Fancy a bit of rough?

Field Vole, SEO pellet, Bank (left) and Field Vole skulls, showing the diagnostic extra loop on the upper middle molar of the Field Vole.

This winter’s influx of Short-eared Owls, Hen Harriers and Rough-legged Buzzards has been one of the highlights of the season. Many have settled in areas of un-grazed, rough grassland, a habitat that often seems to be quickly dismissed by conservationists as having little value. It is often botanically poor (especially if it’s of recent origin) and the list of ‘what to do with it?’ usually starts with grazing or mowing.  Rough grasslands can support good populations of small mammals, such as voles, a major part of the diet of these species. Voles and some other small mammals typically show cyclical patterns of abundance. After a crash in the small mammal populations in the northern breeding areas of these birds, they move south and west and settle to winter where suitable food is available.

The diet of Short-eared Owls has been shown to consist of 95% of small mammals over numerous studies. In Britain, Field Voles account for about 85% of the diet. When voles are scarce however, SEOs will take an increased proportion of birds. In the early 1980s when SEOs regularly wintered in the Lee Valley, remains of birds were numerous in the pellets, forming a third or more of prey items. The owls seemed to be specialising on thrushes, Skylarks, finches and buntings. A pellet from one newly arrived owl at Nazeing contained the leg of a Blackbird that had been ringed previously on the Essex coast. Half a dozen pellets picked up from Heartwood Forest this weekend revealed remains of 9 Field Voles and a single Bank Vole. Rough-legged Buzzards also specialise in small mammals, notably voles and lemmings, although wintering UK birds are noted as favouring Rabbits.

Field Voles favour rough grassland with a dense thatch in which to burrow. In new grasslands they reach reasonable densities by the second year of establishment. Some research has shown that SEO hunting periods over rough grassland are positively related to vole densities until the grassland becomes densely thatched. At this stage (greater than 80% dense thatch), the relationship switches to negative; there are just as many, if not more voles, but the density of the vegetation makes them less vulnerable to predation by the owls. However, there is some suggestion that light grazing or limited cutting of older grassland may benefit the voles in that it promotes more vigorous growth of fresh, palatable grass. Such practices are just as likely to benefit the owls. So rotational strip mowing in old, tussocky grassland (perhaps a 4-6 year rotation) may benefit voles by producing fresh growth and owls by making the voles more available.

Below - Rough-legged Buzzard

Hard work

A couple of days working down in the south-west looking at ongoing projects was a bit of a strain. At Radipole Lake, the reedbed is in the best condition it’s been in for years after a considerable amount of restoration work. The chance of a booming Bittern this coming spring is as high as it has ever been. It would have been rude of course not to pop in to the visitor centre, where a quick check through the assembled mass of 300+ Med Gulls revealed 2 Ring-billed Gulls. Onward then to Exeter for an afternoon meeting at Goosemoor, a small area of land next to Bowling Green Marsh at Topsham and the site of the first Regulated Tidal Exchange in the UK. Regulated Tidal Exchange is a technique for creating and managing intertidal habitats. It uses regulated quantities of tidal water to manage the inundation regime and is often employed behind maintained sea defences. The technique has been particularly well developed in the eastern USA where impounded coastal wetlands, often in close proximity to built development, have benefited from the re-introduction of tidal flushing. The project at Goosemoor, implemented in 2004, has created a range of saline and brackish habitats (0.75 ha saline lagoon, 0.75 ha of mudflat and 4.25 ha of saltmarsh) for the benefit of breeding and wintering waterbirds. It would have been rude not to pop in to Bowling Green Marsh, just in time for the Red-breasted Goose to fly over our heads and land in front of us. At nearby Exminster Marshes, we looked at the successful use of wild bird cover crops (more of this at a later date), and were forced to endure some extremely close views of the long-staying Glossy Ibis as it wandered around us.

