Red-throated diver - ages
Monday, June 7, 2010 at 5:54PM Gavia stellata
Very few observers have reported whether their sightings involved adults or immature birds, perhaps not surprisingly considering the circumstances in which they are often seen. However in the autumn it is easy to differentiate those in full summer plumage and those showing traces of summer plumage, from those in winter and juvenile plumage.
This was recorded systematically at Strumble Head during autumn passage between the years of 1980 and 2008. The proportion showing signs of summer plumage was 91 % in September, 50 % in October and 3 % in November (latest on 23 November), the total number of birds examined being 483, 588 and 533 respectively. This clearly indicates that adults pass earlier than the bulk of younger birds.
Graham Rees
(Covers records up to and including those for 2006).