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.

Rejuvenation

 

Reedbeds under conservation management have traditionally been managed by rotational cutting, with the objective of slowing natural succession. Even on a small site, such an objective is questionable, but with a site of over 200 ha, this is not a feasible option. So Ham Wall in Somerset is the focus of a larger scale ‘reedbed rejuvenation’ project, a trial of a new form of reedbed management.  Compartments of up to 20 ha will be held at a lower water level for a number of years and reverted to grassland by a combination of cutting, burning and grazing. After maybe five years, the ground will be re-flooded to create shallow open water and reeds will slowly re-colonise.  Compartments will be 'rejuvenated' on rotation in order to maintain a range of successional states within the reedbed.

I returned to Ham Wall last week to look at the first compartment to be managed in this way and recently re-flooded after several years of drier conditions.  So what will happen next?  Well, we expect the newly flooded habitat will provide good feeding opportunities for a range of reedbed and wetland birds as the reeds regain dominance over a number of years.  In the short-term, it should attract large numbers of waders, wildfowl, egrets and herons over the next year or so as water levels fluctuate, particularly as they drop in late summer.  The land will be allowed to revert to reedbed, with higher water levels, and continue through its succession to old, littered reedbed, before the process is repeated.

Although early days, the first signs are promising.  Large numbers of duck, including Teal, Wigeon, Gadwall and Shoveler are already using the area, with Lapwing and up to 200 Snipe around the margins.  A dozen Water Pipits flitted around the margins.  A couple of Great White Egrets were in the area and it is hoped they will find the area to their liking.

In the beginning.......there were LRP's

 As December ticks away, I eventually get to the task of sorting out the years records from the notebook.  If only I was a little more organised.  This week’s task was to complete the analysis of one of my regular breeding bird surveys; at Amwell Quarry (now nature reserve).  The run of data on breeding birds for this site now extends back to the late 1970s when mineral extraction began.  Why have I done this for 35 years?  Who knows, it just happened.

Eighty species have bred at Amwell over those years, 46 of them managing to enter the ‘scoresheet’ for 2012.  This is somewhat below the 53 species in the best year; 2001.  These 46 species amounted to a total of 327 pairs of birds, again somewhat below the peak of 410 pairs in 2002.  So the headline story is somewhat of a rise and fall.  However, as you would expect, these figures hide the many changes over the years.  A number of species, such as Willow Warbler, Yellow Wagtail (5 pairs in 1983), Turtle Dove, Linnet and Tree Sparrow, have all declined more or less in line with national trends.  But without doubt, the major influence has been successional changes in the habitats, with meadow, marsh and mud being replaced by reed and willows. 

These changes have, of course, produced a number of winners: Grey Herons and Cormorants in the trees, recently joined by Little Egrets, and Reed Warblers, Cetti’s Warblers and Blackcaps in the reed and scrub.  In addition, Black-headed Gulls and Common Terns have used the rafts provided.  The losers have been the grassland birds of the old meadows and more significantly the variety of wildfowl and waders.  Tufted Ducks peaked at a massive 62 broods in 1987 but have since dropped away to low single figures.  Likewise, Gadwall rose to a peak of 12 broods before dropping to just one and after peaking at 53 pairs, Sedge Warblers have dwindled to just 14 as habitats have changed.

Wading birds, particularly the Little Ringed Plover, have always been a key feature of the site since the mineral extraction began.  LRPs peaked at 8 pairs but with numbers rising and falling in relation to the amount of habitat.  Despite the recent addition of Oystercatcher in recent years, LRPs and waders in general, are now teetering on the edge of disappearing as breeding birds.   The problem is that the relentless march of reed and other vegetation across the formerly open areas outpaces the management effort.  What is needed, what most old gravel pits need, is a bit of Localised Intermittent Catastrophe.  A combination of controlled vandalism with a large digger and some dynamic water management should help knock selected areas back to an earlier stage in the succession so the process can start again.  We gathered on site this autumn, umm-ed and arr-ed a bit, and some good work was subsequently undertaken, but on reflection, much more of the same will be required if LRPs are to remain until the end.

Below - Amwell 1987 (8 prs of LRP), Amwell 2012 (none).

 

KP (3); the rejuvenation

Freezing fog and five Great White Egrets greeted us at Ham Wall as we met to review last year’s management. Overall a very satisfactory year with 8 Bittern nests, successful breeding of Little Bittern, attempted breeding by Great White Egret and a singing Savi's Warbler.

