Saturday, 17 December 2016

Skokholm Great Black-backed Gulls

Great Black-backed Gull W:099 (HT94962) seen at Wisemans Bridge yesterday was ringed as a fledgling on 21st June 2015. It has been seen before, by Pamela Marshall at Saundersfoot Harbour (just next door to Wisemans) on 2nd September 2016. Of 44 fledglings ringed on Skokholm in 2014, 24 have been seen elsewhere (over a quarter of them in Cornwall). Ten of the 44 definitely survived their first full year after fledging (based on ring resightings away from the Island). Four of the 44 have definitely survived to two years of age. Of 52 fledglings ringed in 2015 (including the bird seen by Pam and Toby), eight definitely survived their first full year.

We rely on colour ring resightings such as this to help us understand juvenile survival. Adult survival is relatively straight forward for us to calculate as the colour ringed birds return to Skokholm each year for the breeding season (over 90% of adults survived between the 2015 and 2016 breeding seasons). Perhaps the youngsters will also breed there one day (allowing us to improve our survival estimates) but many may select other colonies. So please keep the sightings coming in. If anyone fancies a really productive bit of birding, then track down your local Great Black-backs and check them for rings (even a count of birds which definitely didn't have rings would be interesting in a Pembrokeshire context).
W:099 at approximately 16 months old. If you get to see what the gulls are feeding on then this would be great to know too. (c) Pamela Marshall