Wetland Bird Surveys

It was a weekend of wetland bird surveying for the BTO’s nation-wide WeBS monitoring scheme. On Saturday I was completing the WeBS in Chichester Harbour. The area covered was between Itchenor and Dell Quay. The count started in Itchenor. The tide was rising, and at a wader roost site the amount of available land was decreasing. As we counted, more and more waders continued to fly in and pile into the ever-diminishing area of land. What originally started out as just 13 visible redshanks and 20 grey plovers ended up being over 200 redshanks and 400 dunlins in addition to the grey plover! One of the grey plovers was in full, spectacular, summer plumage. Unusual for December!

North of Chichester Marina a great northern diver was working its way up the channel close to the near bank. For the brief periods between its dives we had fantastic views of this large loon. Great northern divers typically have large square-ish heads, this one was no exception and had a ginormous cube between its chunky bill and neck.

On Sunday it was WeBS at RSPB Medmerry. As has often been the case recently it was rather blowy. The wind was gusting around 40 miles per hour. This is not ideal condition for counting birds or anything else for that matter…

The most notable count from the day was that of the teal. They didn’t reach the totals attained last year when there were over 2,000 on the site, but numbers were still reasonable with around 1,000 birds seen. As I was counting through a flock of 450 teal a strikingly pale individual caught my attention. Around half of its face was white and there was a significant amount of white running down the back and sides. But it was a teal, it just had abnormal areas of plumage.

Distant picture of unusual teal at Medmerry.

There are several different causes of white feathering in birds. The most well known would be albinism, this is caused by a genetic mutation that halts the production of melanin. Melanin pigments are dark, so a systematic reduction in melanin synthesis causes albino birds to be entirely paler than non-albino. Another cause of abnormal colouration is leucism. Leucism is resultant from developmental defects in pigment-producing cells; it does not necessarily cause a system-wide reduction in pigment. The resulting effect therefore can vary from small patchy areas of abnormal colouration to something so widespread that it could resemble albinism. This teal appeared to fit the criteria for being leucistic however there are many other potential causes, nothing is cut and dry when it comes to biology!

Common snipe were recorded on both days in low numbers, at Medmerry just one was seen. Contrast this with just over a week prior when a farmland bird survey at the same site revealed 6 jack snipe and 107 common snipe. The methodology for the farmland survey verses the WeBS is quite different, and this is the reason for the disparity in the numbers (rather than almost all the snipe having disappeared in the meantime!). It is difficult to know the true number of individuals of camouflaged and reclusive species such as snipe, and a WeBS count will almost always undercount these birds. With a monitoring scheme such as WeBS some important pieces of information are to be found in the trends. From this perspective being consistent with the recording, more so than being 100% accurate, is the aim.

- Hugh Baggaley