to maintain a huge dynamic wetland.

The summer extent of the lake is around 2,000 ha and of this 1,000 ha is covered in water lilies.  It took half an hour or so to pass through the lily zone, mobbed all the time by Whiskered Terns.  Sebastien listed the breeding birds: 2,000 pairs of Whiskered Tern, 1,000 pairs of Cattle Egret, 160 pairs of Spoonbill, 300 pairs of Little Egret, 160 pairs of Purple Heron, 250 pairs of Night Herons, 700 pairs of Grey Heron…….  In winter, there are 13,000 Shoveler, 5,000 Pochard...  The Great White Egrets have been established as a breeding bird since 1994 and have increased to a current total of 160 pairs over the last 20 years.

The wet grassland beyond the lake will typically be submerged by 1m or more of water during the winter before the levels drop in April/May.  The breeding birds include Black Tern, Black-necked Grebe and occasional Ruff amongst the more familiar waders.  The ‘yellow’ wagtails on site are an intergrade between flava and iberiae with a corresponding range of head patterns.  An endangered plant now restricted to just a handful of sites in the UK, Starfruit was abundant along the tracks, along with Lesser Water-plantain.

The wetland is however, far from being in a ‘natural’ state.  Invasive non-native species are a major problem, with some of the most obvious being Red Swamp Crayfish, Sacred Ibis, Black Swan, Coypu and Muskrat.  We don’t want any of these in the UK!   And yes, there are plenty of Ruddy Ducks.  The Sacred Ibis are being controlled.  Formerly 800 pairs, they are now reduced to around 300.  The Ibis are a major predator of the eggs of birds on the wet grassland but perhaps more of this later.

Red Swamp Crayfish is now abundant in the wetland – abundant to the tune of 2 tonnes of crayfish per hectare. Perhaps their most obvious effect is the devastating loss of submerged aquatic weeds.  RSC have previously spread throughout the Camargue, where they have been well studied since they were first found in the 1990s.  The RSC have a varied diet (insects, fish, amphibians, plants and seeds) essentially made up (80%) of organic matter and detritus.  Introduction of crayfish into ponds showed that after 10 weeks a density of 3 RSC m² leads to an 80% decrease in the biomass of macrophytes and a 33% decrease in the diversity of macro-invertebrates.  On the plus side, they now form the major prey item for some wetland birds; 67% of the diet of Bitterns and up to 80% of the diet of Glossy Ibis, Spoonbill and Cattle Egret.  The Red Swamp Crayfish create a direct link in the food web between organic detritus and the top predators, providing the latter with a large invertebrate prey (primary consumer) in high numbers, increasing the overall amount of food available to them.   Even I can’t eat enough crayfish to get us out of this mess.

Above - lilies, Whiskered Tern, and nest.  Below: not-so-sacred Ibis, Starfruit, Flava/iberiae wag.

Magnam swirls take shape.

Heard of Bowers Marsh yet? No? Believe me, if you are a birder, you will do before long. I was back down in south Essex yesterday to look at the continuing development of this new RSPB nature reserve. This massive habitat re-creation project aims to create a range of dynamic, salty to fresh, wet to dry, Thames-side habitats. I have previously blogged about Bowers at an earlier stage of the work. Now the diggers have done most of their work and some areas have started to ‘settle down’. Compare the top picture here with the same view below. Avocets have already moved in and bred on the new ‘creek’.

The new 20 hectare scrape will also function as a reservoir for the grazing marsh habitats; brim full in winter but releasing water through the spring and summer to keep the marsh wet. Today the contactors carefully placed a ‘topping’ of sand and gravel on the islands constructed within the scrape, but how do you explain to dozer drivers how you want the mix spread? Well, I pondered, bit the top off my ice cream (it was a warm day), looked down, and said “We need to create intimate swirls of differing substrates, from sand to chocolate, sorry, I mean gravel”. And so the Magnam swirl island was conceived.

This week, the first tides surged onto the new saline lagoon. The lagoon will eventually support a mix of mud flats, saltmarsh and islands. Tides will flow on daily to controlled levels. Gulls seem to like the new habitat; Meds and Yellow-legs mingled amongst the hundreds of Herring and Lesser Black-backs.

Thinking and tinkering

One particularly energetic discussion with Dutch colleagues on the recent trip to The Netherlands centred around the qualities that make a good reserve manager. Why do some reserves appear vibrant and others as dull as ditchwater?

‘Thinking and tinkering’ is a phrase that may well sum up the best of reserve wardens . The great old wardens of yore ( and the best of today), were forever tinkering with their reserves; thinking about how to change things for the better and trying things out. Good reserve management requires an intimate knowledge of the site and an inquisitive mind. Reading through some of the books by wardens, such as Bert Axell’s ‘Minsmere: Portrait of a Bird Reserve’, this is clear. The now famous ‘scrape’ appeared bit by bit over at least 12 years. Trial and error was involved in getting it right, and much tinkering management by wardens and many volunteers.

Is this art of tinkering being lost? Perhaps. Nowadays, many wardens seem less connected with their reserves as the demands on their time increase and more time is spent behind the desk. Some even mutter about getting people in to monitor birds as they don’t have enough time!!   So how do we encourage the tinkerer? Well, partly it’s about appointing, and then developing, the right people in the first place, people with a passion for wildlife. However it’s done, we need more thinkers and tinkerers please.

What the Heck?

 

A bull Heck Cattle, Great White Egret and a forest of Red Deer stags - it is summer, the bushes are dead.

Oostvaardersplassen in The Netherlands is often held up as a fine example of large, natural dynamics management; but is it all it's cracked up to be?

A few days in The Netherlands exchanging views with Dutch counterparts was a chance to recharge ecological batteries and become inspired again. Speaking with Dutch ecologists the air was thick with bird talk, of detailed bird ecology. Of Purple Herons, Spoonbills, Baillons Crakes, White-tailed Eagles, Eagle Owls and more. Fantastic. The key topics of discussion centred around the strategic management of freshwater and coastal habitats, with an emphasis on potential colonists for the UK.

So, back to the Oostvaardersplassen. The Dutch Ecological Networks Plan aims to create 160,000 ha of ecological networks throughout The Netherlands. The Oostvaardersplassen is part of this network and extends to 60 sq km. The aim is to have a ‘natural’ system controlled by grazing and fluctuating water levels. The wetlands (around half the area) support large numbers of key species, including the largest colony of Great White Egrets in The Netherlands. The drier, peripheral land is grazed by huge herds of Koniks, Red Deer and Heck cattle. We saw several hundred of the 1,000 or so Koniks in one herd. It is hard to come to any other conclusion than that these areas are over-grazed; there is remarkably little diversity other than large herbivores, Greylag Geese, Red Foxes and Ravens. There is so little food in these areas that Marsh Harriers have to forage up to 8 km from the nest to find adequate food.

However, for wetlands, there are some key messages to be taken from here: firstly, big is critical for colonising populations, and secondly, dynamic water management is essential to maintain populations of wet reed species. We need to take this on board in the UK.

We saw White-tailed Eagles with newly fledged young, the colony of Great White Egrets, Savi’s Warblers, Bluethroats, Bearded Tits, Spoonbills, White Storks, Montagu’s Harrier and Goshawk, but more of these later...

White-tailed Eagle and nest (nice turbines!), Koniks, view over the Oostvaardersplassen.