Haplotype networks constructed with nuclear loci. The three loci in the upper row (CHDa, VLDLR9 and BRM15) are Z-linked, whereas the three in the lower row (TGFB2, RAG1 and MB) are autosomal. Each circle represents a haplotype, and the size of the circle is proportional to that haplotype’s frequency. Dots represent unsampled haplotypes. Haplotypes are coloured according to taxon: black for Aegithalos bonvaloti and white for A. fuliginosus.