The following dawn saw us on Ham Wall, Somerset as a rough half-million Starlings left their roost and cruised over in one sky-wide, minute-long, wing-whirring flock. Two Great White Egrets joined a feeding frenzy of 20+ Little Egrets, half a dozen Grey Herons and a Bittern. Five Bewick’s Swans bugled nearby and an Otter spooked a flock of Tufted Duck. A quick crash around the reedbed to look at the conversion of reed into compost and briquettes was briefly interrupted by a flyover Water Pipit. And finally a quick look at the Somerset Levels was enlivened by the bunch of re-introduced Cranes with their hang-along wild mate (right-hand end, below). Work is a real chore.

Photo by John Crispin

Red sauce, Brown sauce, Bean Geese

Top - Taiga Beans and others.  Middle - Wigeon making the habitat unsuitable for Taiga's. Bottom - Pinks (at least they were close).

Northern people are supposed to prefer brown sauce while southerners go for the red stuff. Not for the first time, I pondered this piece of mythology the other day whilst waiting for the Taiga Bean Geese to become rather more than distant dots on the far side of Buckenham Marshes and for their little mate, the Lesser White-fronted Goose to appear. What prompted this deep, re-sauceful thinking you may ask? Well the Taiga’s are feeding predominantly on Buckenham rather than Cantley this winter.

Only two locations regularly support populations of wintering Taiga Bean Geese in the UK: Buckenham and Cantley Marshes in the Yare Valley, Norfolk, and the Slamannen Plateau in Scotland. Ringing results have suggested that the two populations breed in different parts of Scandinavia. The majority of the individuals visiting central Scotland probably belong to a fully wild sub-population, which is distinct from the one wintering in Norfolk. Part of the central Scotland flock may also derive from a re-introduction project, which started in 1974 in central Sweden. The Scottish birds tend to arrive in October. By contrast, the Norfolk birds appear to leave their breeding area in Sweden for a wintering/staging area in Denmark, before a proportion move on to the Yare Valley around the end of the year.

Now to the brown sauce, red sauce conundrum. Taiga Bean Geese have been using Buckenham and Cantley Marshes since the 1930s with numbers peaking at 1,000 birds in the 1936-37 winter. Research has indicated that the Yare Valley Taiga’s prefer to graze on unimproved pasture, feeding particularly on meadow-grasses (Poa spp). It is suggested that the large body size of the Taiga (and their disproportionately large guts) allows a more effective digestion of taller, poorer quality food than their smaller-bodied competitors. A shift from preferring Buckenham to Cantley during the 1970s was associated with a shorter sward on Buckenham resulting from increased grazing by Wigeon and sheep. As a result a proportion of the fields at Cantley are maintained to this day at a longer autumn sward height especially for the Taiga’s. By contrast, research on the Slamannen birds has shown that they feed on ‘improved’ grass fields and particularly on Rye Grass (which is apparently less digestible for the Yare Taiga’s). So how comes two populations of birds of the same species, breeding in the same country, can be so different in their digestive traits?

Hmmm confusing. Now, there is a clue to all this in the name – ‘bean’. So called, because on the continent they traditionally feed on arable farmland in the autumn, firstly on stubbles, then on waste root crops, with a shift to cereals and grasses late in the winter. Perhaps at the end of the day the research should be seen as just a ‘snapshot’ of what is happening. Grass-feeding waterfowl will specialise on the most energetically efficient area of food determined by their body characteristics. And a number of factors will also affect where the birds choose to feed, not least disturbance, to which Taiga’s are apparently sensitive. The Bean Geese will choose to feed on what is most nutritious and available in their traditional wintering areas given the conditions that prevail. But quite clearly you can’t have brown sauce on a burger ....and red sauce on bacon is a complete no-no wherever you come from. Arrh, there’s the Lesser White-front.

Lee Valley doldrums

A total of 90 species seen throughout the valley in a thrash from bottom to top failed to disguise the dullness of the current situation. Highlights? Not really, just 2 drake Smew, 3 scattered Red-crested Pochards and a Med Gull. Wildfowl numbers are generally very low, with the exception of Gadwall. This winter has produced some high numbers, with the November peak of 500+ on Holyfield now dispersing to other sites. A couple of Ruddy Duck survive. About 30 Goosander are around, mainly in the favoured Turnford Marsh/Holyfield/Nazeing zone.

