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.

Redpolls

At least 20 redpolls have been feeding in the garden on nyjer over the last month.  A variable bunch from classic Lesser through to Mealy. A selection of photographs shows some of the variation but by no means all.

To feed or not to feed?

The recent severe weather has been tough for Bitterns, with many being seen around the remaining areas of unfrozen water, frequently in unusual situations.  Bitterns traditionally suffer in such cold winters.  At least 17 sites attempted to feed their Bitterns, usually with Sprats or Sardines, during the coldest spell of weather and 8 sites report that Bitterns were seen taking the fish. See Steve Blain's video of a Bittern eating sprats  (or below) provided by local birders at Stewartby Lake.  At Leighton Moss, three Bitterns came to the feeding site regularly (about once every half hour), took some fish and then returned regularly during the day.  At most of the other sites, Bitterns were seen in the vicinity of the food and may well have taken it.  So it would appear that feeding in hard weather may help some Bitterns survive.  We feed Blue Tits, so why not a bird that is a conservation priority in the UK?


On the other hand, is this just another example of unnecessary human tinkering?  Will it make any difference at all to the population in the coming spring, or will it even hinder a natural dispersal of young birds to new sites?  What do you think?

Edit - In a rather low poll, 16 out of 16 respondents thought we should be feeding Bitterns.

Bittern eating sprats from Steve Blain on Vimeo.

Exodus

A traditional New Year’s Day thrash through the valley yielded a meagre return of 85 species. Rather than delivering a load of more unusual birds, the recent cold weather appears to have prompted a mass exodus instead. With most pits still largely frozen duck numbers are very low. With a valley total of around 12 Smew, 8 Bitterns and 50 Goosander, numbers of these cold weather specialists are barely above average. Long-staying single Pink-footed Goose and Red-breasted Merganser, along with a couple of flocks of Waxwings, the bird of the winter, were about the highlights. Kingfisher, Chiffchaff, Snipe, Cetti’s Warbler and Little Egret remain distinctly difficult to find.


Holyfield Marsh: 2 Smew, 6 Goosander, Pink-footed Goose.
Cheshunt GP: 2 Bitterns, 2 Smew, 60 Siskin, 5 Water Rails.
Girling Res: 12 Black-necked Grebe, 2 Green Sandpiper, 5 Goosander, 21 Goldeneye, Tufted/Pochard hybrid.
Waltham Abbey: 5 Waxwing.
Rye Meads: Shelduck, Cetti’s Warbler, Bittern.
Amwell: 3 Smew, 2 Woodcock, Pintail, Little Egret.

What's happened to cold weather?

R-b Merg on the KGV, packed-in Tufties at Nazeing and Smew at Cheshunt.

What’s happened to cold weather? When we had it in the 80’s we were splattered in scarce grebes, divers, gulls and other stuff. This winter has been rather slow, a few Bitterns and Smew (but barely more than usual) and not much more so far. Okay, there were some Eider on the Girling today, and we are knee-deep in Waxwings, but overall it’s not like it used to be.

In early 1979, strong north-easterly winds precipitated a remarkable influx of, amongst other birds, grebes, divers, Smew and Goosander. Within a month my Lee Valley list included 12 Red-necked Grebes, 30+ Red-breasted Mergansers, 2 Slavonian Grebes, 2 Black-throated, 2 Great Northern and a single Red-throated Diver, 26 White-fronted Geese, Hen Harrier, 5 Long-eared and 6 Short-eared Owls.

Likewise, in early 1985, severe weather resulted in a massive influx of Smew (up to 40 at Holyfield Marsh alone), Scaup (9), Slavonian Grebes (5), Red-necked Grebes (4), Velvet Scoter (3), Long-tailed Duck, Bean Goose, Glaucous Gull, Shag and Hen Harrier. However, judging by the length of my notes, a Mediterranean Gull was the most exciting.

Is this current weather not blasting easterly enough, has climate change shifted the distribution of some of these birds, or are there just fewer of them nowadays? Or perhaps a bit of all three?

