The two Fennoscandian willow tit populations studied showed no phylogeographic structure (II). The same was also true for the eight great tit populations (III) and the five northernmost blue tit populations. On the contrary, the most southern blue tit population from Barcelona contained specimens widely different from the northern majority (IV).
The minimum spanning network constructed from the haplotypes of the willow tits formed a net-like structure, where the birds from the two populations were randomly distributed meaning that the populations are historically panmictic. This is supported by the observed immigration rates studied in the Oulu population and the recovery data from the Finnish Bird Ringing Center. The distribution of pairwise genetic distances was very close to the expected distribution under population expansion. The postulated expansion was further supported by the significantly negative Tajima’s D value (II).
The minimum spanning networks formed from the great tit and the ‘northern’ type of blue tit were more star-like having the central most common haplotypes. Tajima’s D values were significantly negative and the mismatch distributions followed those expected of expanding populations. This result and the presence of the common haplotypes in almost all the sampled populations support the population expansion of both species connected to the colonisation of the present distribution area (III, IV).
The blue tit population from Barcelona consisted of haplotypes that belonged to two maternal lineages. The other lineage, referred as the southern lineage, was inferred to represent the Iberian subspecies of the blue tit. Altogether, 13 nucleotide substitutions separated the northern central haplotype and the most distant southern haplotype (IV).