Reedbeds under conservation management have traditionally been managed by rotational cutting, with the objective of slowing natural succession. Even on a small site, such an objective is questionable, but with a site of over 200 ha, this is not a feasible option. So Ham Wall is the focus of a larger scale ‘reedbed rejuvenation’ project. Compartments of up to 20 ha will be 'perturbed' by holding at a lower water level for a number of years and reverted to grassland by a combination of cutting, burning and grazing. After maybe five years, the ground will be re-flooded to create a shallow wetland. Reeds will slowly re-colonise but the return to early successional habitat will attract large numbers of waders and waterfowl in the early years. The land will then be allowed to return to reedbed, with higher water levels, and continue through its succession. Compartments will be 'rejuvenated' on rotation in order to maintain the early stages of reedbed.

The wet, early successional reedbed will benefit Great White Egret (as well as a range of other species) and we hope breeding will become established. The Dutch population at the main breeding location in Oostvaardersplassen reached a record high of 154 pairs in 2010 after the creation of additional feeding habitat in the late 1990s. Similar habitat will be created at Ham Wall.

KP (2)

Radipole Lake has been punching below it's weight for many years. With the second phase of the restoration programme completed this winter, it is beginning to look fighting fit at last. The key issue has been one of habitat stability and a resultant lack of diversity, now being ably tackled by the current reserve staff, with a bit of Kick-ass Perturbation.

With restored ditches and new pools in place (see above), attention can be turned to reed management. Some of it should be simply got rid of; grazed out and replaced with swampy grassland (some of it suitable for passage Aquatic Warblers). Some short-rotation and some long-rotation cutting is required, and commercial reedcutting is not a bad option for the former. Often considered an anathema by conservationists, it all depends on scale, and small-scale regular reedcutting is undoubtedly good for Bearded Tits. BTs benefit from mosaics of different aged reed; cut reed, young reed, old reed, extensive edges next to water, pools, shallow scrapes and ditches. There are good examples of reedbeds where declining management has resulted in declining BT populations, and conversely examples where re-invigorated management has been matched by a resurgent BT population (look no further than Blacktoft Sands).

Commercially cut reed blocks will result in fixed reed clearings for a number of years but in the right size and location can provide good habitat for BTs as well as an assortment of other birds from Water Pipits through Snipe and duck to Cranes. A Dutch study found that you can remove up to 50% of the standing crop of a reedbed annually with no loss of breeding birds. On nature reserves, a maximum removal of 20% would be more appropriate.

Cut reed blocks and ditch management should increase interest for visitors as more birds become visible. Overall, continued 'disturbance' in the habitat should maintain it's diversity of wildlife.  Not much was visible today however - a Marsh Harrier, a few Bearded Tits and a Goosander, the 6+ Bitterns present managed to avoid being seen.

Kick-ass Perturbation

Radipole Lake, Little Egret.

Too many of our wetland nature reserves have become ‘tired-looking’ and ‘stale’ over the years. Ongoing same-old, same-old management has allowed stability in the habitats, usually with competitive species becoming dominant. In many habitats, a degree of disturbance can knock back the natural succession and open up opportunities for a greater variety of species to flourish again. This management disturbance may mimic natural ‘catastrophes’ such as wind, flood, ice or fire, which, in the longer term, are rarely as bad as they first seem. Such ‘Kick-ass Perturbation’ (as a colleague nicely puts it) can be highly beneficial as the habitat vigorously recovers. A good example is the recovery of the Strumpshaw fish population here.

Why don’t we do more of this KP? Well, lack of resources, perhaps a fear of change, and of complaints from visitors (incl. birders) who see the changes as damaging, are some of the reasons. The first time I instructed a large excavator to re-dig an old ditch on a SSSI, I couldn’t sleep for days I was so worried about what I had done. Within minutes the black scar was extending across the land and the ground shook as each bucketful of silt was lifted. One year later the site looked fantastic, ‘long-lost’ species had returned.

Anyway, getting to the point, and on to Radipole Lake, the latest stop on the reedbed tour. On a previous assessment back in 2006, I had identified the lack of lack of structure within the reedbeds and the lack of ditch maintenance as a key factor in the site’s decline. A plan was drawn up. That plan is now halfway through implementation and the initial results look excellent. Some great looking KP has been performed on the ditches and pools. The water now ‘boils’ with invertebrates and fish, and studies of the bats has shown increased use of these restored areas by feeding Daubenton’s and Noctules. Give it 2 years and I will expect booming Bitterns.
The major distraction during the visit was the number of Great Green Bush-crickets chirping away. Lodmoor looked good, with 3 Curlew Sandpiper, 2 Spot Reds, Ruff, Redstart, Wheatear and several Med Gulls.

Below - aerial views of Radipole before and after restoration of the ditch systems.