Tipping the balance

There often seems to be an assumption that if birds are going to colonise the UK, then it will just happen.  However, successful colonisation is by no means inevitable and some species may need a lot of help to do so.  In addition, these newcomers often seem to be valued less than declining ‘outgoing’ species, but why should colonising species be less important than those declining?  If their range is shifting in our direction as a result of deteriorating conditions elsewhere, their conservation needs may be just as important.

Black-winged Stilts are a good example of a species ‘heading our way’.  There has been an increase in breeding attempts by stilts in the UK in recent years. Unfortunately, Black-winged Stilt productivity in the UK has been poor.  There have been 13 nesting attempts since 2005, six have hatched young, and these 13 nesting attempts have fledged just seven young (all last year).  So, this amounts to an overall productivity of just 0.54 young per pair.  By contrast, it was a pretty productive breeding season for stilts in the Netherlands last year, and the ten nesting pairs there fledged 26 young (2.6 young per pair).

This year, 2 pairs of Black-winged Stilts attempted to nest at Cliffe (photos below).  They failed to rear any young, despite a considerable amount of effort, including a predator control plan and a 24-hour watch.  The young chicks were unfortunately predated by Black-headed Gulls within a few days of hatching.  This has however, provided much useful information about how to deal with future events.  The key is to act fast when birds arrive and put in place all the necessary protection.  However, a more forward thinking option is to attract the birds into safer nesting areas by improving the habitat.   In short, we need to tip the balance in their favour.  Such actions will also benefit other key species using the same habitat, such as Avocets and terns.

The Great White Egret is another species currently in the early stages of colonization of the UK.   There are interesting lessons to be learnt from the colonisation of The Netherlands.  Numbers remained low for some 25 years at the colonisation site, the Oostvaardersplassen.  The trigger for an increase in numbers was the creation of a range of shallow water feeding grounds within range of the breeding site in the late 1990s   These shallow, clear waters are of importance to the egrets for feeding especially in the first part of the breeding season.  Chick production increased steeply after the creation of these areas and breeding numbers dropped in years when they were dry.  However, these changes allowed GWE to increase from less than 5 pairs in the 1990s to 143 in 2006.

We have tried to apply the same thinking to GWE colonization of the UK.  Where are the likely breeding sites?  Is there suitable nesting and feeding habitat? If not, can we put it in place?  The quality and quantity of food available to the birds is critical to both initiating breeding and breeding success.  In the UK there is a lack of suitable feeding areas around many of the likely breeding sites but with some thought this could, and is, being addressed.

In Somerset, the initial breeding was triggered by the creation of large reedbeds and then appropriate feeding areas bringing the birds into nesting condition.  Two or three pairs have bred annually since.  This year the provision of a high quality feeding area has coincided with a jump to 6-9 pairs. On a visit to the site in June, one feeding area contained 78 Little Egrets, 13 GWE (and a further 5 flying around) and a couple of dozen Grey Heron. Later in the season, another area provided feeding for fledged juveniles (photo above).

So, species may want to colonise, but the conditions may not be ideal.  We should be looking for opportunities to tip the balance in their favour.  This is of course no more than a decent reserve warden should be doing – thoughtful management of habitat to get the best result.

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.

A tale of simple fisherfolk

Little Egrets have come a long way since I first twitched one at Walthamstow Reservoirs in 1972.   Locally, the first breeding of Little Egrets in the Lee Valley occurred in 2006 when a pair reared 4 young amongst the Grey Herons at Walthamstow Reservoirs.  The valley total for this year seems to be at least 26 pairs in three colonies, at Walthamstow, Amwell and Netherhall.  All are tucked rather unobtrusively into Grey Heron colonies but at least 20 broods have been seen to fledge.   Further afield, the UK breeding population is now getting close to 1,000 pairs at around 100 colonies.  One of the largest colonies is at Northward Hill in north Kent where numbers grew to a peak of 124 breeding pairs in 2009, equalling and then exceeding the numbers of Grey Heron, before dropping to 114 in 2010 and then 94 pairs in 2011 as a result of two successive cold winters.  So this mainly fish-eating bird is on the rise.

By contrast, breeding Cormorants peaked in the Lee Valley a few years back at a little under 400 pairs.  Since then total numbers have dropped despite an increase in the number of colonies.   This year the number of active nests in the Valley was around 250 and reflects a steady decline locally over recent years. 

Which brings us neatly to the recent call by angling groups to add Cormorant to the general licence, thus easing the restrictions on killing.  Now, I spent a lot of time ‘angling’, well electro-fishing to be accurate, and then I’m only the assistant, brought along to get wet and carry the boat.  In attempting to create new wetlands, much time is  and effort is spent enhancing the underwater ‘fish’ habitat.  Fish populations reaching a critical threshold is one of the trigger points for getting birds such as the Bittern to breed.   Many reserves support good fish populations and the key issue is habitat quality, notably underwater landform, structure and connectivity, the water quality and the diversity of aquatic vegetation.   Cormorants have never been implicated as a problem on reserves except in an isolated case where an isolated pool was over-stocked to try and create a specific feeding area for birds.  And there perhaps we hit the main issue.  Not only do angling clubs frequently stock way above natural densities but they often tend to have sites with poor habitat quality. Redundant gravel pits for example, which even if earmarked as an angling lake, have little or no attention paid to the underwater habitat in the restoration process.  So the recent outburst against Cormorants smells rather fishy.  Rather than a serious attempt to address the real problems this looks like another attempt to solve a perceived issue with a gun.   

Conservationists and anglers should be on the same side.  Wouldn’t it be great to develop partnerships on some sites where we both work to improve fish stocks through good habitat management?

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.

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.