Mountain chiffchaff Caucasus, but interbreeding occurs rarely, if ever. The mountain chiffchaff differs from "tristis" in vocalisations, external morphology and mtDNA sequences. Its two subspecies appear to be distinct vocally, and also show some difference in mtDNA sequences. Mountain chiffchaff The mountain chiffchaff or eastern chiffchaff ("Phylloscopus sindianus") is a species of leaf warbler found in the Caucasus ("P. s. lorenzii") and Himalayas ("P. s. sindianus"), and is an altitudinal migrant, moving to lower levels in winter. The nominate subspecies is similar to the Siberian chiffchaff, but with a finer darker bill, browner upperparts and buff flanks; its song is almost identical
Genomic evolution of birds possibility of genomic expansion in mammals and reptiles. Also, there is no such genomic loss in any vertebrate group as great as that of birds. Its possible that the early chromosomic fragmentation event that lead to the appearance of microchromosomes in birds significantly contributed to this gene loss. These fragmentation events must have taken place in a common ancestor of most birds, since approximately every two out of three species studied have at least 30 pairs of microchromosomes, 2n = 80 being the size of the average karyotype of birds (with the only exception the family Falconidae, which are 2n