Sequencing of a partial fragment of the ND5–cytb mithochondrial genes (1553 bp) and its nuclear copies was carried out to Phylloscopus borealis sensu lato, belonging to individual taxonomic groups from different parts of the range. It was shown that the majority of taxon-specific and unique mitochondrial substitutions in examinandus and xanthodryas forms were identical to those in nuclear copies of borealis mtDNA. Differences between mitochondrial haplotypes of examinandus and nuclear copies of mtDNA borealis were low (p = 0.02), at the same time the mtDNA genetic divergence in borealis–examinandus, borealis–xanthodryas and examinandus–xanthodryas significantly exceeded this value (p = 0.035, 0.044 and 0.046, respectively). A nuclear copy of the mitochondrial haplotype of the easternmost form of xanthodryas was first discovered in the nuclear genome of one borealis individual in the western part of the breeding range (Komi Republic). Alongside this, it was shown at the first time, the nuclear copies of xanthodryas mtDNA from Toyama Prefecture (Japan) were close to the mitochondrial haplotypes of borealis from Kytlym (Sverdlovsk region) (p = 0.018). Thus, the mutations emerging in the nuclear copies of mitochondrial genes are the source of most substitutions in the mitochondrial DNA of the studied forms. The origin of the mitochondrial haplotypes examinandus and xanthodryas from nuclear copies of mtDNA borealis and the close similarity of their nuclear genomes gives grounds to consider the mitogenomes of these forms as variants of the haplotype of the single species Ph. borealis sensu lato. With a high degree of probability, it can be argued that the divergence time of the haplotypes of the analyzed forms is significantly less than 2.5-3 million years, as previously assumed by a number of authors [Saitoh et al. 2010; Alström et al. 2011], and the “molecular clock” that do not take into account recombination events between the nuclear and mitochondrial genomes cannot be used in this case.