Cold weather refuges are critical for wintering waterbird populations. These may be provided by the larger, deeper waters of the reservoirs that rarely freeze, or by sites that have flowing water, such as the rivers or the sewage treatment lagoons at Rye Meads. The winter of 2008/09 provided an opportunity to record hard-weather effects in the valley during the short freezing spell in early January. At this time, up to 2,000 birds may have left the valley, with around 1,000 returning as milder conditions prevailed. Dabbling duck were mainly affected with losses of Gadwall, Teal and Shoveler but significant numbers of Coot also left. Birds also re-distributed; Gadwall concentrated on Netherhall GP and the King George V Reservoir, as sites such as Amwell NR, Holyfield Marsh GP and Cheshunt GP froze over.

Revision of the 30 cm rule.

A Bittern nest at Ham Wall; built in 110cm of water

 It is perhaps surprising to think that until the early 1990s we knew little about the ecological requirements of the Bittern other than it was a ‘reedbed bird’. With the UK population plummeting, research was undertaken at the key sites: Minsmere and Leighton Moss. It soon became clear that it was the drying out of our reedbeds through natural succession that was the main cause. Put simply, Bitterns require wet reedbeds that provide both abundant food and security from predation. The research showed that female Bitterns nested in reedbeds that remained wet all summer and the average water depth on the date of the first egg was 22 cm. The call went out to create new reedbeds, with a recommended spring water depth of around 30 cm.

This week we reviewed the data from extensive reedbed studies over the last couple of years. One revealing analysis was the depth of water that Bitterns in the UK are now nesting in, and the take-home message is that Bitterns appear to be able to nest in as deep a reedbed as a site can provide. At the superb new wet reedbeds at Ham Wall, Lakenheath and Shapwick, recent nests have been constructed in 50cm to 1metre of water. Perhaps we shouldn’t be surprised; a previous Polish study found Bittern nests in up to 97cm of water.

So while the research was invaluable and set out the path for Bittern recovery in the UK, the nest water depths merely reflected the best (wettest) reedbeds at that time. Now we have better reedbeds, the 30cm rule requires revising to reflect our increasing knowledge.  New, big, wet reedbeds are not only going to last longer but will be more robust in the face of climate change and will be attractive to potential new colonists, note the presence of Little Bittern, Purple Heron and Great White Egret this year in our biggest and wettest reedbeds.

Ouse up and Ouse down?

The Ouse Washes are officially classed as ‘Unfavourable’ condition, due to the increased incidence of summer flooding and the poor water quality. Breeding waders have declined, from an overall total of 900+ pairs in 1990 to around 450 this year. Most notably, Black-tailed Godwits have declined to just 2 or 3 pairs at this former stronghold, and Snipe have also declined sharply.

However, ‘every cloud has a silver lining’ as they say. Under the wetter summer conditions, breeding duck have increased, with average counts over the last five years of 161 pairs of Shoveler, 110 of Gadwall and 9 of Garganey. Spotted Crakes also increase in the wetter years, with up to 4 ‘whippers’ in recent times. These ups and downs mirror the cyclical patterns of species seen in some natural floodplains in Europe – more ducks, grebes and terns in wet years, more waders and Corncrakes in drier years.

The influence of the water regime also applies in the winter, deep floods favour Pochard, Tufted Duck and Coot, shallow floods favour the dabblers; Shoveler, Wigeon, Pintail and Teal.  The highly mobile birds respond rapidly as the water levels change.  There are of course many external influences at work as well. Many wildfowl are ‘short-stopping’ on the continent, due to recent milder (!?) winters. The wild swans, perhaps the washes most notable winter visitors, also show differing trends, but this is not down to water regime. Whilst Whoopers (from Iceland) have steadily increased to over 5,000, Bewick’s have declined to around 3,500. The decline in Bewick’s is concerning as it is clear that poor breeding success is at least part of the cause. The number of juvenile birds accompanying the adults has sharply declined in recent years.

Today the washes were frozen stiff. Whoopers and Bewick’s fed out in the adjacent beet fields, returning in the late afternoon to roost on a small area they keep ice-free. Around 1600 have returned so far this winter. It may be ‘unfavourable’ but the Ouse Washes are still a fantastic place for birds.