Last night we went to Strumble Head for the first Storm Petrel ringing of the season. Five were caught and ringed.
Storm Petrels are difficult to age and sex and there is much debate ongoing over the reliability of criteria used. A paper written in 2001 is an interesting read.
M. Bolton & R. Thomas (2001): Moult and ageing of storm petrels hydrobates pelagicus , Ringing & Migration, 20:3, 193-201
Moult in Storm Petrels is mainly undertake at sea during migration and in winter quarters. To minimise the effect of missing feathers on flight efficiency the replacement of each feather tract is protracted so each full moult takes many months to complete.
After a careful look at the moult in the birds we caught, they were all aged as 4's, born before this year.
Mixed aged feathers were easy to see in the secondaries of some of the birds.
It was one of those nights where you go home inspired to find out more about these interesting birds.
For more pictures see Adrians Strumble Head Seawatching blog.