Those parts of the reserve around the sewage treatment works are attractive to late passage and wintering Chiffchaffs (Phylloscopus collybita), with over 100 being ringed annually during the winter months in recent years . A number of birds showing the characteristics of the eastern race, known colloquially as “Siberian Chiffchaff” (P. collybita tristis), are recorded annually with at least six different individuals being recorded during the winter of 2014/15. Establishing the status in Britain of “Siberian Chiffchaff” has long been problematic. Key to this problem is the correct identification of the form and the difficulties of separating true Siberian tristis, largely from east of the River Yenisei, 3,000 km east of Moscow, and hybrids, colloquially known as ‘fulvescens’, from the West Siberian Plain, 1000 km east of Moscow, from abietinus, from Scandinavia and western Russia west of the Urals continue to plague both observers and records committees. A suite of biometric measurements has been taken from trapped tristis type birds at South Milton Ley and any feathers shed during the ringing process have been sent to Professor Martin Collinson at Aberdeen University for DNA analysis.
The first Siberian tristis Chiffchaff in Devon to be confirmed by mDNA analysis was trapped at South Milton Ley on the 26th November 2015 and Martin Collinson commented: “its cytb DNA sequence is with 100% certainty that of a tristis – only 1 p different from a sequence found in the core Yenesei region and other Sibe Chiffies we have recently sequenced from Western Europe.”
Subsequently, given the view that if it looks like a tristis and sounds like a tristis then it probably is a tristis, samples have only been sent for analysis from birds showing some divergence from a classic tristis. The features shown by these birds would prevent them from being accepted using the criteria currently employed by Devon Birds and would have relegated them to the intergrade “fulvescens” category. To date, feathers from two of these birds have been analysed and both have been confirmed as 100% tristis.
Photos of most of the birds identified as tristis in recent years can be seen here: Siberian Chiffchaffs at South Milton Ley