Richard Klim
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In the latest Dutch Birding, Arnoud van den Berg (almost?) proposes species status for Phylloscopus collybita tristis:
Ref: van den Berg, AB 2009. Calls, identification and taxonomy of Siberian Chiffchaff: an analysis. Dutch Birding 31(2): 79-85.
Richard
Ref: van den Berg, AB 2009. Calls, identification and taxonomy of Siberian Chiffchaff: an analysis. Dutch Birding 31(2): 79-85.
"New taxonomy and discussion
There is no genetic proof that western tristis or 'fulvescens' are hybrids and more closely related to abietinus than to eastern tristis. Although just a few birds were sampled, Helbig et al (1996) only found evidence of gene flow between nominate collybita and abietinus, and not between tristis and abietinus. Therefore, the idea that there is a wide zone of hybridization between tristis and abietinus must be regarded as hypothetical. It is presumably based upon the cline in colour within the range of tristis, or perhaps upon the incidence of mixed-song which, by definition, is more likely to occur in western areas where abietinus may turn up (Lindholm 2008).
The differentiation of mitochondrial DNA (1.7-2.0% mtDNA divergence) was not considered high enough for elevation of tristis to species level by Helbig et al (1996). However, there are other examples of species-pairs with slight genetical differences, such as the 0.4% mtDNA divergence in Pine Bunting Emberiza leucocephalos and Yellowhammer E citrinella (Almström et al 2008). Based upon the differences in vocalizations, one can conclude that tristis and Common Chiffchaff are not part of a cline either while hybridization may occur much less frequently than generally believed, if at all. To judge whether tristis and Common both represent a different evolutionary lineage, George Sangster (in litt) suggested that it is more important to look for a constant phenotype or consistent characters of collybita and abietinus and of tristis in areas away from the contact zone than to analyse what is happening in that zone. In this respect, the fact that Martens & Meincke (1989) demonstrated that east of the Ural mountains just one song occurs, ie, the distinctive tristis song, appears relevant.
On present knowledge, the most practical taxonomic working hypothesis is that tristis concerns a species showing slight morphological variation, becoming browner and less yellow and olive from west to east, and distinct from Common Chiffchaff in song and calls (Martens & Eck 1995, cf Dean & Svensson 2005). Some western tristis may approach abietinus in plumage coloration, which renders sounds as the most objective and reliable identification feature. ..."
There is no genetic proof that western tristis or 'fulvescens' are hybrids and more closely related to abietinus than to eastern tristis. Although just a few birds were sampled, Helbig et al (1996) only found evidence of gene flow between nominate collybita and abietinus, and not between tristis and abietinus. Therefore, the idea that there is a wide zone of hybridization between tristis and abietinus must be regarded as hypothetical. It is presumably based upon the cline in colour within the range of tristis, or perhaps upon the incidence of mixed-song which, by definition, is more likely to occur in western areas where abietinus may turn up (Lindholm 2008).
The differentiation of mitochondrial DNA (1.7-2.0% mtDNA divergence) was not considered high enough for elevation of tristis to species level by Helbig et al (1996). However, there are other examples of species-pairs with slight genetical differences, such as the 0.4% mtDNA divergence in Pine Bunting Emberiza leucocephalos and Yellowhammer E citrinella (Almström et al 2008). Based upon the differences in vocalizations, one can conclude that tristis and Common Chiffchaff are not part of a cline either while hybridization may occur much less frequently than generally believed, if at all. To judge whether tristis and Common both represent a different evolutionary lineage, George Sangster (in litt) suggested that it is more important to look for a constant phenotype or consistent characters of collybita and abietinus and of tristis in areas away from the contact zone than to analyse what is happening in that zone. In this respect, the fact that Martens & Meincke (1989) demonstrated that east of the Ural mountains just one song occurs, ie, the distinctive tristis song, appears relevant.
On present knowledge, the most practical taxonomic working hypothesis is that tristis concerns a species showing slight morphological variation, becoming browner and less yellow and olive from west to east, and distinct from Common Chiffchaff in song and calls (Martens & Eck 1995, cf Dean & Svensson 2005). Some western tristis may approach abietinus in plumage coloration, which renders sounds as the most objective and reliable identification feature. ..."
Richard
