Sunday, 26 June 2011

Black-head squeeze, terns sore?

Tern rafts - 1) posh with street lamps and added BHG's, 2) double-decker accommodation at Walthamstow.

In the Lee Valley and elsewhere, a remarkable colonisation by breeding Black-headed Gulls has taken place in recent years, the birds squeezing onto rafts put out for Common Terns. This year at least 63 pairs are nesting at four sites in the valley. With the totals for the previous three years being 23, 9 and 1, it is clear Black-heads are moving in. Rafts at Walthamstow Reservoirs and Amwell have been colonised this year, adding to existing colonies at Rye Meads and Cheshunt.

Although the number of terns nesting in the valley has remained roughly steady at 70-90 pairs (with at least 81 pairs this year), there have been changes at individual sites. This is most notable at Rye Meads, formerly the largest colony in the valley, where a rise to around 40 pairs of Black-heads has roughly coincided with a drop in tern numbers, down to 11 pairs this year.

This has prompted much concern. Will the terns be ousted as the gulls increase? Are the two trends even related? And why have the gulls colonised now, after the terns have enjoyed up to 40 years of successful raft nesting?

Interactions between Black-headed Gulls and terns are well known; they may compete for space, the gulls may directly predate tern eggs and small chicks, and the gulls are also known as kleptoparasites – stealing food as the terns bring it in for the chicks. However, despite this, the two species regularly nest together; the terns may gain added security from predators from being within the gull colony. Watching the valley colonies, there are clearly a lot of noisy goings-on and squabbles. Terns with fish are chased, but mainly get through. Overall, both species appear to be having a very productive year with plenty of chicks on the rafts and the first young terns taking to the air. In excess of 100 young Black-heads are on the rafts.

What can be done, if anything, and does it even need doing? Black-headed Gulls themselves are declining at a number of coastal sites where even larger gulls predate them.  The techniques employed so far have been to delay the positioning, or to cover, some rafts until just before the terns settle (as Black-heads nest earlier). However, where terns frequently like to nest en-masse, the gulls seem to like to spread out amongst the rafts. Another solution may be to simply provide extra rafts to accommodate both species.

At Cheshunt recently, I spotted another ecological difference between the species, although it may not be statistically significant. I watched the terns bringing in a succession of small fish for the chicks. The only gull I saw regularly coming in with food appeared to have......(I joke not).....chips!

Thursday, 23 June 2011

Where now for Orioles?

With just 2 males and a single female having returned to Lakenheath so far this year, how long can this remnant population persist? There has been a steady decline in numbers since the heydays of the 1980s when 20+ pairs were in the area. Last year breeding was not proven.

It is perhaps worth thinking about why Orioles are so attached to the plantations of hybrid black poplars in the fens. There are numerous varieties of the hybrid black poplar, but only those with early leafing and large leaves are favoured. One variety ‘robusta’ is frequently chosen. The diet of Orioles appears to be mainly large caterpillars and it is assumed the poplars provide plenty of food, perhaps not exploited by other species. However, elsewhere in Europe, Orioles use a variety of trees as well as poplars.  Areas of woodland with swampy glades or clearings are often favoured, and the proximity of water is frequent.  So, the structure and location of the tree may be important but it has also been suggested that Orioles return to breed in the type of tree in which they were hatched.

So why are they declining?  One key theory is that Orioles need to breed in loosely connected concentrated sub-populations that form nuclei from which birds can radiate outwards. The fragmentation and reduction of the fenland poplar plantations may have resulted in an unsustainably small population of Orioles.  In addition, although climate change predictions seem to benefit Orioles in south-east England, subtle changes may be affecting food supply.  Despite the predicted benefits, at the present time we are seeing declines in northern European countries including the Netherlands.  The fortunes of the fenland Orioles may be linked to those across the water.

So what if anything can be done? New poplar plantations have been established at Lakenheath and are close to being of suitable age for Orioles. But is this enough?  It may be that only the planting of a large 500 ha+ poplar woodland will solve the fragmentation problem. One slight conundrum is that hybrid poplar plantations are not a natural part of the countryside and are not used by a wide variety of species.  So, could we diversify the plantations into a more natural wet woodland community but ensure a proportion of the appropriate poplar variety, and maybe hope that Orioles will increasingly use other tree species.  However, a large poplar plantation will take many years to establish, and no small amount of money.  Whatever the solution, time may be the limiting factor.

Saturday, 18 June 2011

Manx joeys

Was it a dream or did I just see an orchid meadow being grazed by Wallabies? No, I've been on the Isle of Man and my collection of British wildlife poo has just increased by one. A population of around 100 Red-necked Wallabies is now claimed after an initial accidental release of a pair from a nearby wildlife park around 1970.  There are surely more; we easily saw at least 5, including young, and there were droppings everywhere. There is a relaxed view on the presence of these animals. They appear to be mildly beneficial through their grazing activities - at the moment! They are certainly amusing, hiding low in vegetation before bounding away at the last moment, thumping the ground.

