Background

In western Europe, tristis is regarded the rarest of the three taxa. Song (eg, Martens & Meincke 1989) and calls (eg, Constantine & The Sound Approach 2006, van den Berg & The Sound Approach 2009) are nowadays regarded as diagnostic and suffi ciently distinct to separate it from the two other taxa (Constantine & The Sound Approach 2012). But what about nonvocal birds? Plumage characters to distinguish tristis from nominate collybita are described by, eg, Svensson (1992), Dean & Svensson (2005), Svensson et al (2009), van den Berg & The Sound Approach (2009) and Ebels (2009). Tristis is regarded as the subspecies with the least amount of green and yellow in the plumage. Typical birds are brown and many birds are grey, without yellow or green tones on upper and underparts. Nominate colly bita has the most green and yellow tones in its plumage. Abietinus is often considered to be in termediate between the two by Dutch ringers but in fact Svensson (1992) explains that abietinus and collybita generally are impossible to separate when handling single birds (see also Cramp 1992). He mentions that, on average, collybita is ‘very slightly more green and less grey above’and that ‘underparts are said to be more yellow and buff than in abietinus’ but adds that he finds it difficult to confirm these differences and that ‘individual variation seems to be just as pronounced as geo graphical’. However, both Cramp (1992) and Svensson (1992) mention that abietinus is ‘a trifle’larger than both collybita and tristis but, because of extensive overlap, this does not present much help in identifying abietinus by ringers either. As far as the current knowledge goes, only complete ly brown or grey (nonvocal) chiffchaffs can be safely identified as tristis. In practice, however, many tristis do have some green on the upperside or yellow on the supercilium, underparts and bare parts (eg, van den Berg & The Sound Approach 2009). But, because of its alleged rareness,‘safety first’is the widely accepted view on the identifica tion of tristis. For example, the CDNA does not accept records of nonvocal chiffchaffs that have green or yellow in their plumage, despite the plumage analyses in van den Berg & The Sound Approach (2009) of birds trapped and photo graphed by Arend Wassink in Kazakhstan.

As a result, many Dutch ringers until recently identified birds less green and yellow than nomi nate collybita but with some yellow on the under parts and/or supercilium and/or green on the man tle as abietinus, simply because the amount of yel low and green supposedly ruled out tristis. Levering & Keijl (2008), for instance, list for 1970 2006 79 abietinus trapped and ringed at Castricum, NoordHolland, and 26 birds ‘showing features’ of tristis (not a single one being accepted). Likewise, Blom et al (2011) list 16 abietinus and five tristis trapped and ringed at Westenschouwen, Zeeland, in 1959 2009. However, recent publications led some ringers to challenge these results and to inves tigate newly trapped birds by using DNA analyses.