Wednesday, 14 June 2017

Cormorants on St Margarets Island

Four members of the Pembrokeshire Ringing Group visited  St Margaret's Island yesterday to carry out the annual ringing of Cormorant chicks and successfully ringed 87 chicks.  But they found a scene of devastation too with at least 60 large nestlings found dead on the nests following the bad weather last week.  They were all of large size with 20=35% covering of feathers but the rest of the body covered in down. They would have been too big to be brooded and covered by their parents so in the torrential downpours we experienced in the last 10 days they would have got completely sodden and with the strong winds succumbed to the cold.  Many nests contained one or two dead chicks draped over the nest cup.  It is possible that the parents also struggled to find food for their chicks in the bad sea conditions but in over 50 years of studies on the island this sort of mortality has never been seen before.
It is worth noting that on Thorne Island the Cormorants were around two to three weeks earlier than the St Margarets colony and were seen incubating in the second week of March and on 12th June all but three or four chicks had already fledged whereas on St Margarets most are still a couple of weeks away from fledging.   There were also some very small chicks and one nest with eggs – presumably all relays.
Anecdotal observations on both Thorne Island and St Margaret’s  was also that the numbers of Herring Gull chicks seems to be quite small so maybe the weather has created a problem for the gulls too.  A visit to Caldey this week will tell us if this is the case and the Skokholm warden is planning to look at his colonies too.