Oysterbeds Update mid July 2014 – Chris Cockburn

Hello folks

The majority of the black-headed gull youngsters are now fledged and the numbers of family groups have started diminishing. Productivity is estimated to be at least 1.5 fledged birds per pair. However, some pairs have not produced any young, indeed may not even have laid any eggs; but, their magnificent nests are a sight to behold.

The Mediterranean gulls have been less successful with only three of the original nine nest sites having broods (of 2, 2 and 1 youngsters). The poor overall productivity may be explained by the fact that some of the original pairings were of adult and 2nd summer birds. It has also been a relatively dry spring/summer and earthworms may be hard to find.

The common terns might be heading for a disastrously poor breeding season. Common tern AONs (Apparently on Nest) were seen in late May and reached a peak of c96 AONs by 26 Jun with a few very recently hatched chicks seen on 30 June. Recently, no chicks have been seen and on most days apparently -new pairs of terns have been seen displaying, showing post-breeding moult behaviour etc while some have started (re-started?) nesting activity. It is possible that these pairs have lost their first egg clutches  and are attempting to re-lay. To add to their problems, many nests were flooded out by the recent surging tides (particularly the tides of 13 & 14 July). The behaviour is not easy to explain without closely inspecting the nests.

The most likely cause is either predation of eggs/small chicks or that the adults are not in good breeding condition. The most likely predators are either failed Mediterranean gulls, which have been regularly flying “low & slow” over the colonies and even strolling about on the islands, or rats, which were the cause of nest failure in 2005 & 2006. The common terns were very late in starting to nest, indicating a food problem in the harbour and with frequent windy conditions making it difficult for the terns to catch prey fish, it is quite possible that they are not in good breeding condition.

The pair of oystercatchers that started nesting on June 23 failed after only eight days, almost certainly due to predation of eggs. The main suspects are Mediterranean gulls; but rats might be the culprits (swimming out at night when wind speeds drop).

Meadow Browns and Marbled Whites are still around in large numbers on the Billy Trail; there are increasing numbers of Small & Green-veined Whites, Commas and Red Admirals while fresh Peacocks, Small/Essex Skippers and Gatekeepers are appearing. There are abundant nectaring sources from the profusion of flowering Bedstraw, Tufted vetch, Meadow vetchling, Knapweed, Rampion, Teasels, Bramble etc.

Regards

Chris C

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