Salty or sweet Sir?

Redshank, Black-tailed Godwits, Ruff and Dunlin feeding on the lagoon at Conwy as the water drops to a suitable feeding depth; Ragworm or bloodworm, which looks tastiest?

At what salinity should coastal lagoons be kept to maximise bird use? Coastal lagoons have a salinity that will vary between seawater (at 35 parts per thousand (ppt)) and fresh (1 ppt). The salinity will influence the invertebrates that dominate the lagoon and therefore the birds that are found there. This week I visited Conwy in north Wales where a proposal to change the lagoons from fresh to saline is being considered. How might this affect the birds that feed on the lagoons?

Low salinities (less than 8 ppt) will favour non-biting midges (chironomids) in the mud, with water boatmen (corixids) and opossum shrimps in the water. At higher salinities (8-40 ppt) ragworms Nereis and mud shrimps Corophium will join the chironomids and the shrimp Palaemonetes varians may be abundant in the water. The maximum biomass of the chironomid/corixid and ragworm/shrimp fauna will occur at about 6 and 24 ppt respectively.  However, the other key factor for attracting birds is the water level.  Good numbers of birds will only occur if the prey items are available at suitable water depths so good control of the water levels is desirable.

At Minsmere, various parts of the scrape are kept at different salinities; North Girder (in front of South Hide) at 15-35 ppt, whilst East Scrape is usually less than 15 ppt. The freshest scrapes (eg West) can become dominated by aquatic vegetation such as Mare’s-tail; an occasional dosing with salt water will sort this out. Switching between high and low salinities will kill off invertebrates. However, most of the less specialised invertebrates can re-colonise rapidly. Such switching may be useful as an occasional management tool but not on a regular basis.

The excellent scrapes at Cley are fed by fresh water draining from higher land, and are usually less than 1 ppt. However, high tide surges can bring an incursion of saltier water. Vange Marsh in south Essex, a seriously good addition to the scrape world, is also kept at a low salinity, usually less than 5 ppt, attracting sandpipers, shanks and godwits.

Last Friday I was at Havergate Island, where the lagoons support scarce lagoon invertebrates such as the Starlet Sea-anemone. Here the invertebrates rather than the birds determine the water regime as the salinity needs to remain in the favoured range of 25-40 ppt for these lagoon specialists. The lagoons did however, hold hundreds of birds, including 14 Spoonbill, 350 Avocets as well as numerous Knot, Black-tailed Godwits, Dunlin, Grey Plover and Redshank.

Below - How many Starlet Sea-anemones can you see?

Mecca?

A dull East Bank, a great scrape; the Ruff and the smooth.

A weekend up in north Norfolk, the first for a while, brought on a bit of reminiscing as I walked around Cley, a place that, for a while, I seemed to visit nearly every weekend. I remember getting my newly published copy of ‘Where to watch birds’ back in the late 60’s and reading the following description of Cley:

“There can hardly be a serious bird-watcher in the country who has not made the pilgrimage to Cley. It has been the Mecca of ornithologists for the last 140 years...” wrote John Gooders, continuing ...”the East Bank at Cley is the best place in England to see passage waders – and to meet well known bird-watchers”.

I visited Cley soon after, on a YOC trip, meeting both Richard Richardson and Billy Bishop, but it was the couple of hours in the company of RAR on the East Bank that was truly inspiring as he seemed to magic birds out of thin air for us. My first solo trip to Cley was in 1970, and by chance, RAR was in a car that stopped for me as I hitch-hiked the final leg along the coast. The trip to Cley was to become a regular birding weekend over the following years and the walk around the Cley 'square' to became a favourite.  Many good birds were seen, with Caspian Tern, Red-throated Pipit and Black-headed Bunting amongst the better of my 'self-founds'.

Forty years on, Cley still delivers. Last weekend I saw plenty of passage waders (but there was a scarcity of well known birders, well, any birders in fact). Three Wood Sands, 2 Little Stints, Ruffs, Knot, Spotshanks, Greenshanks, numerous Dunlin, Whimbrels and godwits, and 9 Spoonbills were amongst the many birds on show. The scrapes looked in great condition, the hides blend nicely into the landscape and there’s a nice modern eco-centre containing a good range of books. I renewed my lapsed NWT membership, after all it’s only half the price of a tank of petrol.

But the walk around the ‘square’ is not what it used to be. East Bank is, well, dull, although Arnold's still produced as good a range of birds as any other pool. A bench has replaced the old flattened grass – and more than accommodates the number of birders there. A good walk should have points of interest along the way; variations in habitat, pools, openings, viewpoints etc, but those that previously existed, and the hides off the bank, have long since been removed or allowed to grow over.   Most disappointing of all, there is little sense of the history of this place. A few named hides or pools, and just a faded plaque for RAR on an obscure back wall. What could this place be like with a bit of imagination in both site layout and interpretation? This could be a birders Mecca, but currently it's just a well managed reserve with barely a nod to its past.

Returning home, I flicked through the pages of ‘Cley Marsh and its Birds’ by Billy Bishop and arrived at the page where he recalls a letter received from Lord Buxton in the 60’s. It seemed worth sharing. Lord Buxton writes:

“Within an hour I was sitting in the boat house watching a bittern boom – the very thing I had yearned to see for decades. But it was quite a shock. All the famous descriptions by experts were proved phoney. Quite honestly I was a bit embarrassed at first, because the bittern looked as if it was blowing off through its backside. This seemed rather a tawdry climax to the greatest discovery on earth and I wondered in what language I was going to announce it to the world!”

That Bitterns fart, rather than boom, is still a closely guarded secret.