The sunbirds or spiderhunters are small passerines from the Old World. Their range extends from Africa to Australia, with over 130 species in 15 genera.
In Tanzania, Moreau’s Sunbird (Nectarinia moreaui) and Eastern Double-collared Sunbird (N. fuelleborni) meet along an approximately 6 km wide hybrid zone. Species boundaries are preserved by ecological competition and divergent songs. The differences in songs are probably maintained by within-species social selection on song learning predispositions (McEntee et al., 2016).
McEntee, J. P., Penalba, J. V., Werema, C., Mulungu, E., Mbilinyi, M., Moyer, D., Hansen, L., Fjeldsa, J. & Bowie, R. C. (2016). Social selection parapatry in Afrotropical sunbirds. Evolution 70, 1307-21.