Just 3 or 4 Bittern are wintering at 3 sites (but I failed to find any of them). By contrast 30+ Little Egrets are arriving at the 2 roosts at either end of the valley. No Jack Snipe seen today, but these days all the places they are likely to be found are out of bounds.

On the passerine front, winter thrushes were the most numerous birds today, with 500+ each of Redwings and Fieldfares. They seemed to be everywhere. There also seems to have been a recent arrival of Chiffchaffs. I saw three today but up to ten may be at Rye Meads; 7 were ringed yesterday. But where are the finches? Linnet was a noticeable miss today but there seems to be no weedy areas left.

Holyfield/Cheshunt area: 2 drake Red-crested Pochard, drake Pintail, Little Owl, 500+ Redwing.

Girling: 18 Black-necked Grebes, adult Med Gull, 13 Goosander.

Walthamstow Res: 6 Ring-necked Parakeets, 4 Shelduck.

Rye Meads: 3 Chiffchaff, Cetti’s Warbler, 2 Shelduck.

Amwell: drake Smew, Red-crested Pochard, Yellow-legged Gull, 2 Lesser Redpoll.

Wallasea

Top two - Wallasea present.  Lower two - Wallasea future? (Tiengemeten)

A trip out to Wallasea Island in Essex this week reminded me of a visit to The Netherlands earlier this year. The Wallasea Island ‘Wild Coast project’ is a landmark conservation and engineering scheme for the 21st century, on a scale never before attempted in the UK. The aim of this project is to combat the threats from climate change and coastal flooding by recreating the ancient wetland landscape of mudflats and saltmarsh, lagoons and pasture. It will also help to compensate for the loss of such tidal habitats elsewhere in England.

Although the Wallasea project may be the largest of its kind in this country, the Dutch are ahead of us in this sort of restoration. In the summer, I visited the island of Tiengemeten in South Holland and had a glimpse of what Wallasea may come to look like in the future.  The project at Tiengemeten was undertaken as part of a programme to restore 3,000 ha of tidal areas in the Dutch Delta region, itself part of the wider Dutch Ecological Networks Plan to create 160,000 ha of ecological networks. Tiengemeten extends to 1,000 ha and was formed as agricultural land claimed from saltmarsh. Now it is being returned to near-naturally functioning habitat. The island has been divided into three zones. The Wilderness zone covers 700 ha and is ex-arable land now open to the influence of the tides and water regimes of the island. The Richness zone (250 ha) is a landformed area of shallow flooding, reedbed and scrub, wet in winter, drier in summer. Finally, the Cultural zone (50 ha) is made up of a campsite, a cafe and a few houses and cropped fields. Grazing by Highland cattle is the primary management tool.

The island was officially given back to nature in 2007 after it was purchased by the Dutch Government. In 2008, a full breeding bird survey was undertaken. The results included the following totals (pairs): 87 Bluethroat, 125 Avocets, 4 Black-winged Stilts, 151 Marsh Warblers, 18 Black-tailed Godwits, 11 Garganey, 3 Spotted Crakes, 3 Goshawk, 1 Corncrake and 612 Greylag Geese. Another full survey was undertaken this year and the results are awaited with interest.

Meanwhile, back on Wallasea, the landscape is still of arable fields surrounded by sea walls, and it has a way to go to match Tiengemeten. Despite this, the birding provided some anticipation. Thousands of Brent Geese and Lapwings fed in the fields. Hen Harrier, Marsh Harrier, Merlin and Peregrine hunted around the sea walls or over the areas of un-harvested crops retained to provide food for farmland birds. A single Rough-legged Buzzard and a Spoonbill provided the highlights for the day.

