Trip reports

Indoor Meeting - The Lesser Black Blacked Gull

Indoor Meeting - The Lesser Black Blacked Gull
rspb images

Friday, 16 September 2011

Currently gulls are classified traditionally - do they look alike, have the same habits etc. But now DNA analysis and the fossil record are helping to derive a more precise classification. They are strangely, members of the shore birds which include for example oyster catchers and they evolved in the Cretaceous period between 145 and 65 million years ago (give or take half a million)
The laridae family which include gulls, terns, skimmers and auks split off some 20 million years ago.
There are 3 subspecies and ours is the Larus Fuscus. It is slightly smaller than the herring gull. and is now causing concern. It's numbers are falling and the number of sites contracting. Indeed one site - Walney Island in Cumbria - holds one third of the UK population!
They generally start breeding at 5 years and an average lifespan is 15 years, although the oldest on record is 30 years, 4 months which was ascertained when the bird was shot. They are generally faithful both to their nest site and their partner.
The gulls have been there since 1954 and currently there are about 4000 prs. nesting along with 400 prs of herring gulls. With little predation the population has increased to it's present size following a drop to 1500 prs. in the botulism outbreak of 1990. Food is plentiful - Lamby Way tip and as far afield as Bristol and Gloucester tips.
Viola gave us some fascinating details She monitored 714 nests with 1961 eggs. The mean clutch size was 2.8 with a success rate of 65% The size of clutch is affected by the quality of the nest and the vegetation nearby. Nests in the middle of the colony are usually poor, badly built with no vegetation to protect them and have smaller clutches, smaller eggs and a worse success rate. Also when the eggs hatch is important. Too soon and they may be predated by gulls with as yet no chicks. Similarly if they hatch late. Ideally they need to hatch about 3 weeks into the hatching period when other gulls are busy with their young.
They migrate. A bird ringed on 3rd July on Flat Home was in Northern Spain on 20th August but now, rather than relying solely on colour ringing birds are being fitted with satellite tags - not many yet, they cost £1000 each. They are solar powered and weigh less than 3% of the birds body weight and are attached by a small harness. At Orfordness reserve in Suffolk 11 birds were tagged and later recaught. Of these only 5 had working tags. Of the rest 4 were lost or damaged, one died and one had no records.
The results from these 5 birds were fascinating. They travelled between 4000 and 13000 Km. On the outward journey the least time was 15 days and the longest 155. On the way to their wintering grounds which for one was as far as Morocco (this was the one that didn't come back) they generally flew straight across the Bay of Biscay. Some would stay for days in France, others gave it a miss. There was no particular pattern to their itinerary. On the other hand most birds returned along very similar routes - crossing the Bay again and spending similar lengths of time stopping on passage. The longest duration was 17 days and the shortest 11 days.
Not only did Viola give us some fascinating information but the graphs were beautifully clear and easy to understand and their were some good photos including ooh aah chicks.