This was the beginning of a 4-day tour of the Isle of Man looking at some key conservation issues. Choughs are doing well on the island; around 160 pairs. Where natural cliff sites are absent, the birds are known to nest in artificial sites. However, of interest is the recent use of active farm buildings, such as barns, rather than disused or derelict buildings. Nesting birds are being carefully monitored by Manx Birdlife.

In contrast to the tolerance of wallabies, a Brown Rat control programme to benefit breeding seabirds has been progressing on the Calf of Man. After becoming extinct on the island that gave them their name, Manx Shearwaters returned to breed in 2000. With a reduction in Rats, the population has increased to around 100 pairs. Total eradication of rats must surely be the aim to maintain this iconic bird on the island.

At Close Sartfield meadows excellent restoration work by the Wildlife Trust using green hay following scrub removal has created the spectacle of thousands of orchids of six species.

The uplands hold Curlews, Red Grouse and a good, but declining, population of Hen Harriers. Looking at various areas of moorland, we stumbled (literally) over good numbers of Lesser Twayblade and also abundant Moonwort around the old lead mines.

Below - nestbox (upstairs Chough, downstairs Muscovy Duck), Choughs calling to young, ringing young Chough (under licence).

Sunday, 12 June 2011

Spice up your reedbed.

More thinking about water level manipulation this week, back down at Ham Wall in Somerset. Reedbeds can be dull one-dimensional places for the visitor. Wet reedbeds in particular have just a few specialist species, most are generally difficult to see. This was evident at Ham Wall; Bitterns boomed and occasionally flew by, Water Rails squealed, Bearded Tits pinged and Reed Warblers jiggy jig jigged, but good views of any were few and far between. The open waters held a few common birds; Great Crested Grebes, Dabchicks, Pochards and Tufted Ducks, all with broods.

Another range of waterbirds prefer a more open, shallower habitat within the reedbed, and this can be created by keeping water levels lower and opening up the reed by grazing or cutting. One such area held Garganey, Shoveler, Gadwall, Little and Great White Egrets, Redshank, Lapwing and a migrant Dunlin. The margins of these open areas also provide good feeding areas for the likes of Bearded Tits and Bitterns.

Ideally for the visitor, a reedbed reserve should be multi-dimensional: having both high viewpoints over and into the pools, and low, close viewpoints into the reedy habitat. In addition, a mosaic of diverse habitat structure, created by water manipulation and grazing will help get the most out of a site for both wildlife and visitors.

Ham Wall continues to impress, with the key reedbed birds increasing in number and the tantalising prospect of colonisation by a greater range of southern species.

Monday, 6 June 2011


Snipe, Corn Bunting, a flowery machair field and an iris bed harbouring a Corncrake.

The month ahead looks busy, with visits to a number of far-flung sites in the UK, some new and some old favourites. The month started with a quick tour of Scotland, including a trip across to North Uist and Benbecula. Walking through the machair of North Uist is a revelation compared to breeding wader sites in the south of England; there are birds everywhere. Lapwing, Snipe, Dunlin, Redshank, Oystercatchers and Ringed Plovers all giving the tell-tale alarm calls of nesting activity in contrast to the depressing quietness of some recent visits to ‘wet’ grasslands down south.

So what is machair and why is it so good? Machair consists of a mosaic of dry and damp semi-natural grasslands, marshes and standing water. It has developed as a result of the combination of soils derived from wind-blown shell sand, a wet, windy climate and low-intensity crofting agriculture.

The waders of the machair are of very high conservation value, the first full survey of the Uists in 1983 estimated that it supported at least 17,000 pairs of the six main species. Significantly, the Uists have no native terrestrial mammal predators. Unfortunately, humans have introduced several potential predators, including Brown Rats, Hedgehogs and Mink. However, there have been various attempts to remove these. Strangely for southern eyes, Little and Arctic Terns also nest in loose groups across the fallow machair fields, forsaking the nearby glorious shell sand beaches. No doubt another effect of the lack of ground predators.

Apart from waders there is plenty to see. The flower-rich fields support huge numbers of orchids including the endemic Hebridean Marsh Orchid. With 100 or so male Corncrakes on North Uist, it was not a surprise to hear one calling from just about every bit of suitable habitat. Other highlights included Red-necked Phalaropes, Golden and White-tailed Eagles, 3 species of diver, Pomarine Skua and Bonxie, breeding Whooper Swan, Hen Harriers, Twite and Corn Buntings everywhere.