Fishy pits

Pike and crayfish sushi appears to be on the Christmas menu of the Great Northern Diver currently residing at Nazeing gravel pits in the Lee Valley.  A largish crayfish brought up from the depths was dispatched with some skill.   Nazeing is not the most exciting of the valley waters for the birder but being one of the largest of the gravel pits, it does occasionally specialise in stray seabirds.   Black-throated and Red-throated Divers have made long-staying appearances, as well as visits by Velvet Scoter, Long-tailed Duck and Fulmar.  In the dim and distant, a Little Bittern was also seen, not that there’s much habitat for it today.  Prior to the 1970s, Nazeing held huge numbers of diving duck, mainly Tufted Duck and Pochard.  Numbers declined sharply and remained low until recent years when numbers have increased again, probably due to reduced disturbance as the amount of sailing has declined. 

The lack of aquatic vegetation, either submerged or marginal, results in minimal numbers of herbivorous wildfowl, even Coots are remarkably sparse.  However, fish populations are good, as evidenced by the numbers of Great Crested Grebes (usually up to 50) and Goosander (20+ at peak).  Nazeing is currently one of the best sites for Goosander in the valley, with the last 15 years seeing a significant shift in Goosander distribution from the Lee Valley reservoirs to the gravel pits.  The size and openness of the lakes attract passage terns and gulls.  The northern lake intermittently supports a small gull roost; in the past with up to 10,000 birds nightly, mainly Black-headed and Common Gulls, with the occasional Med Gull.  When spring tern passage is underway, a quick check is often productive.  If Arctics or Blacks are about, there a fair chance Nazeing will pull one.

An Eastern Crowned Warbler once flew halfway across this ride

....and into a whole net of controversy. And who’s fault was it that we didn’t see this eastern gem – well it was everyone’s apparently, although no-one seemed to blame the warbler for flying off. It was apparently released into a willow tree, with barely a good-bye, but at that time it was just a Yellow-browed Warbler, low-life amongst asian vagrants, barely worth the time of thinking ‘not a bad inland record’ let alone travelling to try to see it. Then its true colours were revealed (good job they didn’t have to send the prints off to Kodak) and the greyness of its crown matched the blood-drained faces of the local birders who suddenly realised Hertfordshire’s one-in-20-year-good-bird was at Hilfield Park Reservoir, otherwise known as 'Fortresss Hilfield'.

There was some talk that some didn’t want the news to be released. Now if ringers or birders don’t want to release news of a bird, that’s their decision as far as I’m concerned. One might argue it’s a little anti-social as there can hardly be any birder who hasn’t at some time gone to see a bird found by someone else...but it is their decision and should be respected. I’ve nothing against ringers either, quite the contrary. Did you know that, statistically speaking, 50% of the UK’s recorded Eastern Crowned Warblers have been picked out of a net. However, this was Hilfield Park Reservoir – a designated Local Nature Reserve (LNR), and according to Natural England “LNR’s are for both people and wildlife”.

The trouble is, I’m not sure how many ‘people’ are thought should benefit from an LNR, but it surely must be more than the present number, and it would certainly include the hastily formed Hertfordshire branch of the Eastern Crowned Warbler Appreciation Society (ECWAS). Okay, so the birds of the site are well recorded and documented in an excellent report (where you can see that the site doesn’t actually have many ‘crowning’ moments). There is a view that withholding bird news is in the best interest of the conservation of the site. But ultimately is it really beneficial for the future of the site?

Back in the early 1990s, the Wildlife Trust stoutly defended this site against a planning application to locate the nearby sailing club on the reservoir. Had it lost, the site would not support its current importance for wildlife. One of the main arguments used at the time was that the site was not fulfilling its LNR objective – ‘for both wildlife and people’, as few people were allowed in. Now this is a water company operational site and understandably there are rules to be followed. Anyone can access this site if they are a Wildlife Trust member and arrange to pick up a key (as it has always been). But opening the site for special events requires a bit more organisation and supervision. And by the time the ECWAS arrived, it was apparent that the warbler’s discoverers had scarpered as quick as the bird itself. Perhaps if the spirit in which the site was designated is to be fully realised, a ‘friends of...’ group, with a specific remit to both record wildlife and ‘encourage use of the site’, might be a better bet for the future.