There are eleven species of bushtits or long-tailed tits divided into four genera, all but one of which are found in Eurasia. They are active birds, moving constantly while foraging for insects in shrubs and trees. Several species display cooperative breeding behaviour. Hybridization has been documented in one genus, Aegithalos.
Phylogenetic studies found very low interspecific distances between Black-browed Tit (A. bonvolati) and Sooty Tit (A. fuliginosus) based on mitochondrial markers (Packert, Martens & Sun, 2010; TIAN et al., 2010). Coalescent analyses indicated historical introgression of mtDNA from Sooty Tit into Black-browed Tit, while gene flow at autosomal and Z-linked loci was negligible (Wang et al., 2014). However, another study, using RADseq data, uncovered bi-directional nuclear gene flow (Zhang et al. 2017).
Packert, M., Martens, J. & Sun, Y. H. (2010). Phylogeny of long-tailed tits and allies inferred from mitochondrial and nuclear markers (Ayes: Passeriformes, Aegithalidae). Molecular Phylogenetics and Evolution 55, 952-967.
TIAN, H., ZHANG, Z., Yan, H. & Fumin, L. (2010). Molecular phylogenetic analysis among species of Paridae, Remizidae and Aegithalos based on mtDNA sequences of COI and cyt b.
Wang, W. J., Dai, C. Y., Alstrom, P., Zhang, C. L., Qu, Y. H., Li, S. H., Yang, X. J., Zhao, N., Song, G. & Lei, F. M. (2014). Past hybridization between two East Asian long-tailed tits (Aegithalos bonvaloti and A. fuliginosus). Frontiers in Zoology 11.
Zhang, D., Song G., Gao B., Cheng Y., Qu Y., Wu S., Shao S., Wu Y., Alström P., Lei F. (2017). Genomic differentiation and patterns of gene flow between two long‐tailed tit species (Aegithalos). Molecular Ecology 00:1-12.